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Cooling the Attic

During the summer month the evening air outside is much cooler than the inside air. That is because the blazing sun bakes the roof and the attic during the day. At night, the heat trapped in the attic radiates down to heat the house. So one way to cool the house during the got summer month is to cool the attic. It would be very nice to draw the cooler air from the outside to cool the air inside.

One amazing method to, not only cool the attic, but to suck in cool air into your house is to install a whole house fan (see diagram below). The whole house fan moves air from your living space into the attic, and out through the vent. This circulation also sucks cool air from the outside into your living space. It is really a simple and efficient technology. Although it is really not that hard to install a whole house fan, I am just not ready to put a big hole between the living area and the attic. For now, I will stick to cooling the attic.

Attached Image:

Whole House Fan Diagram.png

Chieh Cheng
Sun, 06 May 2007 11:20:34 -0700

For this project I bought three Lasko Weather-Shield 20" Box Fans with Thermostat. This fan has three speeds plus temperature control. The temperature control allows the fan to turn off when the attic is cool enough. But that is not sufficient, because when the air outside is hotter, there is no point to turning on the fan. Therefore, during the day, the fan should be off. So I got a few Intermatic TN111GC Lamp and Appliance Timers (same as the RadioShack 61-1068 Mini Lamp/Appliance Timer) to turn on the fan at dusk.

Two of these fans will go into the attic, facing out on the larger attic vents. The fans will blow hot air out, which will cause cooler air to be drawn into the attic. The third fan will go into the garage attic, to blow out the air from the front house vent.

Chieh Cheng
Sun, 06 May 2007 11:37:46 -0700

wow. this is awesome!

how much do you think you'll save with respect to to the AC portion of the electric bill?

Mon, 07 May 2007 14:19:39 -0700

Well, let say I run 3 fans from 4 PM to 1 AM every day, that comes out to be 270 hours for 30 days. And based on the lowest setting on the Lasko box fan, it uses 61 watts. And using the Generic Electrical Energy Cost Calculator, I got $4.92 per month. (Since the calculator doesn't have the Lasko fan, I used 3 60-watts light bulbs for 270 hours).

The same calculator showed that running "Window Air Conditioner @ 12,000 BTUH" for 100 hours costs $12.14. So if you run the same AC for 270, it would cost $32.778.

You probably can't substitute fans for AC. But you can offset the AC cost by using more fans . . . Exactly how much you save depends on how much AC you use during the summer month.

In my situation, I'm only trying to be more comfortable, not saving money. My summer electricity bill is actually quite low, because my wife hates AC. She doesn't hate the cost (I hate the cost), but she hates the feel. Last summer, she rather wear less in a 90 degree home, rather than turning on the AC. My hope is that with these fans, I could cool the attic way down. I'm hoping to bring the house down to comfortable level with no AC or just a little bit of AC.

Chieh Cheng
Mon, 07 May 2007 18:24:45 -0700

I was able to mount the garage fan last week. I've noticed that my garage is no longer hot after dusk. The garage is pretty close to the outside air temperature after the fan is running for two to three hours.

Tonight, I had the time to climb up to the attic to install the other two fans. When I went up into the attic at 8 PM, I noticed that the attic is not all that hot either tonight. Usually the attic is still hot in the wee hour of the night.

There is a small rectangular whole between the house attic and the garage attic. I suspect the air circulation caused by the garage fan is cooling the house attic as well. Because the attic was quite cool, even though outside temperature went up to 102.9 degrees today, I'm starting to think that running the fan to 1 AM might be overkill.

Chieh Cheng
Fri, 11 May 2007 00:14:56 -0700

Can you provide some temperature information?

With the temp cooling in Southern Cal in the next few days, It'll be ahrd to see but I really like to see how things are day to day when temps are in the 90s.

In Pasadena, we can get quite hot too.


Fri, 11 May 2007 08:31:47 -0700

Actually, I've also thought of measuring the temperature with and without the fans. Not sure when that's happening though, because I'll need two full days to measure temperature every hour. It's find to find two full free days nowadays.

Chieh Cheng
Fri, 11 May 2007 08:39:28 -0700

I live in south Texas and was able to do a similar job passively. I added soffit vents around the house and attached garage, I think there is 39 of them and I want more, also I built a 3 x3' cupola fully vented on the main house and a 2x2' on the garage. It gets to 100' F in the summer, the attic peaks at 110, and when it cools off the temperature tracks the ambient down immediately saving having all that heat stored up all night and radiating into the house. I want to custom build a roof ridge vent to add to it, the commercial vents may be ok for venting moisture but they don't keep up with the heat

Bill Watson
Tue, 26 Jun 2007 16:04:45 -0700

Those fans appear to be portable household fans. It is not likely that they are approved for permanent installation in an attic. You should have used gable fans.

John Grabowski
Fri, 29 Jun 2007 03:14:00 -0700

You must be doing something right, Bill. I have soffit vents around all around my attic. But it doesn't seem to bring the attic down to the level I desire. I'm wondering if the vented cupola you put in is the driving factor.

John, you are probably right. The fans I put in aren't permanently installed at this point; it's only mounted with a few heavy-duty wood screws and bungie cords. I just wanted to see if it makes a big difference before I shell out the money for the real thing.

So far the fans seems to be working well. If it continues to work well over the summer, I will most likely shell out the money for a solar powered gable fan for next summer.

Chieh Cheng
Fri, 29 Jun 2007 11:14:17 -0700

I would be interested in hearing your results with the solar powered fans. Some of my customers have asked me about them and I have no idea whether they work well or not.

I'm glad to hear that the attic fans are only for research. :)

John Grabowski
Fri, 29 Jun 2007 14:42:41 -0700

Sure thing, John. I will continue to post my progress here in the future.

Chieh Cheng
Fri, 29 Jun 2007 16:50:41 -0700

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Title: Cooling the Living Space
Weblog: GearHack
Excerpt: Now that I have started cooling the attic, it's time for the second phase to convert my house into a more energy efficient home. In this phase, I want to circulate the cool air outside (after dusk) into the house, while forcing hot air inside the house out. Even though I did not implement the whole . . .
Tracked: Fri, 11 May 2007 00:48:53 -0700

Title: Tips on Keeping Your Home Cool During the Summer
Weblog: GearHack
Excerpt: Heat comes inside through walls and ceiling. So, it would be a good idea to water the terrace just before noon. Get some old cloth sacks, wet it and place all over the terrace. This will retain dampness for a long time. Water them each day in your spare time.
Tracked: Tue, 11 Aug 2009 20:40:07 +0000

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