Whole house fans, air condition question , kinda long...

I'm thinking of installing a whole house fan in the hallway ceiling on the second floor. I have two gable vents, one at each end of attic, and my roof has a ridge vent. Would I need to install any additional venting to the attic? What about the benefits, if any, during the summer when I run central air? would this unit help cool the upstairs, or pull all the cold air out? Any thoughts? My other question has to do with central air, I have a two story home, approx, 2100 sq.ft. the first floor stays really cool, but the upstairs is always about 10 degrees warmer. I've played with the vents in the house trying to push more air upstairs then down but it really doesn't help. 2 ton unit, Thanks, Dan
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The amount of venting you need will depend on the fan. It should come with instructions.
As for the AC, a good whole house fan will almost totally negate the value, but not the cost of AC. Remember for every CF of air the fan pulls out, there is another CF of air coming in from the outside somewhere and it is going to be hot and humid as it was outside.
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Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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i can't help you. look at me. i use webtv for krist's sake.
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The fan will come with instructions as to how many square feet of effective vent it needs. You will have to compare that to what you have (prorating the effective area of vents that have insect screening) to decide if you need more.
We generally turn our fan on in the evening when the outside temp has cooled down, then let it run some or all of the night to cool the house and attic. In the morning, shut it down and keep the windows and doors mostly closed, the house will stay cool for most of the day. When the weather gets extremely hot and doesn't cool down enough at night, then we run the AC instead.
The fan sucks air out of the house and blows it out through the attic. You open windows (and make sure the doors to those rooms stay open) to allow outside air to be sucked in. In general it doesn't make sense to use it and the AC at the same time since you will be sucking conditioned air out of the house and blowing it outside. I suppose in theory you could shut off all the AC vents on the second floor, open windows up there and use AC for downstairs, fan for upstairs. But I doubt that would work very well.
If you just want to vent the attic, which would help prevent heat transfer to the upstairs rooms, you could install an attic vent fan in one gable vent. Opinions vary as to whether the attic vent fans are a good idea, however (search this newsgroup for previous discussions).
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Not only that is would likely end up frosting up the coils on the AC or at best make the downstairs cool and clamy.

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Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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roof
Dont know..the total area of the vents, that actually can flow, should match the total output of the house fan..or be damn close.

You mean at the same time as the fan? Never.

Umm...a whole house fan is designed to move air in and out of the home...you crack your windows turn the fan on, and it pulls air from outside, moves the hotter air out, and is similar to a reverse evap cooler...
Also, you are introducing more humidity to the home, as the fans running since you are not allowing the AC unit to do its job, but putting a huge load on it...you NEVER run a whole house fan with the AC on...

Dan..no one here can tell you what that issue is..it could be as simple as you need a service to restore the unit to its working order, or you could have a need where the unit was undersized...the only way anyone can tell is to run a manual D, and J. The J will give the correct unit sizing required for the home, its total area, and location....the D will tell the contractor that is running the J if the duct system is correct for the total BTUs that are needed to heat and cool the total area involved...
Total square feet of the home tells us nothing, as there are NO rules of thumb for AC and heat sizing, and anyone that says otherwise is wrong. TSF is only PART of the formula...you need total area, direction, location, contruction for starters...and no...you cant get all that, post it..and expect a legitimate manual J over the net...

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