On Thu, 27 Apr 2006 22:31:39 -0400, "Walter Cohen"
Your question makes sense but I can't answer that without knowing more
facts. Probably best to ask some local a/c guys where you are. Maybe
another thing to consider is a roof ridge vent tho its probably more
economical when you are replacing your roof.
I'm coming in in the middle of the thread. I have an unfinished attic
with no window, and a trap door between the attic and the second
I love my electric roof fan. It took 10 degrees off my second floor,
and the townhouse already had full width soffitt vents front and back
and a full width ridge vent. I don't use AC at all normally, live in
Baltimore, and when I bought the house the first summer, it was too
hot to go upstairs at all after work. I would sleep in the basement
and go upstairs in the morning to wash and get new clothes. After the
fan the upstairs was usable to change clothes, watch tv or work at my
desk, and sleep. A couple weeks a summer are still pretty hot.
The fan keeps the attic from ever gettting that hot. It goes on
around 10 or 11 in the morning and turns off between 6 and 10PM, so it
makes no noise when I'm trying to sleep.
There is so much circulation now that after 15 or 18 years I found a
layer of "lint" on all of the soffitt vent screens, like one find on a
clothes dryer screen but not nearly as heavy. None of my neighbors
had that. I peeled it off.
It's possible I need more insulation in the attic "floor". The
fiberglass only comes up to the top of the joists, and I thought that
was enough. I have to get more info about that.
If you refer to an attic fan, some will think you mean what others
call a whole house fan, a fan in the ceiling of the second floor, that
only works when it has gotten sufficiently cool out side, and which
some use while they are sleeping. Too much noise.
They get installed on LOTS of homes along the Gulf Coast for that very
reason, to help pull air OUT of a HOT attic. For Attics, ridge and
soffit vents seem to be a better solution to that problem,
In NY, you will need a way to wrap the turbine in the winter, and/or put
up a interior barrier to keep the cold winds out.
"Depending upon the diameter of the vents and the wind speed outdoors, the
turbines can expel vast quantities of humid air...
"A small 12 inch diameter turbine vent with a constant wind speed of 5 miles
per hour (mph) can remove 347 cubic feet of air per minute (cfm) from the
attic space. A single 14 inch diameter turbine vent that is subjected to 15
mph winds can expel up to 1,342 cfm of air!
"If the winds are still, the vents still allow air to drift up and out of
the attic space..."
A roof turbine operates at no cost, requires zero maintenance, and lasts for
many, many years.
In order to exhaust the air, there has to be some way for fresh air to
enter. You can't have too many soffit vents.
A whole-house attic fan needs to exhaust 4000 cu ft / minute (for a 1500 sq
ft) house for most efficient operation. A mere THREE 14" turbines would be
sufficient to air out a whole house (at an ambient wind speed of 15mph).
Obviously, then, turbines are a cheap, easy way to prevent the attic from
turning into an oven.
Well yes and no. As another poster said, for winter, you will have to
have a way to cover it or cut off the circulation so the cold air
doesn't get in.
I've had some (turbines) on my Gulf Coast homes and I can't say they
are that great. I suppose they helped to some degree but my attics
still got hot (in every home that had them). Now I see more new home
construction using ridge vents with soffit vents instead of the
Just in case, if his neighborhood has a home owner's association, he
might have to check to see if the deed restrictions allow turbines.
It happened to me once where the restriction allowed it as long as it
was not in view from the front. I don't believe this is common tho.
Nonsense. We have 35 below winters and I have never seen a turbine covered.
If it's venting an unheated space blocking it is down right dumb. It still
removes moisture from the space during the winter.
On Sun, 16 Apr 2006 16:39:23 -0700, firstname.lastname@example.org wrote:
Funny but I HAVE seen them covered on the outside and it's possible
that even those not covered might have had some covering / blockage
from inside (dunno because I can't see the attic of course). I agree
that if you don't care about cold air getting inside, then no need to
do anything. And usually moisture isn't a problem in winter for
<rob> wrote in message> Funny but I HAVE seen them covered on the outside and it's possible
You are misinformed about moisture not being a problem in the winter. When
heat escapes from the thermal envelope into an attic, it must exit, or you
get condensation in the attic. It is simple physics of when cold meets
warm. Take for example a glass of ice cold liquid, sitting on a coffee
table at room temperature, it's not leaking fluid from the glass, but
I have seen instances where homes had power vents and that's all. The
problem is, they don't come on in the winter. This caused thousands of
dollars worth of damage to the roof deck, insulation & wallboard.
Never block venting during the winter, unless you want condensation, rot,
This link will provide you a better explanation on how a house breathes.
I agree and I should have said it differently.
I was thinking that usually you wouldn't bother to cover up the
venting unless you had a heated (finished) attic so moisture shouldn't
come about unless the venting was inadequate in either case.
That's why the roof fan that I bought 23 years ago urged owners to
install a switch on the floor below, so they could turn the fan on
after a hot shower or something that put humidity in the attic. They
also urged people to install another switch to turn it off, when the
thermostat would turn it on.** They gave a wiring diagram, very
simple to use. I used one of those double switches on one box, but
mounted the box sideways, so the switches would be up and down.
**I use that in the early spring and the late fall to warm my house
with the daytime sun.
"Ventilating attic spaces in winter months is often more important than
venting them in summer.
"Water vapor from the inside of a home can drift up and into an attic space.
If this water vapor is not quickly exhausted to the exterior atmosphere, it
can often condense upon the cold roof framing members and the underside of
the roof sheathing.
"It can get so bad that water can drip from the underside of the roof and
when the temperature gets low enough, frost can actually form up inside the
attic. Moisture conditions such as this can lead to wood rot and mold
My house has both: A ridge vent AND four 14" turbines (3000 sq ft).
Agreed. I don't think one should cover them up unless the attic is
finished and heated. For some reason, I was thinking of a finished
(heated) attic in my original post but didn't say that so it was a
misleading statement and not applicable in ALL situations.
On Sun, 16 Apr 2006 14:21:07 -0400, "Walter Cohen"
For the record, I live in the tiniest valley. The stream is only 1 or
2 feet deep and only 6 feet across most of the time, and the valley is
only a half mile to a mile wide and 30 feet deep, I think, so it is
pretty shallow. There are big trees on two sides of me.
And I get almost no breeze most of the time.
Before relying on wind to turn the turbine, check if there is wind.
If the turbine costs so much money, wind may cost extra.
On Sun, 16 Apr 2006 14:21:07 -0400, "Walter Cohen"
If you build a cupola, it will exhaust all the air you
can get into the attic. It will also let more light in,
give you a place to hide antennae, gauss-guns, or snipers,
and give you easy access to the roof when you have to
re-shingle the whole thing because someone put black
shingles on an unventilated deck.
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