Dehumidifier, Air Conditioner, Air-To-Air-Exchanger

June 1 2005 to June 24 2005

Pictures of dehumidifier, and digital humidity guages, below.

My house was estimated to need between 1.5 ton and 2.0 ton of air conditioning (19700BTUs). Normally HVAC professionals select the lower value, so that the air conditioner will run more and cycle on and off less. Running longer has the dual advantage of not starting (which uses more electricity), and removing more humidity because it's constantly on. One of my neighbours has an air conditioner that's running 24/7.
But I've had a 1.5ton air conditioner, and it previously wasn't enough air conditioning in the summer to cool my home on several days, and the upstairs was too warm to work in in the summertime, so I moved into the basement.
With the new 2.0 ton air conditioner, and a more powerful fan in the new furnace (to blow the cool air upstairs), my whole house is always a comfortable temperature. Equally importantly, if it's hot outside and I turn the temperature down, the house actually gets cooler! With the old air conditioner the house would only get cooler at night, and it was iffy as to if it could hold the temperature throughout the day.
I leave the furnace fan set to 'automatic' rather than 'full time' on the furnace, as this seems to reduce the humidity.
My thermostat has a 'humidity' ability which will run the air conditioner longer if it's needed for high levels humidity, but stops if the temperature is 3 degrees below its setting. This proved insufficient last year.
All three floors of my home are fairly close to 24 degrees C now (75F).

I also have an air-to-air heat-recovery-ventilator (aka heat exchanger). I've found that in the summertime, that the warm moist air outside, when brought inside where it's cooler, dramatically raises the humidity.
So I have a timer on the air-to-air, so that it runs from midnight to 6am.

I had a big problem with humidity. Last year I started measuring it.
On 2004/08/12
- RadioShack guage said 42% in basement
- Bioaire guage said 46% in basement
- LaCross 42% in basement
- Lennox 39% on first floor
- Accu-Temp mechanical hygrometer 70% (I've since thrown this guage out)
- DIY Psychrometer said 53% (dry bulb 21.5C, wet bulb 15C)
Now those numbers don't look all that high, but I can tell you it was humid, and smelled musty in the basement, and bathroom towels took longer to dry, so I decided they weren't measuring humidity accurately.
Relative Humidity recommendations:
- lots of places say: 30% to 50%
- Rod says 35% to 40%. Below 35% you get dry throat, and above 40% (well 50%) you invite mold growth.
I tried a Simplicity Dehumidifier model 43-5401-4 28 pint portable from Canadian Tire -- and it was noisy and didn't solve my humidity problem. It's currently disconnected and in it's box.

A few weeks back I picked up two Maytag 65 pint M7DH65B2A 115V 7.4A dehumidifiers from home depot.
I bought one for the basement and one for the top floor. This was silly because cold (more humid) air falls, so the one upstairs never turned on. About three days later I moved the second one down into the basement and plugged it in next to it's neighbour.
One running makes 65dB(C slow @ 1m) of noise, and 67dB(C slow @ 1m) when both are running together.
They seem to run a lot. I don't have stats on the electrical usage yet.
They work great. Humidity problem solved I think.
Over the past couple of weeks we've had several days hitting 32 degrees celcius (90F), with 80% to 95% humidity outside. Yet the humidity inside has always been comfortable.
They have a drain hose output ability, which I've got running into a floor drain so I never have to empty the buckets
I've also noticed that there seem to be fewer bugs (centipede like things) in my basement than last year, but the year isn't over yet. Maybe they just got tired of me killing them and left.
I initially set the Maytags to dehumidify at 35%, which is their lowest setting
On 2005/06/06
- RadioShack guage said 32% to 35% in basement
- Bioaire guage said 34% to 39% in basement
- Maytags say 30 to 40% in basement
The maytags seem able to keep up with the humidity, even though it was 30C outside at 90% RH, inside was 24C and 35%RH to 40%RH and the maytags weren't running constantly (i.e. they did shut off occasionally during the day) and I had the air-to-air running constantly which had to be pumping in humid air (hot high humidity air, cooled as it's brought into the house, gives really humid air into the house, even though the air-to-air has a condensate drain)
I've since set the Maytags to dehumidify to around 40%, which seems fine. No musty smell in the basement. People comment on the comfort of the house.
On 2005/06/24
- RadioShack guage said 37% in basement
- Bioaire guage said 40% in basement
- Maytags both say 40% in basement
- LaCrosse says 34% on first floor
- Lennox says 35% on first floor
(these numbers move around a lot, the maytags bouncing as much as 15%, the others as much as 5% -- unlike the thermometers which are +- 2 degrees, nevertheless humidity is fine)

The maytags never seem to agree on the humidity. Nor do they seem to start relative to what humidity is shown, except in the most general sense.
So all four possibilities happen
- both off
- right one on, left one off
- right one off, left one on
- both on
Similarly, for their humidity reading, all three possibilities happen
- both same
- right one lower, left one higher (by as much as 15% difference -- even though they are inches apart)
- right one higher, left one lower

Well I finally got my electric bill.
June/July2,500 kWh2,700 kWh3,100 kWh
Aug/Sept2,600 kWh2,300 kWh
So I suspect that these Maytag Dehumidifiers are using about 200 kWh per month. Or about $21 canadian per month to dehumidify my house. (5.8 cents per kWh plus delivery plus two other charges)
Now it might be less than that, because my thermostat computer refused to program (or display the temparature) for the month of July 2005, but it still managed to run the air conditioner at its programmed setting so I was keeping the house two degrees cooler than I normally do in the summer, and thus the running of the air conditioner may have both been more electricity to run the air conditioner, as well as the cooler air forcing the dehumidifiers to run more.

Click on the pictures to see bigger ones
15% difference
drain hoses
35%, 39%, 39%, 50%
34%, 35%, 37%, 40%
Hearing protection, sometimes worn when the dehumidifiers are on.

Links to last year's questions on these topics:
- Air Conditioning BTU, Acoustics and Humidity
- AVS Forum: Humidity in basement more than 60%