View Full Version : whole house fan

John Anderson
06-20-2001, 05:44 PM
Global warming seems to have struck southern CT and one of my customers, well actually it's my wife, is asking me to put in a whole house fan. One of her friends has been telling her how effective they are. The house is a cape with a full shed dormer on the north side. The second floor was finished off with R-13 fiberglass batts in the wall, R-30 in the roof from the eaves to the ceiling, R-19 between the ceiling joists with a second layer of unfaced R-19 across the top of the joists in the attic. Attic vents are rectangular gable vents, approximately 12" x 24". Windows were changed to insulating glass. The first floor is still as it was built in 1958. I would like to know if a whole house fan is a good idea. If so, which kind, (ceiling mounted or gable mounted, is better. Thanks in advance

Rick Hoge
06-20-2001, 09:22 PM

I have many fond memories of the summers I spent with my siblings at my grandmother's home in Greenwich on the long island sound. She absolutely refused to have A/C installed instead relying on the "attic fan" to draw in the cool evening air on still evenings off the water while the tide came and went.

All windows in the sleeping areas were left open after retiring and the whole house was open before. The "fan" was strong enough that sitting on the back porch provided a breeze with the air moving into the home.

I would suggest a fan large enough to move a great amount of air in the geographic location you're in. You might even consider adding a new small dormer(can't tell from your description) on the roof to house the fan and find an area in a ceiling somewhere for a "screened" opening depending on the design of your home. I think it is also important that you consider the fan to be used only with windows open as using it with a closed envelope will only suck air in through any existing soffit-roof-gable vents and possibly make a mess of loose attic insulation and will not accomplish what you're looking for.

Hope this helps, Rick

scott bennet
06-22-2001, 05:59 AM
John: I live in MA and we have a Cape. I grew up in a house with a whole house fan and when I bought my own house (a Cape), one went in. We installed the fan at the top of the stairs of the 2nd floor. There is no door at the top of the stairway to the 2nd floor. I bought the largest one they sold. It works great except when the weather is real humid. Other than that when we get home we turn the fan on and ten minutes later all the hot stuffy air is gone and the cooler evening air is blowing by. You change which room is cooled by opening the windows. If only one window is open, it's like living in a wind tunnel, The fans are worth every penny you pay. The one I've got is two speeds and has a timer. Let me know if you need more info. AC is nice, but the whole house fan is cheaper to run

John Anderson
06-22-2001, 07:51 AM
Thanks for replying. Is there a formula for figuring out how big a fan to get?

Curtis O. Seebeck
06-23-2001, 02:52 PM
I am a custom home builder in Texas and I recommend and install whole house fans in most of my homes. They are wonderful in the evening and can be used at the end of a hot summer day to help cool down the attic as well.

As tothe size to use, I always used a 36" belt driven fan. (The direct drive fans have more problems and are not as reliable.) 36" is the largest that I can easily get. The box says it is for up to 2,300 sf home.

I purchase mine at Lowes here in town because it is convenient. I believe it is made by Certainteed. You can also get them through WW Grainger if you are willing to order it.

They are also great for the times that you accidently burn something in the kitchen and have smoke in the house. Simply open a window near the Kitchen and turn on the fan. In 30 seconds or less all the smoke will be cleared out!

Hope this helps. If you need any more info, just ask.

Curtis O. Seebeck

scott bennet
06-25-2001, 04:50 PM
John: I checked the fan in my Cape. The Cape is 32 wide by 26 deep with a full shed dormer on the back and 2 dog-houses on the front. I have a 36" fan, belt driven. The motor nameplate says it draws 6.7 amps at 115 volts. I believe it was the biggest that was available. The particular one I bought, at Home Depot, is made by Clark United (Dallas TX). As far a sizing goes, I am a firm beleiver of the saying "go big or go home" since a big fan will pull more air thru more windows. You can probably check with the vendor or manufacurer of whereever you're going to purchase yours to get a size recommendation. But I'd still buy at least a 36"

Justin B. Jensen
06-26-2001, 11:36 PM
I would be interested in hearing how the attic space is being isolated from the living space from an airflow perspective. How do you prevent backdrafts from the attic into the living space when the fan is not running and during Winter weather? Barometric louvers? Motorized air dampers?

scott bennet
06-27-2001, 09:11 PM
From an airflow perspective, the attic is totally isolated from the living space except for the fan. The air exits via soffit and ridge vents. There is a pull-down stairway, but that is pretty well sealed with a box with rigid foam insulation and weatherstripping. The box fits over the stairs when they fold up. In the wintertime I move the fan off of the hole in the ceiling it fits over and stuff fiberglass insulation in between the joists. Last winter I had a moisture problem, but I think that's because I didn't adequately attach the vapor barrier (plastic sheet) below the insulation.

Jeff Clarke
06-29-2001, 09:05 AM
No one has mentioned the fact that if your house catches fire while a whole house fan is running, it will burn down much faster.

The way to avoid this is to set up a 110V smoke detector with 4 wire to a signalling relay that cuts power if smoke is detected. I did this myself on our whole-house fan, I think the relay was about $15.00 and the installation was easy. You can test it by pressing the test button on the detector.

scott bennet
06-30-2001, 02:17 AM
That is a good point. Can you provide some details. You mention "smoke detector with 4 wire" - is this a special smoke detector - the ones I have are 3 wires. The smoke detector is wired to the relay which is then wired to the fan. Any details you could provide would be helpful. Thanks.

Jeff Clarke
07-02-2001, 08:51 AM
scott - I should have said 'three-wire' to be technically correct, the ground is the fourth.


scott bennet
07-11-2001, 03:32 PM
Jeff: Do you have details on the relay you used and the wiring details. I'm assuming the signal wire [not the power (black), not the neutral (white), not the ground (bare or green)] is wired to the relay which in turn shuts down the fan when the smoke detector goes off. Any details would be helpful. I like the idea and want to implement it. Scott

Jeff Clarke
07-12-2001, 08:18 AM
Scott - I purchased the relay at a local electrical supply shop - it came with wiring diagram and directions, which were simple to follow. The relay is installed in a 4 x 4 x (deep) junction box, and the signalling leg from the smoke detector (the one that usually sets off the other detectors on the system) is the one to the relay, which acts as a switch to shut down the fan.


Bob D.
07-21-2001, 10:24 AM
Just a couple of common sense points on fan ventilation systems to consider along with the things already mentioned,if refrigant type air conditioning is used also ,it must remove the humidity in order to drop the temperature, so the humidity difference between inside and outside is a factor. Ideally a humidistat in combination with a thermostat should control the air conditioning use.

When using a fan ,opening the inlet areas on the shady side of the structure and leaving the sunny side closed can make a lot of difference and considering the prevailing wind direction and pressure can aid efficiency of circulation.

Location of the whole house circulating fan and air conditioning compressor fan discharges should be planned to dissapate their higher temperature air where it will not be 'short circuited ' into inlet areas. The noise of these fans is another consideration when determining their choice when purchasing and locating them.

The type of fan ,'squirrel cage'open radial or ducted blade' will be more or less efficient depending on the application also.


Scott Bennet
08-15-2001, 08:51 PM

I've investigated relays at my local electrical supply house. I have a FireEx smoke detector. Firex makes a relay for use with their smoke detectors and it provisions for normally closed and normally open use. It is designed, according to the literature, to run alarms, exhaust fans, etc. But it is rated for only 5 amps and the whole house fan I have is almost 7 amps. I'm not sure that's a big deal, but with the nature of the system, a failure could be catastrphic. The counterman at the electrical store said he had a a regular, general purpose relay. It was a Square D single pole, single throw normally closed relay rated for 30 amps. He showed me the unit - very beefy - certianly looked like it should do the job. However, somebody else said that I should be careful, he had heard that incompatible relays would make the smoke alarm hiss and buzz. I email Firex about the issue, but they were no help. Any ideas. Was yours a Firex detector.