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Ryland 07-16-11 12:05 PM

Cooling the house with the basement.
My house that was built in 1906 doesn't have A/C, last summer we put 16" of insulation in the attic and that helped both with keeping the house cool in the summer and warm in the winter.
We are pretty good about keeping the heat out in the summer, closing windows up at 6am and pulling shades to keep the sun out, but there was a week or so were it was 95F or more in the day time and never got cooler then 80F at night with high humidity, last summer at some point we brought the dehumidifier up from the basement to dry the air in the living space, this worked well but made the living space warmer, so this hot humid weather made me tempted to get a window A/C unit, then my room mates brother, who is a HVAC installer suggested last week that we use the furnace to cool the house with basement air, I've always snubbed my noise at this idea but thought that I would give it a try, so we taped over the safety switch that keeps the fan from coming on if the furnace is open to the basement then installed a twist timer across the two contacts that turn just the fan on (our thermostat doesn't have a "fan" setting) I also installed another air filter to keep dust from the basement out of the duct work so with the dehumidifier running in the basement we are now pulling cool dry air from the basement in to the rest of the house, running the blower for 10-15 minutes is about right, the humidity readout in the basement starts out reading 50% and jumps up to 70% as the air is moved around and takes about an hour or so to get the humidity back down to 50% in the basement, at that point I repeat the cycle.
The theory is that even tho the dehumidifier is warming the air, the basement walls are sucking up that heat, cooling that dry air, it takes time but it has kept our house very comfortable, right now the indoor readings are 77F with 54% and the out door readings are 79F with 84% humidity, the over all feel inside is very comfortable, outside it feels hot and muggy.

NeilBlanchard 07-19-11 03:36 PM

Another way to do this is to have a fan (or fans) exhausting air out of the attic, and close all the windows in the house except one in the basement; and this will slowly pull cool air up through the house during the day.

Close the shades and/or curtains especially on the south and west side of the house (or north and west if you live down under!) to limit the heat build up from the sun.

And yes attic and wall insulation help a great deal, too.

Daox 07-19-11 03:53 PM

Great idea Ryland. Is there any chance we could get pictures and a bit of a write up on how we could do this ourselves? I'm definitely interested. My basement is a nice cool ~50F, and my upstairs is around 80F lately this week!

S-F 07-19-11 04:31 PM

And it's working for an extended period of time? This is fantastic! It's about a million degrees in my house and 99% humidity. Unfortunately the temperature in my basement increased by about 20 degrees the moment I put the insulation up so it won't work for me.

Ryland 07-19-11 06:47 PM

We've had temps in the mid to upper 90's all week and out door temps are only dropping down to the mid 80's, last night it got down to 83F and this idea is starting to fail, up stairs temp is up to 88F at 47% humidity and basement temp is up to about 70F, it is working really well to keep the house dry, even in the mornings when the temp is about the same inside and outside the humidity outside makes the air feel thick and gross, I'll keep doing this but due to the ever rising temps my fridge is no longer keeping it's cool, so I borrowed a window A/C unit to cool the kitchen... trouble is this window unit will cost $4 per day to run so I'm only going to use it as needed.

I don't have a full basement (about 400sf of basement for a 2,200sf house) so I think that a full basement would help a great deal, but keeping the living space at 45% to 50% humidity while it's 70-100% outside has been very nice, but we just don't have the surface area in the basement to cool the air fast enough to combat a week of hot humid days.

I'll do a better write up later, but what questions did folks have, or points that they wanted clarified?

Daox 07-25-11 02:49 PM

What if you ran a fan downstairs just to circulate the air within the basement? I would think that that would improve the heat transfer and cool the air down faster.

I'm most interested in how you seperated the closed loop from itself to make it exhaust into the basement and also suck from the basement.

Ryland 07-25-11 05:24 PM


Originally Posted by Daox (Post 14821)
I'm most interested in how you seperated the closed loop from itself to make it exhaust into the basement and also suck from the basement.

Path of least resistance! I left the filter in the furnace but took the side off the furnace and duck taped a new filter to the side of the furnace to filter the incoming air, so it doesn't pull 100% of the air from the basement, but it's less work for it to pull basement air then it is to pull air from the cold air duct work, I then just left the basement door open and you can feel the draft if you stand in that door way!
I thought about doing something to move more air around the basement, but the dehumidifier is already blowing air around and it takes a while for that to catch up so I figured that it was doing a enough to keep air moving.
The window A/C unit that we ended up borrowing is working really well, it dehumidifies more then it cools and it only takes a few hours to dry out the air in the upper part of the house to 35% to 40% so I'm wondering if it is even worth moving the air from the basement up in to the rest of the house.
A/C unit draws 1,200 watts and dumps all the heat outside while cooling and drying the air inside, seems to drop the humidity by about 20% per hour (not documented, just a guess).
Basement Dehumidifier draws 600 watts while running with the compressor on and drys the air by 15-20% per hour when brought to the main floor of the house.
Furnace fan has a 1/4 or 1/3hp motor and also draws alot of power, not sure how much but I will find out next time I have a clamp on amp meter handy.

So what we are thinking is, this fall when window A/C units go on sale we will look for something like the Haier model that has an EER (energy efficiency rating) of 12 EER while energy star is anything over 9.4 EER, I would then be tempted to install it on either a timer or a humidistat so that it turns off once the humidity is down to a set level in the house, goal being to dry the house out when it's hot and humid, not to get it to feel like a walk in cooler, of course it also seems best to run any sort of A/C at night, when it's cooler and the humidity is at it's all time highest, as the heat is transfers in to air is improved with humidity.

Ryland 07-26-11 05:03 PM

I just checked the amp draw of the furnace fan, 5.8 amps! so it's drawing around 650 watts while it is running! combined with the dehumidifier that draws around 600 watts while running the window A/C is looking like a better and better way to dry our house out.
Of course the dehumidifier keeps the basement dry year round, we have it painted with dry lock paint on the walls and epoxy paint on the floor with plastic in the crawl spaces that is sealed in with spray foam and calk, even with that the dehumidifier runs a few hours per day where before the dry lock paint and crawl space plastic it used to run nearly non stop.

So my conclusion is, if you just want to dry your house out and cool it a tiny bit, an energy star rated window A/C unit really is a good way to go, but if you want to do it on the short term cheap and already have a dehumidifier then using your furnace to cool and dry the rest of your house does work up until that point that your basement warms up, this is of course dependent on the side of basement you have, the size of house and how well everything is insulated.

MN Renovator 09-06-11 05:35 PM

I'll chime in on this. I've seen others do this and so tried it earlier this summer. I didn't use the furnace because at the time it used a motor that sucked about 800 watts or so, I just ran a fan from the basement up to the next level and another from there to the top floor. The basement was about 60 degrees, upstairs about 80, after about 6 hours the house was a uniform temperature, the next morning the basement was 65 and upstairs was high 70's, ran it again and then soon enough the basement was 70 and the upstairs was still hot. The cycle continued until I realized that it wasn't going to work out too well. I usually spend time in the lower level and decided that it was better just to be in the lower level of the house(not the basement) for using the computer, reading the paper, etc. So I let the upstairs be 82 degrees while downstairs was 75 or so and comfortable enough and didn't bother firing up the A/C. I have a guest room downstairs with a bed and ended up sleeping down there and it cut the A/C usage down to days where it was 85 degrees or higher. I also only ran the A/C when the house was going to get above 40% humidity and on the cooler days I'd let it get to close to 50% and allow it to run constantly until humidity was in check again.

I later did a radon test and learned you really shouldn't be sucking basement air into your living areas, especially if you are using a furnace blower to do it, by putting the basement under negative pressure you are sucking air through the small cracks in your basement, the drain tiling, and pulling in air through the soil which is a great way to not only introduce radon into your basement, since you are sucking that basement air throughout the house you are putting that radon everywhere. Western Wisconsin is in an area where if you are doing what you are doing, you really should check your radon levels. My living area including lower level doesn't have much radon but I wouldn't sleep in my basement and I won't be running any fans to push that air upstairs either.

Since hot air rises, I've also been thinking of going the window A/C or mini-split inverter heat pump route too as my A/C is from 1986 and probably in the 10-12 SEER range. I swapped out my shaded pole blower motor for one that is a split-capacitor design and went from 6.6 amps or so to 3.3 amps at air conditioning speed(800 CFM blower at 1/5 HP). More savings at the slower furnace speed when comparing both motors. Either way a window A/C uses so much less power and only cools the area we want it to cool so I think you are going the right route.

Problem is that I don't have the up/down sliding windows, mine are tall side-to-side sliders and I can't find a window A/C to fit them so I'd have to go for a wall A/C which takes me out of the $200-400 or so 10.8 or better EER A/C unit market.

herlichka 09-06-11 06:01 PM

They do make window AC units for horizontal sliders, but for whatever reason they are 2-3 times the money. I have seen them here in Canada at Sears, and this time of year you may find clearance prices!

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