Dehumidifer for how large area?

Richard · Jun 13, 2009

Waiting for paperwork snafu to get my AC fixed. I have a large dehumidifier. I forget the rating but it was the largest they had at the time (Whirlpool). I think it's 40 pints/day? I don't know how big they go for residential use but when I bought it, it was their largest. 110 volt.

Scenario: AC currently out and dealing with issues on getting it fixed. Meanwhile 2 floors are being "cooled" by simply turning the air handler on to move the air. Basement (1/2 underground) and first floor are both handled by a single AC unit. Each floor is about 1,000 sq/ft. Maybe 1,100.

What I'm wondering is, am I throwing money out the door by plugging this dehumidifier in or would it "help" (I know it's not going to take care of everything) my moisture problem or is 2,200 sq/ft between two floors simply too much for it?

I was thinking on putting it in basement near air handler so as the handler sucks in the air it would hopefully be sucking in some dryer air since the dehumidifer is right there. I could also put it near the 1st floor return vent for same purpose.

Under the logic of the dehumidifier not being able to handle both floors, I've also thought about putting it upstairs (1st floor) so any help it does provide is in the main living space.

I will still keep the air handler on 100% since it mixes the two floors together and keeps the air moving some.

Is this mildly stupid or very stupid?

Mickey_Fx · Jun 13, 2009

IMO the first question is, how bad of a humidity problem do you have? What is a typ RH reading in various locations in the house?

I have a dehumidifier of sim size in a home of about 1200-1300 sq ft. Here, the humidity problem I have in during the winter and not the summer months. My dehumidifier handles the load fairly well. It does require adequate air movement in the house to insure humidity is equalized.

Locating the humidifier close to air intake for your FA heating/cooling system is a good idea. Anything to help distribute and equalize temp and humidity.

The dehumidifier may or may not handle the humidity as well as you like but it could make things a little more tolerable.

RonMar · Jun 13, 2009

40 pints a day is a lot of water to be pulling out of the air.

Like Mickey said, if it dosn't completely do the job, I am sure it will make a difference. Putting it very near the airhandler intake sounds like a good place. The lower humidity air this thing outputs will be distributed throughout the house.

Dehumidifiers are basically an airconditioner with an evaporator, condenser and compressor. Depending on the dehumidifier design, the airflow thru the evap coils(chilled air where moisture is condensed from the air) may be separate from the condenser coil airflow(hot air where heat absorbed from the evap side is discharged). If so it may be possible to duct this warm air outside so it dosn't add to your cooling load. Most designs I have seen use a common fan though, and the airstreams from evap and condenser are combined. Since it consumes electrical power, the net effect is that of a heater...

Sigarms · Jun 13, 2009

Is this mildly stupid or very stupid?

IMO mildly

If you want to take care of humdity (mositure) issues in the home, you can't beat a whole house dehumidifer.

For curiosty sake, I installed one (whole house dehumidifier) when I replaced my first floor system. What I was curious about was the effect this unit would have on the RH levels on three floors in the home, when each floor had it's own seperate HVAC system, and also how it would compare with a new variable speed system as far as taking moisture out of the enviroment.

I'm sold on them now.

So far this year, my first floor temperature hasn't gone below 78 degrees in cooling, even though we've already had some pretty warm days in June now in NC. Third floor during the day doesn't go below 80 degrees, and you'd be surprised how "cool" that feels when it's around 45RH upstairs. I usually run the dehumidifier in June, July and August, and in the other months, the HVAC system can handle the humidity on it's own.

I was pleasantly surprised on the positive effect this unit had on the two other floors where the ductwork from the first floor system was not connected.

Enlcosed are the readings during June of last year when I had the system running (I ran it June, off July, ran it back on in August) to see what the difference would be per RH, Temp, and dew point for each month. Minimum of nine readings taken per day (morning, afternoon, evening), at least one reading per floor for each recording of data (yes, I'm a weanie for taking the time

) Also inlcuding a pic of the HVAC job when it was finished.

Funny, after the first month in June last year when I stopped running the dehumidifier, about halfway into July my wife asked me if I intended on running the dehumidifier in August. I asked her why. She told me she liked it better with it running.

The unit in the picture is capable of doing 90 pints a day. Draws over 10 amps. You don't sell them on cost savings, but on comfort (72 degrees is not always comfortable). In comparison to July with the dehumidifier not running, and relying only on the variable speed system for humidity removal, the dehumidifier makes a huge difference as far as the comfort level. Average an extra $15 per month to run the dehumidifier in the summer months and feel it's worth is for the comfort level.

They can also be run as a "stand alone" unit with no ductwork. Some guys I know use them in crawl spaces for mold issues.

View attachment dehumidifier_readings.pdf