I'm going to install a powered attic fan. My attic currently has two small (one square foot approximately) gable vents. I was going to install a powered gable fan system, but has anyone installed roof vents? I live in the North East. Anyone have comments on roof versus gable installation?
Thanks!
Does you have ridge vents and soffit vents now? When you vent the attic, you need a way for the outside air to get in.
No, it doesn't have ridge and soffit vents. It's a house built in 1986. If I install a roof-installed vent, the inlets would be the two gable vents (each of which is about one square foot); if I use one of the gable vents to install a gable-mounted fan (and I intend to install a "system" with fan and louvers), then the sole inlet will be the other gable vent. Unfortunately, this means that all 1500 CFM would have to go through that one-square foot opening. That's why I'm considering a roof-mounted fan, which would provide two inlets for air to get into the house.
I think gable-mounted might be easier to install, but I've not installed either type, so I don't know.
I answered my own question. According to NuTone (manufacterer of attic and other fans), an attic fan needs:
IMPORTANT: For every 300 CFM of fan performance, a minimum of one square foot of inlet space in attic or crawl space is necessary for proper operation. Inlet areas should be located as far from fan location as possible, such as in the eave or side walls.
So, my approximately two square feet (and I'll have to measure this better) would allow me to put up a 600 CFM fan. About the smallest fan I get purchase is about 1050 CFM, which means I'd need about 3.5 square feet of inlet. I might have about three square feet, if my openings are 1.5 by
1 foot. So, I'll need a few more openings.On Thu, 22 Apr 2004 17:10:22 GMT, Bob in CT scribbled this interesting note:
That one square foot of inlet space is net of any screen, louvers, or hardware cloth. If you fail to have enough free space for the fan to draw from it will suck your air-conditioned air from inside your house, into the attic, and vent it for you. How will it do this? It will create a slight vacuum inside the attic and will draw air from around ceiling light fixtures, bathroom vents, and any other small openings. You want to avoid this since the reason for the vent is to keep moisture down and vent the heated air in the attic, thus it will hopefully save on air-conditioning costs. If you draw your conditioned air into the attic you are defeating your purpose.
Good Luck.
-- John Willis (Remove the Primes before e-mailing me)
Install one as exhaust and one as intake. You get a flow across the attic and it works great here in central Florida.
Are you sure your 1986 house doesn't have soffit vents? Houses built at that time should have had attic ventilation done reasonably correct. Without soffit vents, the gable vents are of limited use. The best system is soffit vents combined with a ridge vent. That allows air to move from bottom to top, with no electric fans required.
A related problem is in many homes, the insulation bafoons come in and block the soffit vents by stuffing insulation over them. The correct solution is to install plastic baffles in between the rafters for a couple feet near the soffits. This keeps them open and the insulation out of the way.
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