Thread: Ram air for HVAC?

I saw this air scoop on a return junction in an attic. Never seen one before. Any thoughts?

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Pesticide and insulation sucker-inner.

Possibly someone's unintelligent approach to adding "fresh air" into the indoor environment for "make up air"?

Someone that wants 800 a month in heating and cooling cost and like Jerry said, bugs and insulation.

Just what I thought too.....make up air. But why in the world would you take attic (unconditioned air) and put it into your conditioned air supply? This is a Centex home (I'm pretty sure) and they've done quality construction in this neighborhood. I've done three or four inspections in the same area (retirement community) and this is the first I've seen like this. I'm guessing this is an "ad hoc" improvement by an HVAC tech on a service call. I wrote it up as needing correction!

I install those all the time when the return air grill is to small for the system. This way you lower the static pressure and all is good.
I've seen plenty of air filters that are never changed and get suck into the return air, this would also fix that problem too.

NOT

Would be nice if you could get a pic of the evaporator and how pluged up it is, since it's been sucking unfilter air. I did a job that had a return air grill near the floor, and missing filter. The evaportar had like a 3/8" thick mat of dog hair/lint, and an expired pizza coupon stuck on it. Yuck!!

If I recall correctly there were three returns in the two bedroom duplex. The master and livingroom were 18 x 18s (or 20 x 20) and the smaller bedroom was a 14 x 14 (or 16 x 16). They seemed plenty big. As an HI I'm not required to to the numbers for the returns.

Originally Posted by Craig Ervin

I install those all the time when the return air grill is to small for the system. This way you lower the static pressure and all is good.
I've seen plenty of air filters that are never changed and get suck into the return air, this would also fix that problem too.

NOT

Would be nice if you could get a pic of the evaporator and how pluged up it is, since it's been sucking unfilter air. I did a job that had a return air grill near the floor, and missing filter. The evaportar had like a 3/8" thick mat of dog hair/lint, and an expired pizza coupon stuck on it. Yuck!!

Just a little curious why you would not install another small return or increase the size of one of the returns instead of sucking non conditioned air from an attic.

Originally Posted by Craig Ervin

NOT
!

Originally Posted by Ted Menelly

Just a little curious why you would not install another small return or increase the size of one of the returns instead of sucking non conditioned air from an attic.

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Are We reading Ted?
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*attachment example of sarcastic remark
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Originally Posted by Billy Stephens

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Are We reading Ted?
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*attachment example of sarcastic remark
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Ah////yep....Just seeing if you were paying attention.

Keeping you on your toes

Originally Posted by Ted Menelly

Keeping you on your toes

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Thanks,
.

Considering its installed on insulated ductwork are you sure its the return side? Nobody insulates the return side up here, even in unconditioned spaces. I'm thinking supply side to keep pipes from freezing.

Originally Posted by Markus Keller

Considering its installed on insulated ductwork are you sure its the return side? Nobody insulates the return side up here, even in unconditioned spaces. I'm thinking supply side to keep pipes from freezing.

.................................................. .................................................. ..

Well let's think about that one! If returns are NOT insulated you will lose energy from conditioned return air on its way back to the air handler. All the plumbing is buried beneath 12 to 15 inches of blown fiberglass insulation. I don't ever recall seeing a "flexible" return duct that was NOT insulated. I'm not sure it would pass code compliance in any AHJ.

If what you are saying is true (and I don't doubt you) I would expect it applies to solid duct work not flex. In our area, solid duct work in unconditioned space is insulated on the inside.

I would be interested in see pics of what you are describing.

BTW, both supplies and returns were insulated flex!

I agree you aren't really going to see uninsulated flex duct, unless the installer is goofy. Flex duct for main runs is considered crap work around here. Solid rectangular duct is the norm. Flex is mostly for runouts, length is restricted by occupancy and construction classification. The gray flex is mostly banned. (supposedly due to fumes during fires). Foil flex is primary.
I agree with you on the return side efficiency loss. Return side issues around here are a whole nother thread.

In our area I see quite a bit of large 18-20 inch supply coming from the air handler to elevated junction boxes suspended in the truss system. From there they drop individual supplies (flex) to each room. I call them spiders because thet's what they remind me of. These types of installations are fairly common in the tract houses. Custom installations are usually higher quality solid duct centerline with flex pulls to the rooms.

Originally Posted by Barry Lewis

Custom installations are usually higher quality solid duct centerline with flex pulls to the rooms.

Huh?

Haven't seen rigid duct in a home in years, regardless of how "high end custom" it was. Maybe I was looking at low end high end custom homes?

Originally Posted by Jerry Peck

Huh?

Haven't seen rigid duct in a home in years, regardless of how "high end custom" it was. Maybe I was looking at low end high end custom homes?

Here you go Jerry. Built in '04, 3800 Sq Ft 5 BR 3 1/2 Bath

Sale price $299,900

Originally Posted by Barry Lewis

Here you go Jerry. Built in '04, 3800 Sq Ft 5 BR 3 1/2 Bath

Sale price $299,900

And that is supposed to be "better" ... when that is not even done correctly?

Nonetheless ... *I* have not seen rigid duct in a new house, regardless of price, in a very long time.

I have now seen *your* photo of one done incorrectly.

Jerry,

Please be more specific as to how it is incorrect!

Originally Posted by Barry Lewis

Jerry,

Please be more specific as to how it is incorrect!

Barry,

The flexible duct is required to come off the metal attachment collar straight, be supported within 18" of the collar, then make its bends, being supported at the bend, then being supported at maximum intervals of 5 feet with maximum sag between supports of 1/2" per foot between support (5 feet maximum between support means 2-1/2" maximum sag, but not at 2 feet between support, that only allows for 1" sag).

I see what appears to be ONE strap in the photo ... ONLY ONE ... there should be at least TEN supports in that photo.

Jerry,

The two on the left go upward to a tray ceiling in the master bedroom. The far one on the right (with the hanger strap) goes to the master bath. The closer one on the right dumps into the master closet. The closer one on the left dumps into the area above the foyer adjacent to the master bedroom on the second floor.

The city approved the mechanicals for the installation.

My question would be , do you write up every technical shortcoming? I'm already considered the "pickiest" inspector in our area with the longest inspections.

Originally Posted by Barry Lewis

The city approved the mechanicals for the installation.

And we know what that means ...

My question would be , do you write up every technical shortcoming? I'm already considered the "pickiest" inspector in our area with the longest inspections.

Being as most (virtually all) of my inspections the last 4 years or so of doing inspections were new construction, yes - all things which were "not right" and which I knew about. Even on the homes which were not new construction, because 'they should have been done correctly back then'.

Which is why my reports were so long, and why I was there so long on the inspection, and why my clients paid me what they did.

Some inspectors look at things from this view point: If they are not "wrong", they are "right".

Other inspectors look at things from this view point: If they are not "right" they are "wrong". That was the way I looked at things.

Other inspectors look at things from this view point: If they are not "wrong" and maybe not "right", then, ... well, ... if they are not "wrong" they must be "right". WRONG!

There is no gray in there, they are either done correctly or they are not.

On that fiberglass duct board, each section is required to be mechanically attached to the next, the outer covering lapped and stapled to the other duct, then taped. The reason it is very common to find one section dropped in relation to another section was that they were not butted together with a proper joint, not mechanically fastened properly, and not strapped properly.

Jerry,

Agreed, if it's not right it's wrong! My inspections are 5 hours or more. I am as thorough as I can possibly be. I use a standardized reporting form but include lots of notations. I continually try to enhance my knowledge base with CEUs that keep me certified in the 2 states I work. However, it's impossible, for me, to "know it all" since I never worked exclusively in the building trades.

As for the duct work, it is metal, interlocked, with fiberglass insulation wrap and tape. I've yet to see fiberglass shell duct work in our area.

Thanks for you insights.

Originally Posted by Barry Lewis

However, it's impossible, for me, to "know it all" since I never worked exclusively in the building trades.

Barry,

Not to worry, it is also impossible for any of us, even having worked in the building trades, to "know it all".

I certainly do not and I am still learning more every day.

Metal duct work? I haven't seen metal duct work except in commercial structures, and even then they use flex whenever they can.

Jerry,

You'll get a kick out of this one. The B-Vent was routed through an interior chase through the attic and roof. Darn vent was in the way of the lower duct supply....well we will take care of that!

Anyway this is typical duct work in our area, both lower and attic stuff. Maybe we're behind the times in the northern Virginia.

Barry,

On another issue in that photo, I hope that expansion tank is supported properly, not only is it hanging off horizontally, but it is hanging off CPVC ... not even copper ... !

Regarding the duct work routed around that vent, I've seen where they have taken the duct and cut half moon shapes into the sides instead of running full size around it, and, yes, of course it was all done incorrectly.

The problem with that metal duct is all the joints, both the longitudinal seams and all the joints between sections - they tend to leak - a lot.

Well I MUST SAY THAT THIS VENT IN THE RETURN IN THE ATTIC IS A TRAVISTY AND SHOULD BE PUNISHED. WHY? WOULD YOU WANT TO BRING IN 150 DEG. AIR INTO THE A/C AND INCREASE THE HUMIDITY IN THE HOUSE AND DECREASE THE COOLING CAPACITY??
This is directed to who installed this incorrectly.

Originally Posted by Chris Wilson

Well I MUST SAY THAT THIS VENT IN THE RETURN IN THE ATTIC IS A TRAVISTY AND SHOULD BE PUNISHED. WHY? WOULD YOU WANT TO BRING IN 150 DEG. AIR INTO THE A/C AND INCREASE THE HUMIDITY IN THE HOUSE AND DECREASE THE COOLING CAPACITY??

Chris,

Welcome to THE inspectors board.

Did you read the above posts? Just curious.

Yes!, just my opinion.

Back to the original picture at this thread start, what that vent is for is to help suck in that aroma from the decaying dead rat that has been up there in the attic now for about a week.

The vent helps pull in that musk type smell that justs drives the ladies into a state of passion.

Aren't we jealous we don't have one our air handler.

rick

Someone mentioned that it was to ballance the pressure in the system. Like I originally said, if they added a short piece of duct coming from where that thing is installed and attached it to a small return vent in the ceiling just below it *like it should have been done to ballance the pressure in the system* then it would be drawing conditioned air into it instead of Ricks dead rat, insulation, hot humid air, insects etc.

Hopefully the young couple will take my recommendation seriously and have it repaired. I told the wife (husband couldn't be there) that she would be wasting ALOT of electricity and gas with cooling and heating if they didn't fix it. I often check back to see what they've done after the close.

In Barry's last pic, shouldn't that bundle of wire be called out, due to derating?

From the original picture, it is possible the installer or home owner wanted to introduce outside air, to balance their "home" or have their house slightly pressurized. It is not an uncommon practice.

Think of it in reverse. Do you write up a bathroom fan that exhausts to the exterior, causing outside air to leak into the house and waste energy?

Or if there is a large kitchen exhaust hood, with no make up air provisions. Do you tell your client it is a defect and that they will have to open the window and let in outside air, in when operating the hood?

It does use energy, but if applied correctly and knowing that it can have a cost penalty of energy usage, it performs a function. I wouldn't call it a "defect", because it is not against any code or against any ASHRAE design standard. In fact it is "good design practice" to introduce outdoor air to balance a home that has numerous intermittent or even continuous exhaust systems. I would let my client know that this may be part of the system design and it can increase the cost of energy, if not a balanced system. I would also advise that they should question the owner about knowledge or history of this detail and if unknown, contact a licensed HVAC contractor for review.

Originally Posted by Tan Da

In Barry's last pic, shouldn't that bundle of wire be called out, due to derating?

Yes, it should be.

Originally Posted by Ken Amelin

From the original picture, it is possible the installer or home owner wanted to introduce outside air, to balance their "home" or have their house slightly pressurized. It is not an uncommon practice.

Ken,

Did you read through the posts above?

That is what has been discussed. There are ways to do that and ways NOT to do that, and the photo shows a way NOT to do that.

Originally Posted by Jerry Peck

Did you read through the posts above?

That is what has been discussed. There are ways to do that and ways NOT to do that, and the photo shows a way NOT to do that.

Jerry,

Yes, I read all the posts above. That photo IS an acceptable way to do it.

Originally Posted by Ken Amelin

Jerry,

Yes, I read all the posts above. That photo IS an acceptable way to do it.

Ken,

Just to clarify ...

You are referring to the photo at the original post, right?

If so, maybe some of the others here can re-explain why that is a "bad thing", because I am obviously not able to convey that to you.

The repeat of my post


"Someone mentioned that it was to ballance the pressure in the system. Like I originally said, if they added a short piece of duct coming from where that thing is installed and attached it to a small return vent in the ceiling just below it *like it should have been done to ballance the pressure in the system* then it would be drawing conditioned air into it instead of Ricks dead rat, insulation, hot humid air, insects etc."

Just not a good idea. I could care less if it is an acceptable way to do it.

Originally Posted by Ted Menelly

"Someone mentioned that it was to ballance the pressure in the system. Like I originally said, if they added a short piece of duct coming from where that thing is installed and attached it to a small return vent in the ceiling just below it *like it should have been done to ballance the pressure in the system* then it would be drawing conditioned air into it instead of Ricks dead rat, insulation, hot humid air, insects etc."

Ted,

I read that in your first post.

Unfortunately, your suggestion to duct the return to the ceiling within the living space would not pressurize the system, as I believe was the intent in this detail. You can only PRESSURIZE the system if you introduce outside air. See my first post for my thoughts on system pressurization.

Originally Posted by Ken Amelin

You can only PRESSURIZE the system if you introduce outside air.

Ken,

Okay, let's go with that theory.

I have a house, I open the windows, is the house now "pressurized"?

No.

The only way to "PRESSURIZE the system" and thus the house is to introduce PRESSURIZED AIR. Introducing UNpressurized outside air does absolutely nothing toward your goal of pressurizing the system and the house.

Put forth your next reason and we can work through them one-at-a-time, explaining why they not only will not work but are also detrimental to the occupants of the house.

Originally Posted by Jerry Peck

Ken,

Okay, let's go with that theory.

I have a house, I open the windows, is the house now "pressurized"?

No.

The only way to "PRESSURIZE the system" and thus the house is to introduce PRESSURIZED AIR. Introducing UNpressurized outside air does absolutely nothing toward your goal of pressurizing the system and the house.

Put forth your next reason and we can work through them one-at-a-time, explaining why they not only will not work but are also detrimental to the occupants of the house.

I always work with my clients in not pressurizing . Return duct or jumper ducts in every room makes for a much more ballanced home with greater even cooling and heating in everyroom. Pressurizing the rooms makes for poor air flow and uneven heating and cooling. If it is ballancing the system then the ballance should be done with the amount of supply and the amount of return. The sytem being much to small or much to large then the system has to be ballanced with return and supply. Of course much to small and the system is running far to often and the sytem much to big does not allow for it to run long enough to get rid of the moist air in the home. I don't get this whole pressurizing thing. If the home is to tight like in a foam panel home then you would have a small amount of outside air in just for exchange purposes and fresh air.

Maybe its just me but I always have to question and maybe I will learn something.

Originally Posted by Ted Menelly

I always work with my clients in not pressurizing . Return duct or jumper ducts in every room makes for a much more ballanced home with greater even cooling and heating in everyroom. Pressurizing the rooms makes for poor air flow and uneven heating and cooling.

Ted,

You are referring to pressurizing "each room" because you put more supply air in that is taken out.

Ken is referring to pressurizing the system by allowing air into the duct (I still have not figured out how you can pressurize something by putting a pig old hole in it, but I'm trying to understand it.

Now, put that scoop on the hood of a car and drive it 60 mph, yeah, that will pressurize whatever is being fed by that scoop. But taking a stationary duct, cutting a hole in it, and expect it to somehow pressurize that duct is, well ... simply beyond me.

FRESH air inlets to the return air plenum will have the effect of slight pressurization which may be desirable under certain conditions (radon) high humidity, etc. and has it's proper place per Dr. Joe of Building Science fame.
If that is original photo is of a return, then it will pressurize the system when the fan is running, BUT that is a STUPID way to try to achieve "fresh" air inlet or pressurization. Connect an insulated duct to real fresh air and maybe a motorized damper and controller and you might have something other than a attic air induction system.

Originally Posted by Jim Luttrall

FRESH air inlets to the return air plenum will have the effect of slight pressurization which may be desirable under certain conditions (radon) high humidity, etc. and has it's proper place per Dr. Joe of Building Science fame.
If that is original photo is of a return, then it will pressurize the system when the fan is running, BUT that is a STUPID way to try to achieve "fresh" air inlet or pressurization. Connect an insulated duct to real fresh air and maybe a motorized damper and controller and you might have something other than a attic air induction system.

Yes I have seen many a system set up on a duct and damper to the exterior on a control that only calls for it when necessary but not always necessary by any means.

Now that I have said that I was serious about teaching me. Is it when barometric pressure is at a certain level and then the damper opens. If it is then I can understand that. I see most of them operated by , I guess you call it, a humidistat and only opens when humid air is needed on very dry times.

Originally Posted by Jim Luttrall

FRESH air inlets to the return air plenum will have the effect of slight pressurization which may be desirable under certain conditions (radon) high humidity, etc. and has it's proper place per Dr. Joe of Building Science fame.

Jim,

Do you have a link to that?

I have read some of his stuff, and attended several of his classes, and have not read nor heard that doing as shown, and as you describe, will pressurize the system and the house.

That helps in bringing in fresh air in a highly sealed home, yes.

But if there are the proper returns in each room (as required by the Florida Building Codes), there will not be any pressurization of the rooms (other than a very slight amount allowed by code - but that is based on the return being not quite totally sized to meet the code intent of no pressure difference on each side of each room with a supply and a closed door.

Now, *IF*, if an intake fan is installed in that fresh air vent, yes, that could slightly pressurize the system, based on the size of the fan in the fresh air duct, the size of the fresh air duct, and the ratio of that fresh air to the return air ... however ... the photo shows an open vent with *no* fan, and no way to pressurize the system.

As I recall, Dr. Joe's stuff always included a powered intake fan in the fresh air duct - and that is not present here.

I will have to agree with Jim, but the only acceptable way to bring in fresh air is with an ERV or HRV. If this was a tight building then it would have to have say an ERV installed. a true system has a load calculation and is sized correctly, and only then can you have a balanced system, and more likely it will have dampers installed at the plunem so any fine tunning can be done.

It is late but I have the Building Science Builder's Guide and found a short discussion in the appendix on page 419-421.
"With respect to the infiltration of exterior pollutants such as soil gas, pesticides, radon and below grade moisture, limiting the negative air pressure which can occur, providing positive air pressurization of building enclosures (or portions of building enclosures) as well as providing sub-slab or crawl space depressurization are appropriate strategies for control."

Originally Posted by Jim Luttrall

It is late

Jim,

Yes, it must have been late ... ... as that does not state what you stated above. That gives 3 options, it does not state that one creates another, and then, "as well as", it is providing 3 options to help control what is trying to be controlled.

I will underline the 3 options being given: (underlining and bold is mine, the bold is highlighting that those "are" "separate" strategies)

"With respect to the infiltration of exterior pollutants such as soil gas, pesticides, radon and below grade moisture, limiting the negative air pressure which can occur, providing positive air pressurization of building enclosures (or portions of building enclosures) as well as providing sub-slab or crawl space depressurization are appropriate strategies for control."