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jmd494 06-03-2010 07:24 PM

Whole House Fan - Creative Ventilation Solution or Bad Idea?
I'm new to the forum so hello all...glad to be here. I recently purchased a 6,000 CFM whole house fan for a 1,500 square foot town house.

After doing some research), I realized I a 6,000 CFM fan need 1,152 square inches of Net Free Ventilation Area (NFVA) in the attic (i.e. 1,152 square inches of ventilation). I only have ~650 and, according to my HOA's rules, adding gable/roof vents is not an option.

To the Point:
I have a large spare bedroom that is not in use. It has two large closets and two windows. My plan is to increase my ventilation by installing one 256 square inch register in the ceiling of each of these closets.

Something like this:

When the fan is in use, I will open the windows in the spare bedroom and close the door, thereby transforming its windows into exhaust vents. When the fan is off, I will simply close the registers.

Would this be a good idea? Or should I just cut a big hole in the drywall separating my attic from my neighbor's and double my ventilation? (kidding! :D)

Wuzzat? 06-04-2010 07:42 AM

Watch out it doesn't steal combustion air from your appliances.

jmd494 06-04-2010 08:44 AM


Originally Posted by Wuzzat? (Post 45359)
Watch out it doesn't steal combustion air from your appliances.

Sorry. That went right over my head. Can you elaborate?

TxBuilder 06-04-2010 12:24 PM

He's joking. He's saying it's going to suck all the air through your house. I think. I have no experience with these. Sorry.

inspectorD 06-04-2010 04:54 PM

there are a couple different camps on attic fans, or whole house fans, or whatever ya'll call them whereever you live.
The issue you explained is right on, if you do not have the area to remove the air from the attic, it becomes a positive pressure and you can find all kinds of insulation fibers, mold in the insulation and little pellets comming throw the fixtures.... blowing around your home...not good. Through light fixtures, other bath fans ect...
The other issue you can do is create a backdraft on your oil or gas fired water heaters and boilers that heat water indirectly.
I tell folks to get a roof vent near the fan and install the size you need. They look like spinning turbines. And set the fan on a timer so you do not create a large flue gas backdraft. Set for 20 minutes and open all the windows.

Good luck.:D

oldognewtrick 06-04-2010 07:10 PM

jmd, why don't you just take the vent back and get a smaller size? And please don't cut the dry wall in the attic, cause it's probaly a fire wall.

woodchuck 06-06-2010 07:10 PM

If it's a two speed fan keep it on low. How about eve vents.

Patriot68 07-01-2011 06:03 PM

You are way oversized by 4x...I have a 1500SF TH as well and you need a 1500 CFM whole house fan...2000 CFM MAX...go to the Air Scape website and they have a calculate function (not a rep, just an easy function to use). The 6000 CFM WH fan you are trying to use will cause you many headaches that are not even worth going into. If you have a ridge vent and roof vents already you may not even need to add more vents if you right size the WH fan. If you have to add vents another option is to add a solar powered attic fan...yes, whole house fans and attic fans are two different items. If you have a gable vent (HOA does not have to approve as it is internal) you can add an attic vent there and it will increase the discharge and balance the attic space.

fixitrght 07-01-2011 07:11 PM

I'm interested to hear how you solve the problem, because I don't know anything about installing whole house fans. Matter of fact I only know one person with a whole house fan and it was installed when the house was built. I would think the best solution would be to take it back and try to get one that is the right size for your townhouse. Good luck! Let us know what transpires.

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