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?
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.
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.
(Remove the Primes before e-mailing me)
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.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.