Home was built in 1960, located in New Hampshire. One story house with
a gable roof/Hip.
In the summer the temperature difference between the living area and
attic was in the region of 25F-30F, and upto 35F-40F on the hottest days.
Went up in the attic and found that the ridge vents were OK but soffit
eaves were blocked by the second layer insulation. So I pulled back the
insulation from the edges and inserted "prop-a-vents" along the sides.
About 2/3 of the work was done while it was still hot and I noticed that
there was a small temperature-difference drop on most days but on hot
days the differential was still 30F or so.
Now I've just finished the rest of the work, but it's not hot enough to
compare the temperature difference -- it's about 17F today on a cool
day. However, it is easier to get contractors to come out and do work
in the attic or on the roof during the cool season :) So I'm wondering,
1. Have a roof vent installed - it's just a small, molded, vented
plastic square that goes on the roof and vents air to help the ridge
vents, and will that help on hot days, or
2. Have a power vent installed? The fan itself is not too expensive,
but it would require running a new power circuit to be run up from the
basement to the attic, which will raise the total cost quite a bit.
I had a thermostat powered fan in my attic. It would come on low speed about
10am, high speed about noon, and run until about 10pm or so. It made no
difference in my power bill, it just made me feel better thinking my attic
was not as hot as it would be without it. If I had to do it over again, I'd
just have a couple of good vents and leave it alone.
I'm running a power vent as a band aid until I can get around to
properly venting the soffits, I have a ridge vent 3 gable vents and it
still runs often till the wee hours of the morning. I'm on my second
motor, (I've got to get motivated to finish the venting). i was able to
tap an existing line in the attic and split off a wire for it, as a
bonus I now have lighting when I change the motor.
A 30 degree diff between the living area and the attic on a hot day is
excellent. It's not unusual for attics to reach 110+ on a hot day,
even with excellent venting. That's well within the capability of the
insulation to handle. Would you be concerned if during the winter the
outside temp was 30 deg below the inside temp? Attic ventilation is
important to keep humidity down and to prevent really high temps, like
140, which are possible with poor ventilation.
So, I wouldn't do a thing. Plus, installing a powered fan raises the
possibility of a considerable amount of air just being pulled in via
the ridge vent and blown out by the fan, effectively short circuiting
what is already there. Also not clear that adding a few more box vents
is going to do much either.
I think the latter is the key point -- a powered fan may not be be much help
because of cross currents with the ridge vents. Many years ago I installed
a powered vent at my house in Ohio and immediately noticed a significant
decrease in my need for air conditioning. For that house, the powered vent
was worth it.
Since then, insulation has gotten much thicker and electricity more
expensive. Reportedly, tests now show that a powered vent will use about as
much electricity as it will save in a/c costs and that the cost-effective
way (for houses with soffit and ridge vents) is to add more insulation.
Nevertheless, I did put in a powered vent (I have soffit vents but no ridge
vents here in hurricane country). I can't quantify a savings in my electric
bill, but now if I have to get something from the attic the temperatures are
bearable, even here in Central Florida. Regards --
Thank you Ook, Eric, trader4 & Jim R for the replies. Looks like most
of the replies aren't favorable towards the powered vent, so I'll
probably stay away from that.
One thing I forgot to mention is that there's no air-conditioning in the
house, so the attic staying hot is a major discomfort to the wife &
infant in the living area, which is why I am trying to address the
problem. I did install a window unit, but in some areas of the house
where there are larger, connected, open spaces, I am not sure what to
do. I'm considering a split-type a/c in the future.
Anyway, back to the attic ventilation:
Would any of you recommend installing a whole-house fan? Keep in mind
that I'm in New Hampshire and July & August are probably the months that
get really hot.
And if yes to the whole house fan, is a powered vent required on the
roof? I was under the impression that eaves+ridge vent would be enough.
Again, the fan itself is not too expensive, but the installation & labor
makes me think twice. As an example, the fans can be $200-$400, but
the installation estimates are between $1000 (without powered vent for
the roof) & $1800 (with powered vent).
We have a whole fan here in San Jose and works well without AC. For this to
work well, the outside temperature in the evening time must be comfortable,
or it is no use to turn on the fan. The idea is to pull in cooler air than
inside the house and vent the hot air in the attic. Pulling in hot air into
the house is not what you want.
I picked up what was probably sold as a gable vent fan for a few $ at a thrift
shop. I slipped foam pipe insulation over the 4 mounting bars that came off
the fan. This I then set over the attic access hole in my house, blowing up
into the attic. I plugged it in through an X10 appliance module, which allows
me to turn it on/off remotely. When I want to cool an area, I turn on the fan
and open a window in the area to be cooled. Or, I open a window
downstairs so that air will be drawn through the whole house. This thing
makes a big difference in the comfort of my home (in Seattle).
I'm sure that part of its effect is due to the air it blows up into the
attic, cooling the attic at the same time it vents the house.
It's not a real "whole house fan", but is an effective substitute. I don't
really need anything more.
In my first house (located in Ohio) I installed a squirrel cage out of
a furnace in the finished attic vented through the gable. I plugged it
into the over head light and when we wanted to cool the house I just
opened the attic door and turned on the light switch. It was so
powerful if you didn't block the door open it would suck it shut. We
never had A/C and never missed it, the constant flow of air made it
It sounds like you have done all you should do and your venting system
is working well. I doubt if adding power venting would help anything other
than the bottom line of the vent manufacturer and the electric company.
A whole house fan would probably be very useful in your area, where
there are many times the temp drops down nicely overnight. This would
quickly cool the house down close to outside temps and it could stay
reasonably cool till at least mid day.
All that is needed is enough exit area for the fan rating. That is
specd by the manufacurer.
Sounds high to me. The whole house fan is more involved, because it
involves cutting/framing an opening in the ceiling. But $800 for a
powered attic fan is way high, unless the install is complicated for
some reason. You can get a fan for $100 that will install either in
a gable or in a new hole cut in the roof. I'd say it should cost more
like $400 installed.
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