Thread: Heat Pump temperature drop

What is the acceptable temp drop for residential heat pumps in cooling cycle? I believe A/C units are expected to be in the 14-20F range.

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Originally Posted by Brent Crouse

What is the acceptable temp drop for residential heat pumps in cooling cycle? I believe A/C units are expected to be in the 14-20F range.

Heat Pumps in the cooling mode work the same way a standard AC system works.

Thanks Billy,

I might not be using the correct terminology. I've always called the difference between the return air and the cooled air, "temperature drop". I've been told that 11F is acceptable for heat pumps, whereas it would not be for a standard A/C unit.

Originally Posted by Brent Crouse

Thanks Billy,

I might not be using the correct terminology. I've always called the difference between the return air and the cooled air, "temperature drop". I've been told that 11F is acceptable for heat pumps, whereas it would not be for a standard A/C unit.

Could be for for that System.

Never seen a temperature differential on a A/C unit nor a heat pump, maybe different terminology.

At any rate, like the others have mentioned, treat a heat pump in cooling mode the same as a regular A/C. Hard and fast rules don't really apply for either, temperature differentials are just one factor of evaluating a system. A properly functioning system might have as little as a 11 degree differential between the supply and return air temperature or as much as a 20 degree split. It depends on the unit and the installation. Higher efficiency units will have less differential than older less efficient ones as a general rule. Differentials will also vary according to the weather and indoor ambient conditions, including humidity load.

I've never seen a label anywhere which specifies a TD (temperature differential).

Too many things which could affect it.

The rule of thumb I've always heard is 15-22, however, my rule of thumb is ... that taking the TD is basically useless (because so many things affect it and can give false 'in the range' TD readings when nothing it right with the unit).

Most charging charts that I have seen refer to superheat (differential between the temperature of boiling of refrigerant and the actual temperature of the refrigerant at the suction line of the unit) not the temperature differential of the air in the ducts, but hey it has been quite a while since even trying to charge a system. Things may have changed a bunch since back in the dark ages when I did it for a living.
I would think pulling the panel and trying to verify the charge is way beyond the typical HI, I know I don't.

On all residential systems the temp drop should be between 18 and 21 degrees 17 or 22 is ok but could mean the fan speed or the system charge might be off. to check the system charge you need to check the super heat or the subcooling. air flow should not be restricted ie.. clean filter dirty evap coil

Originally Posted by Kevin O'Connell

On all residential systems the temp drop should be between 18 and 21 degrees 17 or 22 is ok but could mean the fan speed or the system charge might be off.

Where do you get that information from?

Inquiring minds would like to know.

If one is just taking temps at the supply and return vents I have found that new heat pumps do have less of a differential than an AC condenser will. Again there is way to much going on to rely on that. I take temps at those supply and return vents primarily to find if it is the same throughout the home. Whn I do this a heat pump is generally around 11 to 13 degree diff. An AC condenser system is anywhere from 15 to 20. This also depends on the age and seer rating of each unit. The fluctuation from home to home on decent working and maintained systems is in part from the seer of the units along with age and wear and tear of the units as well as outside temp, wind, humidity. Some homes it is 15 and the next home with a newer sytem might be up at 20. It really does mean nothing in the efficiency of any system. You simply cannot judge any real findings on taking temps at the return and supply other than...yup, it appears to be working and the temps are consistent around the home. Now if you find wide swings of 5 degrees and up then you know you have a problem with supply

Originally Posted by Jerry Peck

Where do you get that information from?

Inquiring minds would like to know.

I am a NATE certified in Gas heating, Air Conditioning & Air to air Heat Pump, I also work as a residential service technician.

Originally Posted by Kevin O'Connell

I am a NATE certified in Gas heating, Air Conditioning & Air to air Heat Pump, I also work as a residential service technician.

But ... where did you get that information from? That was the question.

The TD by itself is not telling you anything, and, unless you have reliable documentation which states otherwise, your numbers are WAY OFF, besides being meaningless numbers.

Originally Posted by Jerry Peck

The TD by itself is not telling you anything, and, unless you have reliable documentation which states otherwise, your numbers are WAY OFF, besides being meaningless numbers.

You're right Jerry.

Depending on what the latent (moisture) load is on the evaporator you could have a dry bulb temperature differential as low as 12º to 13º or as high as 21º to 23º.

If you want to take some readings of value don't take just dry bulb temperature readings include wet bulb readings with them.

With the wet bulb and dry bulb readings you can obtain a lot more valuable information.
If you have a half way accurate reading to determine how much air the fan is moving and an enthalpy chart you can plot how efficiently the equipment is operating breaking it down into total BTU's, Sensible BTU's, and Latent BTU's.

Measuring dry bulb temperatures alone only adds confusion to a situation where a piece of equipment might be operating properly.

Then you have the guys who try to measure temperature differential with a infrared thermometer.

I've been telling them to not bother taking the TD for years now, and those taking it with an IR thermometer - yes, you are right and I will add .

Taking TD with an IR thermometer is like taking the temperature of the water in your vehicle's engine by measuring the temperature of the exhaust pipe at the rear.

But, the HI schools keep cranking out HIs who *have been told that a TD between 15-22 means the system is operating properly*, and now I find out that something called NATE for HVAC techs is saying that a "temp drop should be between 18 and 21 degrees 17 or 22 is ok", and that is even worse than HI schools telling HIs the TD means anything - those guys (according to the site) are supposed to be the best HVAC guys.

Have you heard of NATE before (I had to look it up on the web)?

There may be one or two inspectors in the country that take wet and dry bulb readings but that may be exagerating. They are generalists and temps taken by home inspectors is either going to be a thermometer in a supply vent or IR readings throughout the home to get a general idea of operation.

No, readings at the supply and return mean about nothing but GENERAL operation and other areas of inspection added in with that will allow them to give a GENERAL idea of the systems condition and operation.

So in saying that the IR readings do not mean nothing but they actually do mean something. As in the general overall view added in with other areas of inspection of the system. That is like saying we should bring gages with us to test the charge of the system. There may be one or two inspectors that do that but I personally do not know any.

Oh well, this is all old info but I figured I would waste my time posting it.

Originally Posted by Jerry Peck

But ... where did you get that information from? That was the question.

The TD by itself is not telling you anything, and, unless you have reliable documentation which states otherwise, your numbers are WAY OFF, besides being meaningless numbers.

In Refrigeration and Air Conditioning Technology, 5E it states that based off of the return air temp to the suppy air temp should drop 20 degrees as it crosses over the evap coil. ie.. if you have a RA of 75 your SA should be 55 if you are at 50% relitive humidity. humidity will affect the reading, when we look for the 18 to 21 degrees of delta t (temp drop) that gives us a snap shot of how the system is operating. if it is out side of this range there could be some underlying issue that would involve further tests. But taking a Delta t reading is just a snap shot. and you should use a probe thermometer not IR just before the filter, unless it has a humidifer bypass (before the bypass) and about 18 inches from the evap coil if possiable.

Originally Posted by Kevin O'Connell

In Refrigeration and Air Conditioning Technology, 5E it states that based off of the return air temp to the suppy air temp should drop 20 degrees as it crosses over the evap coil. ie.. if you have a RA of 75 your SA should be 55 if you are at 50% relitive humidity. humidity will affect the reading,

That starts to get into better information, but ...

when we look for the 18 to 21 degrees of delta t (temp drop) that gives us a snap shot of how the system is operating.

No it does not. Not based on what you just stated.

You need to do dry bulb and wet bulb temperatures then chart it out, just as David said.

Originally Posted by Jerry Peck

That starts to get into better information, but ...



No it does not. Not based on what you just stated.

You need to do dry bulb and wet bulb temperatures then chart it out, just as David said.

Here is a site that has some good information when it comes to system checks to include temp drop and condenser split. you can read it online for free. I hope this helps with some questions that do arise and help with answers. according to this even I was off on my temps by a few degrees.
Study a Free HVAC Troubleshooting Manual

I'm with the masses, unless there is at least a 12 degree TD I would not look further, maybe a comment to refer to a technician to evaluate if it is questionable. There are WAY to many variables. I am also certified in a/c but a full evaluation is beyond the scope of a standard HI.

I've walked into an HVAC business before and actually sat down with a manager and said, "Listen, I have a question that is drivin' me and every other home inspector crazy."
"What is the range I should be looking for in A/C drop?"
ANSWER? 14-21 as a "general rule" I live in VA
BUT ...too low or too high you need to look for basic problems that could be causing it from, dirty filters, dirty coils, lack of refrigerant/ leak (Good luck with that one...even for pros to find), vents in home closed can even slow down air flow and create a greater temp drop near the coil as it is not moving as fast ... on and on.

Temp drop on a data tag? Wow,,that is a new one. I'll be looking this morning to see what I've been missing.
I know every furnace I've ever inspected has a "Temp Rise" right there on the data tag.

...This equipment in my opinion is the most complicated area of the inspection. A/C units.
One day I caught myself tryin to figure out why I was not getting more than a 10 degree drop on newer equipment. I'm thinkin' well anythings possible...thought and thought...then realized I've got the thermostat set at a point where it's being satisfied with the damn fan running.
It gave me exactly what I was asking for.
What an idiot.

I'd love to see a rquirement in real estate that states the seller must have had the HVAC system serviced in heat and ac in the last 12 months ...
OR require home inspectors to go to school for enough training to pass a test with some real teeth in it on HVAC systems.

You guys who are using, backing, and supporting the use of TD for assessing the condition or general condition of a/c systems really need to get your heads out of your butts. I hate to be that blunt, but nothing else it getting your attention.

I will repeat what I have stated here many times before:

Let's say you measure a TD of 18 degrees F, really pretty good, huh? So you write that down and go on about your merry way.

You get a call from your client a month later and you to pay for repairs to their system, which they had cleaned at your advice, and the HVAC guy found several things wrong that your client now expects you to pay for.

You respond "It was working fine what I inspected it, the TD was 18 degrees."

You client responds "Yes, the TD was 18 degrees, but the supply duct was mostly crushed, which you DID NOT report, and when my a/c guy fixed that the TD dropped to 10 degrees because now full air was flowing over the coil, so he went out and checked the unit, finding it low on refrigerant, and ... "

Keep checking TD because that is what the HI schools say to do, because it is quick and easy. Just be aware that your TD taking has no bearing on how the unit is working or its condition and will be of no use when you try to support your report's statement that it was 'functioning properly'.

Jerry, Jerry, Jerry

I do not think anyone above (I think not) is saying that doing a quick temp reading at supply and return vents is giving them the final definitive answer on whether or not the system is absolute perfect operating condition and I do not and have not ever seen in anyones report that does those quick temps where they stated because of that the system is absolutely perfectly, marvelous great undeniable perfect operating order.

You are getting way out of control with condeming everyone that does that. That is just part of what they do when scurrying around the home checking the overall homes fit and function. It is by no way the only thing they are looking at in an HVAC system inspection if any of them are at least following their state or association guidelines.

Does that temp reading tell them anything....Yes....Is it the final answer to alllllllllllllllll......................No.

I love you opinions and knowledge in multiple areas on this site and your overall knoledge of code.

Condeming people and telling them to get their heads out of their asses is way out of line.

No home inspector (maybe a couple) is going to bring gages with him or do a wet and dry bulb test on the HVAC system.

Almost no home inspector is going to tear open a sealed A coil cabinet.

All inspectors are going to look at the exterior of ducts and get a general opinion of their condition and the condition of what connections he can see. If he did n ot do a quick check on the supply vent to see if it is even blowing hot or cold air and the duct was disconnected somewhere he could not see....Then he would be paying for repairs. He is not going to pay for repairs because he took a temp reading at all supply and they were all within a few degreees and a reading at the one or two returns to get some kind of differential.

Please stop injecting you absolute opinion of what others may be doing to help to ascertain a general condition of a system.

If you want to help then make a *SUGGESTION* to them in maybe how to word their report that this differential does not warranty or guaranty that this system is in perfect running order by any means but just gives and overall view along with many other areas of inspection of the system combined together as a whole.

But to tell anyone that does this type temp reading for a general finding of function along with the rest of the inspection on the unit in the attic or where ever and the Condenser/heat pump outside and duct work, to get their heads out of their asses is out of hand and out of control and against the professionalism you normally exude.

Originally Posted by Jerry Peck

You guys who are using, backing, and supporting the use of TD for assessing the condition or general condition of a/c systems really need to get your heads out of your butts. I hate to be that blunt, but nothing else it getting your attention.

I will repeat what I have stated here many times before:

Let's say you measure a TD of 18 degrees F, really pretty good, huh? So you write that down and go on about your merry way.

You get a call from your client a month later and you to pay for repairs to their system, which they had cleaned at your advice, and the HVAC guy found several things wrong that your client now expects you to pay for.

You respond "It was working fine what I inspected it, the TD was 18 degrees."

You client responds "Yes, the TD was 18 degrees, but the supply duct was mostly crushed, which you DID NOT report, and when my a/c guy fixed that the TD dropped to 10 degrees because now full air was flowing over the coil, so he went out and checked the unit, finding it low on refrigerant, and ... "

Keep checking TD because that is what the HI schools say to do, because it is quick and easy. Just be aware that your TD taking has no bearing on how the unit is working or its condition and will be of no use when you try to support your report's statement that it was 'functioning properly'.

Well instead of telling us all that what we are doing is completely and totally wrong, how about telling us what we should be doing..

If you want to put this issue to bed once and for all lets establish a method here and now of EXACTLY the steps that should be taken by a competent HI to evaluate the A/C condenser/compressor function during a Home Inspection.

Originally Posted by Kyle Kubs

Well instead of telling us all that what we are doing is completely and totally wrong, how about telling us what we should be doing..

If you want to put this issue to bed once and for all lets establish a method here and now of EXACTLY the steps that should be taken by a competent HI to evaluate the A/C condenser/compressor function during a Home Inspection.

Fact is he cannot because if he did he would be putting you into the HVAC field and way beyond a home inspection.

That is what is wrong with the inspection part of being a home inspector.

An HVAC contractor is going to test each and every eletronic component (you won't) and HVAC tech is going to (maybe) do a wet and dry bulb reading (you won't) and HVAC tech is going to throw a gage on the system and check the refrigerant charge (you won't) An AC tech may (or may not) rip open the seal around the Evaporator coil cabinet and check the cleanliness and condition of the coil (you are not)

You are and can only be a generalist in the inspection department of an HVAC system. That is all you are there to do. Your general findings for the duct work and their connections, AC condenser, Air handle, maybe the Coil in some systems that you can get to without breaking a seal on the system, lower end of a combustion chamber, flues pipes, installation, condensation drain system, electric heating coils etc etc etc etc

Of course not all is mentioned what we check but again it is the general conditiuon, age and operation of the unit that you arew checking so there is absolutely nothing wrong with going from vent to vent taking a quick reading.

Originally Posted by Ted Menelly

I do not think anyone above (I think not) is saying that doing a quick temp reading at supply and return vents is giving them the final definitive answer on whether or not the system is absolute perfect operating condition and I do not and have not ever seen in anyones report that does those quick temps where they stated because of that the system is absolutely perfectly, marvelous great undeniable perfect operating order.

I have not said they are saying the systems are "absolutely perfectly, marvelous great undeniable perfect operating order", only that they are using them in determining that the systems are "functioning".

Go back and read their posts, then read mine.

There is no need to take a TD, it shows nothing or next to nothing (unless you do as DavidR says, and then it is part of the evaluation of the system).

How many home inspectors take dry bulb AND WET BULB temperatures? Close to zero probably.

How many of those then look and use the chart to see what that is showing? Even closer to zero probably.

Originally Posted by Jerry Peck

I have not said they are saying the systems are "absolutely perfectly, marvelous great undeniable perfect operating order", only that they are using them in determining that the systems are "functioning".

Go back and read their posts, then read mine.

There is no need to take a TD, it shows nothing or next to nothing (unless you do as DavidR says, and then it is part of the evaluation of the system).

How many home inspectors take dry bulb AND WET BULB temperatures? Close to zero probably.

How many of those then look and use the chart to see what that is showing? Even closer to zero probably.

Agreed. Taking a measurment of TD shows only that the system is operating. Does it show proper operation? NO WAY. As with many other apliances, the only way to assure proper operation is to refer to the manufacturers specifications.
Depending on return air temp, humidity levels, outside temp, and airflow, i've designed and seen system temp. drops anywhere from 5 or 6 degrees all the way up to 30 degrees. So, your temp drop of 10 degrees may show proper operation, or it may show the system is way off (I work as an engineer at a rather large HVAC manufacturer in Indianapolis, shouldn't be hard to figure out which).
Even if the HI takes entering and leaving dry bulb and wet bulb temps, that shows next to nothing. You would also need measurements of the airflow, to calculate the sensible and latent capacities. You would then need a measure of the total power used to calculate the efficiency.
But, remember, the efficiency calculated is just the efficiency at that operating condition. It is NOT the SEER rating of the unit. The SEER rating of a unit is based upon multiple tests at multiple indoor and outdoor temps and humidity levels.

The temperature drop across the evaporator is normally 18-20 degrees on a properly charged A/C with a clean condenser and clean evaporator and filter and the proper CFM of 400 cfm per ton. The home inspector can't and does not have the time and it is not even part of the home inspection to check, head pressure and suction pressure along with amp draw and coil temperature and super heat and sub cooling tempertaures. I can charge up an A/C with an R-22 tank, one hose and a thermometer and it will be correct. I thought this site was to help each other and not be so critical of one another. I don't care what anybody says, I saw an A/C the other day and the temp drop was 14 degrees and I recommended an HVAC professional to service and evaluate the system, it wasn't working correctly. When the coil temperature is to high because the system is under charged or dirty or it is running high head pressure because of a dirty condenser, you can't dehumidity nothing,and it can take 3-4 hours to cool the house down if it ever does and never shuts off. An oversized condenser is even worse, it will cool the house down too fast and won't run long enought to dehumidify so you have a cool sticky house. Also the duct work needs to be sized properly to handle the CFM of the blower. What good is a 3-ton condenser if you can't get 1200 CFM across the evaporator because the duct work is to small. I've been in the HVAC business for over 30 years. I'm keeping my thermometer.

Originally Posted by Dan Hagman

I'm keeping my thermometer.

And YOU are qualified to use it.

Most home inspectors, and some HVAC techs it seems, are not qualified to use a thermometer.

Now put that 2x4 and nail gun down and back away, slowly, slowly, ...

Originally Posted by Jerry Peck

There is no need to take a TD, it shows nothing or next to nothing

It shows nothing.
There has to be more information gathered for the dry bulb differential to mean anything.

If you have some method of determing how much air the fan is moving you can get a pretty good idea how much the sensible BTU delivery of the equipment is but not total BTU delivery.

If you're going to mess with drilling a hole for a temperature probe go ahead and drill it a little bigger so you can get a wet bulb reading too.
Testo makes one instrument that will do dry bulb and wet bulb for a little over 150 bucks.

You can get a close idea on fan airflow by measuring static pressure and plotting it on the equipments fan performance data.

With a little practice you can obtain all this information in as little as ten minutes and know more about the HVAC equipments operation than most HVAC guys will.

400 CFM per ton is a rule of thumb too.

[quote=Kyle Kubs;90308]Well instead of telling us all that what we are doing is completely and totally wrong, how about telling us what we should be doing..

If you want to put this issue to bed once and for all lets establish a method here and now of EXACTLY the steps that should be taken by a competent HI to evaluate the A/C condenser/compressor function during a Home Inspection.[/quote]

Aahem...

Stumbled across this new potential new way of checking refrigerant levels.

Of course, each unit being different, not sure how you'd know what values to consider acceptable, unless it's stamped on the unit's label.

Energy-saving Method Checks Refrigerant Level In Air Conditioners

To get an accurate engineering differential for an air conditioning system or a heat pump in cooling mode you need to acquire a wet bulb temperature and a dry bulb temperature at the return side and then a dry bulb temperature at the supply side of the system. You can then calculate a target differential using your engineering chart with a plus or minus 2 degree Fahrenheit error value. I am attaching the chart I use by Advanced Energy. It has never failed me yet. The only consideration is that the interior environment needs to be dry bulb of at least 70 degrees Fahrenheit. Wet bulb temperature is simply if you took your thermometer and wrapped a wet towel around it. I use what the mechanical contractors call a sling that calculates the wet bulb for you. Fluke makes a nice one and has a very fast temperature response time.

Hey Michael,

I can't read the chart. Too blury. Do you have a web link or clearer pic?

BTW, I used to go to NAHI meetings with you in Maryland. You used to work with Ed right? I was the young guy. My company then was Overbrook Home Inspection. Glad to see you're still inspecting.

Seriously

Wet and dry bulb tests, charge of the system, you might as well do a complete HVAC system tests that a good HVAC man would do.

If, and I say If, any of you are talking about a home inspection with all this tesing going on and half the time that you are normally at a home inspection is used up then I say good luck to you. While you are at it why don't you take measurements around the homem of the foundation and draw yourself a scaled drawing of the home and make all your notations of mesurements.

Hmm, what other parts of the home could we spend at least an hour alone on

OOOOOPS, I forgot, why don't you do pressure test on all the supply vents

Why don't the pros here just remember one thing. We are talking of home inspectors tests with out spending half the normal home inspection time to do so. If you are so hot to go out there and make all those tests and you are a home inspector then I suggest you give up home inspection and get out there and advertise for mor HVAC work.

Other than that your all getting way out of control.

DAVE R

No insult internded but get a grip. For you to say that taking a quickie test of temp at the supply vents does absolutely nothing.....Hmmm.... Seriously...forget you are an HVAC guy and then rethink that absurd answer and stop telling people it means nothing.

Generally speaking and if you did not hear it GENERALY SPEAKING, it does say a lot for that quick 2 second check. If you open your mind and eyes and pay attention that home inspectors are checking several other areas of the HVAC system and that quickie 2 second test speaks volumes.

Is the duct even freaking connected

IS there cold (or hot) air blowing out of it

If air is blowing out of it what, roughly, is its temp.

Are they somewhat all the same temp

Now go into the attic and after thaose quicky test see what may be going on as to, IS that duct hooked up, are there kinks in the duct. Are the rest of the connections pretty much air tight etc etc etc etc etc etc

Do I need more Etc

SO, AFTER ALL THAT COULD YOU PLEASE STOP SPINNING STORIES ABOUT THE QUICKIE TEST OF POINTING THEIR THERMOMETER MEANS NOTHING.

We are generalists and as generalists it helps us to make an overall opinion of the system along with multiple other tests and inspections we are doing. Checking the HVAC system out already consumes a good protion of our time. If we wanted to be HVAC techs (which by the way we find serious amounts wrong with brand freaking new systems that HVAC installers screw up all the time) we would get jobs as HVAC technicians.

Oh yeah....all those stupid little tests that home inspectors do find all that crap wrong with those systems.

Ted,

Your long and incorrect rant boils down to this equivalent:

Would you plug a circuit tester into a receptacle outlet, read the voltage, then proclaim that the electrical system and panel is in okay condition?

If not, why not?

It is telling you just as much about the "electrical system" and the "electrical panel" as taking a TD at the air handler supply and return is telling you about the "air conditioning system" and the "air handler/evaporator coil unit".

If one works, why not use the other? Using both will save tons of time and tell you just as much information as the other about its system.

Dang! I measured 123 volts! That is withing the VR ("voltage range" as opposed to TD) as I should find and THAT indicates the electrical system and the panels are all okie dokie.

Sound silly? You bet.

Just as silly as taking a TD and pronouncing that the air conditioning system is working properly.

Hey, wait a minute, if you measured 123 volts at a receptacle then that VR is actually telling you MORE than the TD told you.

Jerry

Now you are just being silly and again getting way out of control.

You are trying to pick the one quicky point and shoot of an IR thermometer as the entire eval of an HVAC system

I did not say that in the slightest. Not even remotely did I say that or intend it to mean anything that you are saying.

You are just attacking to make a mute point.

You have the AC on. You point the IR at a vent as you walk thru a room. What does it tell you. Oh my GOD. It says it is blowing 95 degree air and it should be blowing cold air. Or it is not blowing any air anddddddddd it should be because the system is on. etc etc etc

Come on now. Admit it. You can do it. That stupid quicky test does tell you something and coNtibutes to the rest of your inspection.

Shhh, don't say it. I know you can keep from saying it. Comeon. Thats it. Thats it, Yes.....I new you could admit it does tell you something. And no I am not using a three light tester to tell me the condition of the entire electric system by doing that stupid little test.

I am proud of you for admiting it Jerry. I just new I could count on you. You have kept my faith in you.

YOU ARE DUH MAN.

Originally Posted by Ted Menelly

Jerry

Now you are just being silly and again getting way out of control.

You are trying to pick the one quicky point and shoot of an IR thermometer as the entire eval of an HVAC system

I did not say that in the slightest. Not even remotely did I say that or intend it to mean anything that you are saying.

You are just attacking to make a mute point.

Nope, incorrect.

The discussion is about taking TD and then using that to determine that the a/c system is functioning okay and the TD tells you nothing more about the functioning ability of the a/c system that taking a VR (voltage range measurement) at a receptacle tells you about the functioning ability of the electrical system.

YOU may be trying to turn this into a IR measurement of the TD versus a air temperature sensing thermometer measurement of the TD, but THE DISCUSSION is about taking a TD and its meaningfulness or meaninglessness, without regard as what was used to measure the TD.

Keep on track, Ted, and don't try to take this from a discussion about the lack of usefulness for TD measurements.

Regarding your last part of your rant, you could hold you hand up and feel cold air coming out of the supply, which simply shows it is blowing cool air, not that is is working as it should be. Using an IR thermometer for that instead of your hand only tells you the same thing. By the way, NEITHER of those actions is taking a TD, which is what the discussion is about.

I guess 98 % of the inspectors out there are going to have to disclaim the HVAC. I want to know how Jerry test the A/C during his Inspections. Be truthful I know your a lefty and stretch the truth to your liking

Jerry

If nothing else you are making my point completely about TD.

If you read all your posts there is about nothing a TD will tell anyone due to the fact that so much more depends on that finding and charts and charge and proper sized this and that and air temp readings at vent and and and and

We are generalists. We are not going to test a system and follow charts anywhere near what an HVAC man is going to if he is completely evaluating a system. Open the unit up (only to a point with out destroying any seal that may have been made at the unit). Do a couple of quick checks. CHeck the gas connection, electric connection, is it blowing cold air, check the electric heating coils (if its electric), check the flue connection and the flue pipe, general cleanliness amp draw for the AC condenser, breaker sizes and I am not getting into all the rest. It is GENERAL OPERATION AND FUNTION OF THE SYSTEM.

Don't do this cause it will tell you nothing, don't point an IR therm at the vents. Don't hold your hand in front of the vent cause that only tells you if the blower is working.

Get the charts out. Size the system for the home, check the charge, wet bulb and dry bulb test, air volume test and oh yeah lick it and see if it tastes like chocolate

We are not AC men. We are generalists. Any little quick check anywhere in the system is going to give us an overall view.

Oh yeah, that little vent temp check gives almost the same temp readings as if you do it at the evaporator coil The numbers are almost identical to all the numbers everyone keeps touting. That 3 hour on the air handler/gas fired forced hot air/AC condenser testing etc etc etc Aint ever going to happen. You made my point with every single post you posted on here. So to tell folks to get their heads out of there butt does about as much as the discussion about all the other test and procedures and charts and air flow etc etc etc

Like I said Jerry. I was not ranting in the slightest. You and evryone else was when it comes down to a general home inspection.

All that testing and charts and measuring a homes cubic feet, window and door opeing measuring, humidity checking, wind blowing, wet bulb, dry bulb, lick it to see if it tastes like chocolate aint ever going to happen in a home inspection. And yes you brought up the home inspection schools and their suggestions for test to be done and how to do them.

Sooooooooo, "rant" away and have a happy day. Cause when you do you are making my point completely

Oh yeah, "keeping on track" ????? That is where I was trying to get you folks back to. Doing an HVAC system check as a home inspector. Not an HVAC company.

TD test, Yes, that was the discussion but pertaining to a home inspection as that is what it was all about. Does it tell anyone anything, yes it does, but just as a general operation of the system. Nothing definitive but something. Sooo, you TD testers out there, have at it, you are doing a great job as part of your *GENERAL* testing of the HVAC system.

THE ORIGINAL POST

"What is the acceptable temp drop for residential heat pumps in cooling cycle? I believe A/C units are expected to be in the 14-20F range."

YOU WILL GET THAT SAME READING POINTING MY FOOLISH LITTLE IR THERMOMETER AT SUPPLY VENTS AND RETURNS.

If you get a five degree 9throughout) differential at the supply and return then you will also get a small differential at the coil. Hence, sumpin wong wid dat system. "In general" Time to dig a little deeper or just turn it over to referring an HVAC company.

Oh yeah

Done with ranting now.

Originally Posted by Ted Menelly

DAVE R

No insult internded but get a grip. For you to say that taking a quickie test of temp at the supply vents does absolutely nothing.....Hmmm.... Seriously...forget you are an HVAC guy and then rethink that absurd answer and stop telling people it means nothing.

Generally speaking and if you did not hear it GENERALY SPEAKING, it does say a lot for that quick 2 second check. If you open your mind and eyes and pay attention that home inspectors are checking several other areas of the HVAC system and that quickie 2 second test speaks volumes.

Is the duct even freaking connected

IS there cold (or hot) air blowing out of it

If air is blowing out of it what, roughly, is its temp.

Are they somewhat all the same temp

Now go into the attic and after thaose quicky test see what may be going on as to, IS that duct hooked up, are there kinks in the duct. Are the rest of the connections pretty much air tight etc etc etc etc etc etc

Do I need more Etc

SO, AFTER ALL THAT COULD YOU PLEASE STOP SPINNING STORIES ABOUT THE QUICKIE TEST OF POINTING THEIR THERMOMETER MEANS NOTHING.

We are generalists and as generalists it helps us to make an overall opinion of the system along with multiple other tests and inspections we are doing. Checking the HVAC system out already consumes a good protion of our time. If we wanted to be HVAC techs (which by the way we find serious amounts wrong with brand freaking new systems that HVAC installers screw up all the time) we would get jobs as HVAC technicians.

Oh yeah....all those stupid little tests that home inspectors do find all that crap wrong with those systems.

No insult taken Ted on my part so don't take this the wrong way.

Your post shows a complete misunderstanding of basic HVAC fundamentals and assume way too much.

As a HI you say you are taking "general" measurements, when it comes to the HVAC system you are taking a measurement that only takes into account a quarter of the information required to make a half way accurate diagnosis and judging a systems operation off of that.
HVAC is not a "general" thing.

If you don't want to be an HVAC guy then quit taking measurements that involve it.
If you are going to take the measurements at least take the time to take a couple more measurements than you are taking now so you have enough information to make an accurate call as to what is going on.

With a temperature drop you know nothing, this part doesn't seem to be sinking in for some reason with some of you guys.

I've outlined how TWO additional readings that would take less than 10 minutes to obtain can give you the information you need.
I'm sorry if those readings might be too difficult for you to take but they really will provide your cleints with a more complete idea of what's going on.

Two readings is all it takes Ted, two readings.
Think you could squeeze an additional 10 minutes out of a inspection to gather some real information?

HVAC is all about BTU's Ted, how many BTU's can you tell are coming from a system running a 20º delta T?

With those two extra measurements you would be able to tell me, without them you know nothing.

No spin just heat transfer basics.

Originally Posted by DavidR

No insult taken Ted on my part so don't take this the wrong way.

Your post shows a complete misunderstanding of basic HVAC fundamentals and assume way too much.

As a HI you say you are taking "general" measurements, when it comes to the HVAC system you are taking a measurement that only takes into account a quarter of the information required to make a half way accurate diagnosis and judging a systems operation off of that.
HVAC is not a "general" thing.

If you don't want to be an HVAC guy then quit taking measurements that involve it.
If you are going to take the measurements at least take the time to take a couple more measurements than you are taking now so you have enough information to make an accurate call as to what is going on.

With a temperature drop you know nothing, this part doesn't seem to be sinking in for some reason with some of you guys.

I've outlined how TWO additional readings that would take less than 10 minutes to obtain can give you the information you need.
I'm sorry if those readings might be too difficult for you to take but they really will provide your cleints with a more complete idea of what's going on.

Two readings is all it takes Ted, two readings.
Think you could squeeze an additional 10 minutes out of a inspection to gather some real information?

HVAC is all about BTU's Ted, how many BTU's can you tell are coming from a system running a 20º delta T?

With those two extra measurements you would be able to tell me, without them you know nothing.

No spin just heat transfer basics.

Very professional reply David

I do appreciate all you are saying. You have to understand that we do not tear things down or drill holes. It is not our clients home yet. We are not an HVAC company the selleror owner has hired.

Also pleas understand that an extra 10 minutes here and an extra ten minutes there we might as well just keep on going. WE can only go so far in a General Home Inspection. Apply that ten minutes more for everthing we check in a home inspection and you will get an idea that it would amount to an overwhelming amount of time.

I do not do TDs, ever. If I did I would incorporate what you have said and more. Again, we have to stop somewhere. The understanding I was trying to convey has everything aboive I just wrote.

My quicky little temp taking will tell me a plethera of things to look for once I get to the system including duct work. If you want to call a TD taking temps at return and supply vents, then there you go. If those things are beyond limits then I just write what I find and referr or defer it off to David R because I have way to much more to do along with an hour or 2 of report on site or at home.

No we are not cheating or short changing anyone . We are not going to spend hours more in a home as generalists. This keeps folks from hiring someone from every single trade. When we find concerns with a water heater, dishwasher, broken rafters, no insulation roofing all screwed up, flashing gone wrong, chimnies needing work, broken dampers, screwed up slabs (I think you see where I am going with this) we defer it off to the appropriate tradesman. Then they only pay to bring those in that are required.

Thanks for the reply and not saying all home inspectors should take their head out of their arses.

Originally Posted by Ted Menelly

Thanks for the reply and not saying all home inspectors should take their head out of their arses.

Wouldn't even think of going there.

Since you like being general why not just say "HVAC present and accounted for"?

It doesn't get much more general than that.

Originally Posted by Ted Menelly

My quicky little temp taking will tell me a plethera of things to look for once I get to the system including duct work. If you want to call a TD taking temps at return and supply vents, then there you go. If those things are beyond limits ...

Ted,

It appears you still have not grasped what DavidR is saying.

... then I just write what I find and referr or defer it off to David R because I have way to much more to do along with an hour or 2 of report on site or at home.

Why write up something based on measurements which are meaningless?

That is part of what you are still missing in what DavidR is saying.

It is quite possible that "If those are beyond limits" that there is nothing wrong.

It is also quite possible that "If those are" within limits that there IS SOMETHING wrong.

Thus writing up based on "If those are beyond limits" is meaningless.

I'm not an HVAC tech, but I do get it and understand what would be needed, and I did not do that (what would have been needed to make TD reading mean anything) ... so I quite taking TD measurements many years before I retired.

Go ahead and take a reading on the supply in each room if you want, that is what I did, as that actually told me something: it told me how evenly the system was cooling. IT DID NOT, however, tell my WHY the system was not cooling evenly throughout the house if it was not.

That might not be a problem with the system as such, it might be heat gain from the exterior walls or large glazing areas, or insufficient insulation in those walls, or ... I just had no way of knowing, so I would report the inconsistent cooling throughout the house and let the HVAC techs figure out why. It might have been a duct work problem.

Take the house we had in South Florida as an example, the front bedroom was always the warmest in summer and coolest in winter, why? First, it had THREE EXTERIOR WALLS and no other room in the house did. Was there a problem with the a/c system? No. Was there a problem with the DESIGN of the a/c system? Yes. Did it need more CFM to that room? Probably. But that was up to the HVAC techs to address, not me.

Originally Posted by DavidR

Wouldn't even think of going there.

Since you like being general why not just say "HVAC present and accounted for"?

It doesn't get much more general than that.

It is not a matter of liking being general. You missed the point again. It is a matter of having to be general because that is what we get paid to do. Give the client a general overview of the home they are thinking of buying WITHOUT professing of knowing everthing about everything. Our liability is to great to get to deap into one item and then not as deep into all items.

Yes we have limits and for that very good reason. SOPs are there so we have to go so far and then they are there so we do not have to spend three days in a home and write a small book on the home inspection

I am not saying we keep it to that minimum. We just cannot and will not make professionals like yourself happy that we stripped a complete system (every system) That was not a dig, just a fact. If I were to walk into an inspection and profess to be the know all end all on every sytem and every single product in every home I would be committing professional suicide.

We simply do what we are paid for. As a matter of fact we are not even there to dictate to the client that this particular size system is even sized to the home. If we were to do that then we would need design software. We can give them a general size of system to approximate size of the home and thats it.

Sorry to disappoint you at the limits of home inspection but they are there for a reason and a good one at that. Even the SMoke detectors are mentioned generally. We could not get into the intricacies of a smoke detector system for many reasons. We test them with the button and not some phony can of smoke. We state that they should be in every sleeping room and outside those sleeping areas and that is about it. Other than wied together with battery back up. We give them info to follow up on either printed out for them of online.

Gees. By the end of all this and all the others threads and posts on this site you will understand what a home inspection is and is not. That was also not a dig.

Originally Posted by Ted Menelly

Gees. By the end of all this and all the others threads and posts on this site you will understand what a home inspection is and is not. That was also not a dig.

Sure doesn't sound like it should involve HVAC in any form, too general for that.

Jerry

I just read your last post. It seems we are doing the back and forth thing.

THE QUICK READINGS ARE NOT THE ONLY THING WE DO TO CHECK OUT AN HVAC SYSTEM

Everything you said about the three outside wall room I can almost say I can garranty you that i understand that better than you and would relay that to the client.

That is all part of a home inspection

I am not trying to be an ass here but seriously, you did home inspections. You know the countless items that go into a home inspection so it is not necessary for you to name all the reasons something may not be operating efficiently.

IT IS ALL PART OF A HOME INSPECTION. GIVING THEM A WELL ROUNDED NOTION AND OPINION THROUGH LOOKING, JUDGING, GAGING, FEELING SENCING, SMELLING, SIZING AND LICKING TO SEE IF IT TASTES LIKE CHOCOLATE.

When I clearly stated that that is not the only thing we do as a home inspectors in sizing up an HVAC or any other system.

Please stop with the temps at vents or TDs being the know all tell all. You are fully aware of the vast amount of items that go into a home inspection

There is no reason to go into every scenario of what goes into a home inspection or then David will know it all and we will have to shoot him

Originally Posted by Ted Menelly

I am not trying to be an ass here but seriously, you did home inspections. You know the countless items that go into a home inspection so it is not necessary for you to name all the reasons something may not be operating efficiently.
...
Please stop with the temps at vents or TDs being the know all tell all. You are fully aware of the vast amount of items that go into a home inspection

Ted,

You keep going back to "being the know all tell all" and I keep going back to "TD tell you nothing"

There is a BIG difference between those two ideas. *I* am acknowledging that TD "mean nothing", thus I keep saying "why bother doing them".

You keep going back to (not in this post, but in your other posts) that if the TD are outside your rule of thumb limits that it means something ... when TD mean NOTHING - not when taken as HIs take TD readings.

Go back and read my posts, then read DavidR's posts. For a TD to mean ANYTHING you need to do more things than just taking TD. You have stated that you do not have time to do more than just take TD, so I offered, being as you are pressed for time, *WHY BOTHER TAKING TD AT ALL*? It means nothing anyway and you get to save that time.

The answer is: Take TDs properly with the other measurements and calculation necessary to make the TDs actually mean something, or ... don't bother taking them. Heck, it will even save you time and you are apparently very concerned with time.

You told DavidR:

Gees. By the end of all this and all the others threads and posts on this site you will understand what a home inspection is and is not.

I suspect DavidR already understands what HIs do and their general nature, and that he is trying to help you eliminate a wasted effort taking readings which YOU THINK have meaning and they do not, so DavidR is trying to help you with your GENERAL inspection by avoiding the pitfall of taking misleading and erroneous readings and then trying to make them mean anything - which they do not.

DavidR IS NOT trying to get you to do the other things which would give TD readings meaning, he is simply telling you what is needed to give the TD readings meaning, and you can now make an educated choice as to whether or not to continue taking TD readings (with the other measurements to make the TD worthwhile) or to discontinue taking TD readings as they are meaningless.

YOUR CHOICE.

DavidR is simply trying to help you make an EDUCATED CHOICE.

I made that choice many years ago, and my choice was to not bother taking TD readings as they are meaningless.

Originally Posted by Jerry Peck

I suspect DavidR already understands what HIs do and their general nature

Yep, I have to explain why the 13º delta T measured with an infrared thermometer is okay.

Ted and Jerry,

Give it a break. If I want to spend 2 minutes taking three temperatures and 1 minute looking up the data, that’s exactly what I am going to do. I was taught this method by a very successful mechanical contractor and with our limited time and skills to assess a cooling system I find it the most efficient and accurate providing parameters are met. And quite honestly, I don’t care what you do on your inspections with three walls or twenty walls. With the posting numbers that you both have I don’t think that you inspect at all. I think you spend all your time here posting. Quite honestly I’m in the field inspecting or with my family. Get a life and stop pushing your agenda. Make a point and end it. 90% of this long thread are you two ranting. I’m out of here to do something worthy rather that not learning from you two.

Darn man

You guys are seriously hard headed

I don't know about you folks but with a serious under exageration I write up tens of thousands a month on HVAC system repair and replacement.

I think I must be doing something right

Speaking of that why is it that the pro on a specific system is the one that always screems the loudest that no one other than them could possibley know what is right and what is wrong. Why is it when push comes to shove most of or should I say all, in one way or another (allowances, repairs, replacement etc) the systems I write up get at the minimum of what I write up fixed and or replaced. Why is it when I write that there are countless factors behind my write up and testing of a system you folks just keep looking at the pointing an IR gun at a vent as if I am saying that tells one everything definitively. I don't have the time to write everything that determines my findings of an HVAC system. Almost everything in the home and the total construction of a home go into my write up of an HVAC system. How many times does one haver to repeat himself.

Why is it Davud (this is direct) you do not seam to have a clue after all the time on here and other sites of what a home inspection is or is not. And Jerry believes you do and is jumping thru hoops to express it.

Seriously some folks need to take at least the basic home inspection test or study of SOPs again and find out what a home inspection is or is not and then why it is or is not.

This has become agrivating just trying to put forth exactly that with out getting a back insult as to knowledge or experience or your all screwed up and ou don't know what you are doing or you gotta get your head out of your arse or you need to leave HVAC out of your inspection.

If it were not guys like me and all the rest of the home inspectors on this site our clients would be paying out all these repairs and replacements themselves and all we home inspectors would be in court on every home we inspect.

For Gods sakes man. Get your heads out of the tunnel and see there is light all around you and not just at the end of the tunnel.

Do you really think that home inspectors have no freakin clue and we are a bunch of ignorant idiots that are out there screwing up everything we look at.

How freaking insulting could the 2 of you possibley be to a bunch of home inspectors (almost 10,000) on this site.

No David. We do not bring a full compliment of HVAC testing equipment and drill freaking holes in someone elses equipment or tear apart sealed cabinets and if you really think we should then you really need to go check yourself and if Jerry is to keep backing you then he needs to go check himself because it don't happen. And guess what we still get our freakling job done and serve our clients well.

Oh yeah. All those clients and HVAC companies do not have there heads up their prospective arses either. Most are intelligent folks. They check our concerns and make the appropriate repairs. DO you even realise how much money home inspectors send HVAC companies on a yearly basis.

Freaking millions and millions yearly and not because we are all screwed up and do everything wrong.

Now....How is that for a damnrant???????????????

Pompous so an so's. Hmmm, and pompous about what. Geeeeeeeeeeeeeeeeeeees

Originally Posted by Michael Koser

Get a life and stop pushing your agenda.

You mean stop pushing like you are trying to push yours in your post?

My "agenda" is to help inspectors understand how things are, and if you do not want to understand that taking a TD is meaningless, so be it.

That does not stop those of us who know from trying to help the rest.

As for Ted, well he goes on and on and on about his way.

Kinda like you just did about your way.

If you want to be out inspecting or be with your family, fine, it you want to stop by here to learn, even better. If you learn faster than Ted, excellent, but don't knock how long it takes Ted to understand it just because you got it sooner (presuming you got it already).

I learned allot from this post and like the link to the e-book so it was well worth the eye burning read of the comments. I bet 9000 other I-News people did also. Keep up the good work David, Jerry and Ted...........

Originally Posted by Brent Crouse

What is the acceptable temp drop for residential heat pumps in cooling cycle? I believe A/C units are expected to be in the 14-20F range.

Unfortunately, this thread has gotten WAAYY out of control. Ted, Jerry, and David, you all seem to be arguing different points, and have valid opinions.

The original question refered to an acceptable temp drop for a heat pump. People have replied with their opinion of acceptable temp ranges. The true answer is that there is NOT an acceptable temp drop range. A measured TD, be it 5 or 25 degrees, is NOT a valid indication of correct operation. I think that is all Jerry is trying to say. As a guy who has a hand in the designs of the units being installed, I would agree.

Ted, I understand your responsibility as a home inspector. Indicate the system is blowing cold or hot air, and all installation methods of the unit and ductwork are correct or incorrect as far as you can tell. That is the extent of your responsibility to the inspection. State that and be done
with the HVAC part of the inspection.

To use a temp drop alone as an indicator that the HVAC system is, or is not operating correctly is incorrect. And, to add comment to your inspection report stating the HVAC system is faulty and should be repaired, based on a TD measurement is reckless and doing a disservice to your customer,IMHO.

Originally Posted by Ted Menelly

Why is it Davud (this is direct) you do not seam to have a clue after all the time on here and other sites of what a home inspection is or is not. And Jerry believes you do and is jumping thru hoops to express it.

Seriously some folks need to take at least the basic home inspection test or study of SOPs again and find out what a home inspection is or is not and then why it is or is not.

Lol.........I fully understand the concept of a home inspection Ted, it's the HVAC portion of it I have an issue with.
If it's going to be half-assed it doesn't need to be done at all.
Your clients take what you say as the gospel and when you provide them a definite determination with a quarter of the information required you didn't do your job.

You don't have a clue what is going on with just a dry bulb temperature differential, nobody depending on that single measurement does.
I will ask this again: How effectively is a system operating with a 20º temperature drop operating? How many BTU's is it removing?
If you're measuring this delta T without drilling holes near the equipment and doing it at the registers you're measuring in the wrong place anyway to determine equipment operation due to duct losses and gains.

I can't seem to understand why you are so close minded to grasping the basic concepts about HVAC myself and Jerry are trying to help you with.
Instead you attempt to turn this into a pissing contest by stating I'm pompous?

I can help you to learn this if you really want to, if anyone else is interested PM me and I'll be glad to help.

DavidR
Could/would you put together a procedure for testing, and post it here?
It should include how to interpret the results.
Thank you

Originally Posted by Rick Cantrell

DavidR
Could/would you put together a procedure for testing, and post it here?
It should include how to interpret the results.
Thank you

I would be glad to for those interested.

You'll have to drill holes in the equipment though Rick if there aren't any there.

I thought as much.
I think it would be helpful when someone ask the question
"Why didn't you....."
Well Mr/ Mrs client, the only meaningful method of testing involves..."

But at least we know how/what to do.

DavidR,
Danger Will Robinson, Danger.....
Complete testing procedures are going to be way above the scope of the HI and most inspectors.
I am curious, however, to read the procedure to which you are refering and are going to recommend to readers.
From reading your posts, you sound like you know a thing or two about AC/HP units, so I'm going to assume (yeah, yeah I know, I know) you understand that even dry bulb-wet bulb readings aren't nearly enough for a true evaluation of the system condition.
Checking the charge of the unit is also going to be necessary. That is something that most inspectors should NOT be doing. How many inspectors are licensed to handle refrigerants? And even more importantly, how many know how to do it without contaminating the system, or hurting themselves?
Don't forget, you'll also need the specifications for the unit from the manufacturer. The charging chart on the unit will get you close, but to truly know your operating correctly involves knowing the expected pressures and amp draws at different atmospheric conditions. Are you going to teach them the proper way to you an electric meter so that they don't electrocute themselves?
Although it would be good for inspectors to know proper checkout procedures for an AC-HP system, those procedures should be performed by a qualified HVAC technician.

Very Interesting thread. I have yet to see any of you guys say in detail "how a HI is suppose to check a system".

1. Turn the unit on.
2. Feel for air flow at the registers.
3. Cool and hot air.
4. Visual of the cabinet and feel for air leaks.
5. Visual of condenser
6. Visual of ducts.
7. Visual of flues.

Is this what we suppose to be doing? Add to the list as needed.

Originally Posted by Mike Schulz

Very Interesting thread. I have yet to see any of you guys say in detail "how a HI is suppose to check a system".

Waiting for the TD issue and discussion to be completed before going on.

1. Turn the unit on.
2. Feel for air flow at the registers.
3. Cool and hot air.
4. Visual of the cabinet and feel for air leaks.
5. Visual of condenser
6. Visual of ducts.
7. Visual of flues.

Is this what we suppose to be doing? Add to the list as needed.

Good start.

Originally Posted by Jerry Shipman

DavidR,
Danger Will Robinson, Danger.....
Complete testing procedures are going to be way above the scope of the HI and most inspectors.
I am curious, however, to read the procedure to which you are refering and are going to recommend to readers.
From reading your posts, you sound like you know a thing or two about AC/HP units, so I'm going to assume (yeah, yeah I know, I know) you understand that even dry bulb-wet bulb readings aren't nearly enough for a true evaluation of the system condition.
Checking the charge of the unit is also going to be necessary. That is something that most inspectors should NOT be doing. How many inspectors are licensed to handle refrigerants? And even more importantly, how many know how to do it without contaminating the system, or hurting themselves?
Don't forget, you'll also need the specifications for the unit from the manufacturer. The charging chart on the unit will get you close, but to truly know your operating correctly involves knowing the expected pressures and amp draws at different atmospheric conditions. Are you going to teach them the proper way to you an electric meter so that they don't electrocute themselves?
Although it would be good for inspectors to know proper checkout procedures for an AC-HP system, those procedures should be performed by a qualified HVAC technician.

What I'm referring to will give anyone doing the testing a very rough idea of what is going on with the system. It's about getting field BTU measurements. No need for gauges or compressor performance curves.

Yes the procedures can be picked apart as I've picked them apart myself.
I'm going to keep this very generic so that I don't go overboard into something like density correction factors, duct loss/gain, radiant cooling, and coil bypass issues.

There are three readings you need to obtain to roughly plot the equipments efficiency.
You need a wet bulb differential at the equipment, the dry bulb differential at the equipment and an approximate number of the air volume being moved by the fan in CFM.

The wet bulb numbers will need to be converted over to enthalpy values by use of a psychrometric chart or enthalpy chart like the one posted previously.
The dry bulb differential is what it is and the CFM can be approximated from static pressure readings and equipment fan data.

These numbers are then plugged into two formulas to calculate total and sensible BTU's

4.5 X CFM X enthalpy differential = total BTU's
1.08 X CFM X dry bulb temperature differential = sensible BTU's

You can subtract the sensible from the total to get a fairly close number of the latent capacity (moisture removal) of the equipment.

Before I start giving examples does this all make sense so far?
If it does you guys are smoking me when I first learned this stuff.

Heck DavidR
If I had known that was all there was to it,
I would have been doing it a long time ago.

Originally Posted by Rick Cantrell

Heck DavidR
If I had known that was all there was to it,
I would have been doing it a long time ago.

Pretty simple isn't it?

Waiting for next lesson.

I'll start posting examples after some of the other posters have had a chance to chime in.

I'm an HVAC guy, I have to keep things simple.