Lowering Humidity in House - Have AC

[SJay3660]

I have a 2500 sqft house with a basement. It is a 2 story with the upper story open to the lower story (Open balcony).

I know my air is over-sized and replacing it is not an option.

I can get the temp down fine (70 degrees) but the humidity is always around 54% to 61%.

Would I really notice a difference if I put in a whole house dehumidifier?

Would the house feel more comfortable?

Anyone install one and you are really glad you did?

Thanks
Steve - Mid-Michigan

I would install it with its own return on the 1st floor and then send the conditioned air through the supply side of the furnace duct work. I would only run it when the AC is off.

 

[Showkey]

50-60% indoor humidity is totally normal. (summer)
30-50% indoor humidity is normal in winter.

These numbers vary with outside temperatures.
-10* Outdoor winter temperatures and 50% indoor humidity will often generate the concern my windows and doors a sweating or frosting/icing.

Run a dehumidifier in the basement might help.......but.........basement humidity level is considered perfect at 50%. Or at least a reasonable goal, dry enough at a reasonable cost. Basement levels consistently above 70-75% are when bad things really happen like mold, mildew, funky smells etc. First noticed on organic materials like paper, leather, fabrics.

Running a whole house dehumidifier and not running the AC would be counter productive. Plus running either would require the windows and door to closed.
It is common to run a basement dehumidifier and not run the AC, with the up stairs area windows open in the upper Midwest climate. Especially when the hot humid days are gone.....like next week.

 

[mike93lx]

I agree, your quoted humidity numbers are fine to me. My house is 52% right now in the main area, and is often in the mid to high 50's. I also never cool anywhere near 70. My main a/c is set to 75 at the lowest, usually 77. Feels very nice and my wife complains it is too cold regularly

What is causing your concern?

 

[yeldogt]

My guess is the humidity level is higher than what you are measuring.

I set mine for 50 unless it's cooler out -- then I shoot for 48. When the numbers get into the upper 50's -- would be way too high.

When I was started a major overhaul of the house I'm in now -- the main part was covered by a 4t unit ... We upgraded insulation and windows .. the summer before the place was expanded we had to drop it way down. Sometimes to 68 when lots of people came over just to keep the humidity in check ... it was not ideal. It's now a bigger house with a 3T.

There really is nothing else to do -- I normally add a ducted one in my old house retrorationa because they leak and you get humidity.

Do you have control of the fan in the unit -- how many speeds?

Some of the 4 speed fans can run on #3 and work better for humidity control -- also the dehumidifiers can trip the system to low fan to move the air around

 

[SJay3660]

I turned down the speed of the fan a few weeks ago which did help.

I would like to keep the humidity at around 50% and under. My AC is a 4T but should have be a 3.5 - I screwed that up 3 years ago. Don't want to spend a bunch of money switching it out.

Normally only run the AC about 15 - 20 times a year. This summer has been unusual.

I think it is just my OCD and my obsessing over it.

 

[Showkey]

The other wild card in humidity is the occupants and activity level:

Number of occupants
Activity level of the occupants
Pets
Coming and going
Laundry
Cooking
Showers
Use of ventilation and air exchangers
Proximity to a body of water

Leave the home 24-36 hours it’s amazing how the numbers change.

5 point spread is noise on the readings.

 

[Terry D]

Those humidity readings are fine. You need some humidity in a house or things will start to dry out. Does you house feel humid. Maybe the meter your reading it is not correct. Is your AC short cycling. How long does it run each time. Is there condensate coming out of the drain. Proper air flow across your A-coil is important, to much air flow, and it will not remove the humidity correctly. The instruments to read CFM cam be expensive and are not common for the average home owner. You may have to have a professional read you CFM. You are looking for 350-400 CFM per ton. Another measurement you can take is the Delta T, that is the difference in temp of the return air entering you A-coil and the supply air exiting the coil. These measurements need to be taken at the unit, not at the registers. I usually drill a small hole in the supply and return duct at the unit for the probe, and just put a sheet metal screw in it when done. You are looking for around 18 to 22 degrees difference, some units could be lower than that

 

[brewchief]

I've installed a bunch of the Aprilaire whoke house units, almost always the 1830, the larger units do work better but they do make more noise. Simply lowering the basement humidity can have a significant impact on the whole house, we have several people here at my work with the 1830s in the basement without any ducting and they all love them.

Was the furnace replaced at the same time as the A/C? If so does it have a variable speed blower? Most of those can use a thermostat with dehumidifier controls and drop the blower speed further when humidity is high.

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[Showkey]

Problem solved.......the weather changed

 

[fitter30]

Running the ac only part time can defeat the purpose of lowering the RH. Open windows and humidity is pulled into the house. High RH flows to low RH. Bathroom exhaust fans need to run at least 20-30 minutes after a shower. Hows the weather stripping around the windows and doors. Tighter the house less RH transfer. Dehumidifiers are rated differentially. Box store dehumidifier rating at 80*@95% RH. Crawlspace/ ducted dehumidifier have a certification rating AHAM 80*@ 60%. All dehumidifiers when lowering the operating temp or RH performance drops at 50* they do very little.

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[Showkey]

Running the ac only part time can defeat the purpose of lowering the RH. Open windows and humidity is pulled into the house. High RH flows to low RH. Bathroom exhaust fans need to run at least 20-30 minutes after a shower. Hows the weather stripping around the windows and doors. Tighter the house less

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This was discussion on Primarily the upper Midwest part time use is the norm?........where many people use the AC between 15-40 days over the entire cooling season. Some years as little as 7 days old of AC use. Many of these areas see 10-15 days with plus 90* the entire year.

The use of the AC is on very warm (hot) say 90*+, hot and humid days 90* 70% humidity and warm 85* and 85% humidity.

At the same time it is very common to run a dehumidifier in the basement from Memorial Day to Labor Day continuously.

Example

0 days above 90*. 2008, 2014, 2017
1 day above 90*. 2015, 2019

 

[yeldogt]

There is nothing you can do if you have high humidity inside -- other then remove it.

My multi speed compressor has eliminated the need most of the year in the house that had one before the unit went in ... I debating the need n the current one .... but will most likely use as I need some make up air and I don't love the HRV's

 

[LS6 Tommy]

I would like to keep the humidity at around 50% and under. My AC is a 4T but should have be a 3.5 - I screwed that up 3 years ago. Don't want to spend a bunch of money switching it out.
I think it is just my OCD and my obsessing over it.

You'll never get really low RH with an oversized unit. It won't have a long enough run time to dehumidify properly. The RH numbers you have now are pretty good, especially for an oversized unit.

Tommy