Inside humidity - 42, outside humidity - 14

Donna Brown · 07-16-2018, 07:46 AM

How can this be?

I needed a new heat pump this Spring. Was told I needed a 4 ton unit to meet my 1350 sf home. It was put in and immediately started "clunking"....return air opening was too small...adding extra return Monday, today.

I moved to AZ because of arthritis and the low humidity. The old heat pump (3 ton) was fine...no problems with the humidity...it just didn't cool the air any longer after 25 years.

Manufacturer told me by increasing the return air supply, it would lower the humidity in the house.

Can anyone tell me where the humidity is coming from when the humidity level outside is 14?

Thanks,
donna

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**Roy Lewis** · 07-16-2018, 08:29 AM

I believe a 4 ton is a little to being for a home of that size.
The unit doesn't run long enough to pull the humidity out of the home.

**Jerry Peck** · 07-16-2018, 01:25 PM

What was the humidity (relative humidity, RH) with the old unit?

What inside temperature did the old unit keep it to (before it stopped cooling)?

Humidity much lower than what you have will likely lead to dry, itchy, flaking skin.

https://www.hvac.com/faq/recommended...ty-level-home/

Donna Brown · 07-16-2018, 03:00 PM

Don't know what the RH was with the old unit...the temp. was kept at 80 degrees, but I didn't need to measure it and didn't have anything to measure it with...until now.

Company just doubled the return air flow by installing another return duct. I cut my dehumidifier off and humidity is already at 43 %. I hate to run the dehumidifier as it runs constantly and is noisy. Humidity outside today is 37%.

**Gunnar Alquist** · 07-16-2018, 04:29 PM

Hi Donna,

Relative humidity and temperature are inversely related. Warm air can hold a greater volume of moisture than cool air can. Humidity is a measure, not of the amount of moisture in the air, but a percentage of the moisture content compared to how much it can hold.

I am not sure if I have explained that adequately.

Look at it this way. As the exterior temperature drops at night (not so much in AZ, but in more humid areas), the "dew point" is reached and dew forms on the grass (or anything that is below the dew point) because the relative humidity has reached 100%. The volume of water has not changed appreciably, the amount of water that the air can hold has dropped along with the temperature.

Consequently, as the air in the home is cooled, the amount of moisture that the air can hold decreases. Living in a home (showering, cooking, breathing) will introduce moisture back into the air. The air conditioner will remove some of that moisture, but not all. In areas with high humidity (Florida, etc.) the volume of water that the air conditioner will remove is high. In areas with low humidity (Arizona, Nevada, etc.) the volume of water that the air conditioner will remove is low. As for expected or reasonable levels of humidity, you might want to contact the installing contractor for numbers.

The links below might explain it better than I can.

https://www.quora.com/What-is-the-re...rease-increase

https://sciencing.com/temperature-am...d-7245642.html

**Jim Luttrall** · 07-16-2018, 07:57 PM

Why did they need to increase the capacity by 25%?
Did it not cool properly on normal hot days?
Did they run a Manual J load calculation as they should?
Almost all 25 year old houses in my area are actually more energy efficient today than when they were built since most have had radiant barrier, insulation, window improvements, it is rare that the house actually needs more cooling capacity.
Unless they put in variable-speed system, they likely did you no favors by increasing the capacity. Since the unit does not run long enough to reduce the humidity, there is no way it can control humidity properly.
Indoor humidity comes mainly from the exterior air but also your activity can influence it greatly.
Cooking, bathing, laundry, potted plants, etc. can all add to the humidity load.
Make sure your dryer exhausts to outdoors and that vents are clean.
Use exhaust fans when showering, kitchen exhaust fans when cooking creates moisture. Hang damp clothes outdoors rather than indoors. Weatherstrip around doors and windows to keep the outside, outside.

Donna Brown · 07-17-2018, 08:57 AM

Originally Posted by Jim Luttrall

Why did they need to increase the capacity by 25%?
Did it not cool properly on normal hot days?
Did they run a Manual J load calculation as they should?
Almost all 25 year old houses in my area are actually more energy efficient today than when they were built since most have had radiant barrier, insulation, window improvements, it is rare that the house actually needs more cooling capacity.
Unless they put in variable-speed system, they likely did you no favors by increasing the capacity. Since the unit does not run long enough to reduce the humidity, there is no way it can control humidity properly.
Indoor humidity comes mainly from the exterior air but also your activity can influence it greatly.
Cooking, bathing, laundry, potted plants, etc. can all add to the humidity load.
Make sure your dryer exhausts to outdoors and that vents are clean.
Use exhaust fans when showering, kitchen exhaust fans when cooking creates moisture. Hang damp clothes outdoors rather than indoors. Weatherstrip around doors and windows to keep the outside, outside.

Not sure what load calculator was used...and the company doesn't seem to want to send me a copy of the report. They did run it twice.

They added the extra air return duct yesterday and I turned my dehumidifier off. With temp set at 78 F humidity ran up to 51%. It rained for 3 hrs also and there was no water coming from the drain pvc pipe. Since it appears to be slanted in an upward position, I'm guessing the water is trapped somewhere along the way. I'll try to attache the picture I took of that....

**Claude Lawrenson** · 07-19-2018, 09:44 AM

Have you considered any thoughts about what human activities taking place in the home? Showers/bathing, cooking, an aquarium, laundry, sealed up windows, etc.

Perhaps the moisture may be trapped in the home due to a number of construction conditions. Again other variables may be the location of the return air system.

Donna Brown · 07-19-2018, 10:00 AM

There are no additional household activities (maybe less cooking).

The additional air return was added because the specs called for a 25 x 25 air return and I only had a 16 x 25. The unit was "clunking" with the 16 x 25 filter at start-up and shut-down....that problem was fixed with the additional air return.

If in fact the drain pipe is slanted upward (as the previously attached pic shows), where is the draining water going? I'm no expert, but I'm thinking that may be the problem???

**Jerry Peck** · 07-19-2018, 11:06 AM

Originally Posted by Donna Brown

If in fact the drain pipe is slanted upward (as the previously attached pic shows), where is the draining water going? I'm no expert, but I'm thinking that may be the problem???

It may, or may not be a "problem", but is nonetheless likely "not in compliance with the code or manufacturer's installation instructions.

Being a "problem" depends on what the rest of the condensate drain line is like.

If the other end of the line is higher, then it may still drain properly ... with "may" being the key word.

Being properly trapped, it is not, however, it is common (at least all around Florida) to run condensate drain line down through the slab, under the slab, then up out of the ground - certainly not done per code or the manufacturer's installation installation instructions, but it has been done that way for decades on all types (brands) of units, and not caused a "problem" as far as the average homeowner knows (it may have cause a "problem" which they were not aware of).

I recently reposted a Trane document about trapping AHUs, and the above practice, and yours, does not meet what "proper trapping" is about.

Donna Brown · 07-19-2018, 11:15 AM

Thanks Jerry, I'll try to get the installation company to check it out.

**Jerry Peck** · 07-19-2018, 11:27 AM

Donna,

This post has the Trane document that explains AHU trapping: http://www.inspectionnews.net/home_i...891#post279891

**Ken Amelin** · 07-19-2018, 04:52 PM

Originally Posted by Donna Brown

How can this be?

I needed a new heat pump this Spring. Was told I needed a 4 ton unit to meet my 1350 sf home. It was put in and immediately started "clunking"....return air opening was too small...adding extra return Monday, today.

I moved to AZ because of arthritis and the low humidity. The old heat pump (3 ton) was fine...no problems with the humidity...it just didn't cool the air any longer after 25 years.

Manufacturer told me by increasing the return air supply, it would lower the humidity in the house.

Can anyone tell me where the humidity is coming from when the humidity level outside is 14?

Thanks,
donna

Not knowing what part of AZ you live in, The average dry bulb temp for Phoenix AZ. in July is 105 degrees F. At 14% RH - the air would have a humidity ratio of approx 50 grains of moisture/ lb of dry air. That same amount of moisture at 70 degrees F. results in approx. 45% RH. Increasing the return air will also increase the amount of airflow across the cooling and helping to dehumidify your home.

**Gunnar Alquist** · 07-19-2018, 05:14 PM

Also, right now I believe the monsoons are coming up from the south. This will tend to increase the humidity significantly.

**Jeff Euriech** · 07-20-2018, 01:46 PM

Donna,

Here is some information to keep in the back of your mind:

We cannot compare the humidity number inside the house to the number outside the house due to the difference in temperature. (Humidity is the amount of water vapor in the air.) If the air is warmer, it will hold more moisture. Fifty percent humidity at 78 degrees inside is different than fifty percent humidity at 105 degrees outside. (Do a search on Google to read up on humidity.)

The humidity level in the general Phoenix area two weeks ago was around 7-10% in the middle of the day. Now due to the monsoons rolling in, I’m seeing 40-60 % humidity if it’s not raining.

Two weeks ago, I saw no water coming out of condensation pipes. Today, I’m just starting to see a little bit of water. Not a steady stream, more like drops of water from time to time.

Now that the monsoons are here, humidity is jumping around a lot throughout the day. It may be dry and sunny in one area and a couple of miles down the road it’s raining.

An air conditioner or heat pump’s primary job is to cool. It’s second job is humidity control. However, a thermostat only reacts to temperature change and not humidity. If the humidity is too high, the air conditioner will not come on.

In the old days, the goal was to keep humidity in the house around 40-45% for the best comfort level. If you are somewhere close to 40%, your heat pump is doing its job.

When I ask air conditioner contractors, if they do Manual J load calculations, they always say “yes”. However, their workers always laugh and walk away.

A 1350 sq. foot house in this area usually has a 3 ton unit. Once in a while I’ll see a 3 ½ ton unit. Never a 4 ton unit. (A 4 ton will work, but will not run as steady as a 3 ton unit. A 3 ton unit will be more efficient and tend to remove more moisture.)

The monsoons are here and normally last through July and August. Then the humidity will start to drop again.

Good Luck

Jeff
Peoria Arizona