# Attic Fan AND Whole House Fan



## PapaGnome (Feb 15, 2009)

Hello,

I could use a bit of help. I have a new house (Washington State) and it came with an Attic Fan with a 24 hour timer located in the master bedroom closet. I also have a Whole House Fan located in the laundry room with a 24 hour timer. This is a single story house about 1600 SF.

For some reason, I decided to change the times of day and amount of time the fans run for, but the air feels different now. So I decided to search the net for what are recommended settings, but no real luck. Closest thing so far is that when a new house is built in Washington (city/county rule?) that a whole house fan needs to be set to run for 8 hours a day when it is inspected. This of course was done for both the Attic Fan and the Whole House Fan.

It is winter now, and I feel that all heat being generated in the house will just get sucked out by the fans if they are running 8 hours a day (EACH). That is why I adjusted the times to begin with. However, the air just seems different now and I actually feel colder in the living room after work. Possibly because I have both timers set to start moving air when I get home.

Here are a few questions....
1) What is the purpose of having an Attic Fan, and for having a Whole House Fan?

2) Should these timers be adjusted by the amount of time they are running, and how often apart during the day they run; based on whether it is winter or summer?

3) Are there some recommended times of day and the amount of time that each of these fans should be running?

I could always call the people who installed the fans/timers and ask them what the settings were when they install them, but I would prefer to understand how these fans work and why they are on timers.

A gal I know whose husband built their house said that after the inspector passed the house, they just shut off the breaker to the Attic Fan. The whole house fan (similar to our location of the laundry area in a single story house) she kept as her husband set it up.

Does anyone here have experience in Washington or colder climates and why 2 fans are put into new construction?

MY GUESS from what I have read and think to understand. The attic fan is suppose to exhaust air out of the attic. The old days (when houses were not sealed tight like they are now) they would take air from the house and vent it to the attic. Now I see most posts and web articles describing attic fans as a way to keep a house cool in the summer. The limited articles I find on attic fans and the colder climate here indicates that the attic fan might be needed to keep mold from growing in the attic and to keep the air moving so no condensation is building up. Now the whole house fan is to get rid of all the bad air in the house. Perspiration from body sweat, stagnant air from odors, and by opening up the windows to bring fresh air in, the whole house can exchange the bad air with fresh air. BTW, the windows in this house have these little flippers that allow a small amount of air to come in from the outside without actually opening the windows up.

And my quest to find out and understand how these fans are needed and how best to operate their timers in my area is on. 

Tim


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## hvac122 (Dec 10, 2007)

Not sure on Washington laws. I can tell you this. Unless every penetration into the attic is sealed the attic fan is the worse thing that you can have installed. This means all wire holes plumbing holes etc. need to be sealed with spray foam. Otherwise the heating and cooling you are paying for will be sucked out of your house. I would turn the breaker off to that fan. A whole house fan is ment to be run in the summer when air conditioner is not in use to help cool the house. Personaly I would not have one of those either.


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## hvaclover (Oct 2, 2008)

It's obvious that since whole house fans pull out huge volumes of air that you would not want to run either while heating or cooling the home.

During a heating cycle with whole home fan operation the furnace fumes will not flow up the chimney but will pull them back into the house. CO poisoning will be very fast.

During cooling the already cooled air will also be sucked out and the ac won't be able to keep up the the amount of air being sucked out by the fan.


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## yuri (Nov 29, 2008)

I would imagine they have a fresh air/makeup pipe to prevent negative pressure. We have these whole house fans in place of bathroom fans and for ventilation. Ripped mine out and put in a Lifebreath HRV instead and love it.


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## Yoyizit (Jul 11, 2008)

I put a downstairs-accessible lighted switch on my attic fan to override other switch settings, so I can pull cold air into the attic in winter to prevent ice dams, when they are likely.


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## PapaGnome (Feb 15, 2009)

Further information....

Single story, new construction, only 2 months old, house is sealed pretty tight I think, spray foam was used in the walls when wires/pipe were installed, electric wall cans for heat (240v line volt heaters) in each room.

I think the house is well sealed as I watched it being built and think on that front, it is tight.

Turn off the breaker for the Attic Fan? Sounds so simple, but why install the Attic Fan and set the timer to 8 hours a day operation when I took possession? There must be some reason for this fan to be installed and set up; even though it is winter time.

This house has no air conditioning (Washington State, it is not needed for the 9 days of good weather we get each year) and only electric appliances; no gas.

I do not see a fresh air makeup and there are no pipes for that, however the windows do have these little vents that you flip open and fresh air will come in through them. These flippers on the windows are about 12" tall along the window frame and when flipped open, allow about a 1/4" gap where air flows from the outside into the house. Is this considered the fresh air makeup?

From memory here, but the Attic Fan has a switch in the attic that is always on. Then from there it is wired down to the master bedroom closet with a 24 hour timer. That timer has settings to go off 4 times a day and you can set how long it will run. There is also an overide button on the timer so if you want to manually start it before a scheduled time.

The Whole House Fan, in the laundry room, only has a timer with the manual overide start button. 


Yoyizit says;
"I put a downstairs-accessible lighted switch on my attic fan to override other switch settings, so I can pull cold air into the attic in winter to prevent ice dams, when they are likely. "


How often do you do this? Should I set my timer to run during some time of day/night to prevent ice forming in the attic? Weather has been about 40 degrees here during the winter.

I wonder if the Attic Fan is really only for keeping moisture from building in the attic when the house is built tight. Since I have a whole house fan, it can exchange the house air at any time I set it. However the attic fan, if the house is tight, won't be able to grab air from the house below the roof line as there is no leaks and/or holes for air to push up through.

Tim


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## Yoyizit (Jul 11, 2008)

_Yoyizit says;
"I put a downstairs-accessible lighted switch on my attic fan to override other switch settings, so I can pull cold air into the attic in winter to prevent ice dams, when they are likely. "


How often do you do this? Should I set my timer to run during some time of day/night to prevent ice forming in the attic? Weather has been about 40 degrees here during the winter._

As it happens I've never done it. 
We had only one winter where everybody in Southern Montgomery County was having ice dams and by now my fan doesn't work anymore. 
Your roof and house has to be of a certain construction for the water above the ice dam to drip onto internal drywall.

BTW, Leaving windows open makes it less likely that your fan will steal Combustion Air from gas burning appliances. Use a candle flame to check, but this may not be a foolproof test.


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