My parents had one of those in the 1950's before they had AC.
In hot, humid weather the who house fan basically blows the hot air
I think the goal is to blow the hot air out of the attic so it doesn't
migrate into the house.
As hot air rises *and* the hottest air is in the attic, how do you
propose it "migrate" to lower parts of the house?
My understanding (and what I did via an attic roof fan) is to cool the
attic air so that living spaces adjacent to it are not next to as-hot
attic air and thus reduce the AC demand in those living areas.
If there's one or more active fans on the attic vents (as I indicated
and previous responder suggested) then the hot attic air would escape
(i.e. be blown out) as cooler air, pulled into the attic via a fan
entered. Thus lowering the attic air temperature. Thus lowering adjacent
living space heat. Thus lowering AC demand. Thus lowering AC costs.
Typically, these are thermostatically controlled so that once they reach
some "reasonable" temperature level, you don't continue to blow living
space air into them.
Attic/gable fans can make a big difference in the Arizona desert,
lowering the attic temperature form 150+F to closer to the ambient 115F
My unvented cardboard box solar cooker can reach close to 300F in the
summer months. Was telling a former AZ resident about the solar cooker
and he wondered why I bothered as I could probably accomplish the same
thing by placing the cooking vessel in the trunk of the car...
For energy efficiency I would recommend more insulation above the
Roof venting will lower the temperature in the attic crawl space but the
main advantage of proper roof venting is that it extends the life of the
roof. If you do vent the roof at the ridge you should also add soffit
venting at least equal in area to that of the ridge vent for proper air
Almost totally non-applicable to the OP:
* "Water vapor will condense..." Not in 0% relative humidity
* "Frost will form....." In Tuscon?
* "... problem of mildew..." Meh.
* "Ice dams..." Again, in Tuscon?
Commercial brochure on ridge vents. Good explanation (except for the bit
about exhausting hot, HUMID, air).
Typical government simplistic check-list. Superficial, but good,
Heh, heh. Absolutely right, HeyBub. Mr Barss, There are some folks
here with excellent ideas. Namely: Make sure you've got soffit vents
if you're installing ridge vent. Make sure your insulation doesn't
cover the soffit vents. If it's worth doing, overdo it (insulation-
wise). I'm not sure about those radiant barriers, as the underside of
the decking _must_ breathe very well. I roofed for twenty-plus years
in MI, and I'm looking at re-doing my roof here in Tucson pretty soon.
I'm probably going with painted standing seam metal. I wish copper was
more affordable, or I was richer... Tom
On Wed, 17 Jun 2009 18:06:57 +0000 (UTC), Andrew Barss
How thick is the insulation now? Blown insulation will settle over
time and perhaps not have the same R value.
In a pinch, staple cardboard from the vent and above the blown in
Spend a little time and find out why your doors and windows, leak most
energy. Smoke pencil, exotic incense helps show a draft.
DIY home audit
Soffit vents are 'required'.
Use the rigid foam panels that keep a clear air path over the insulation
where it meets your walls.
Also, if you use a swamp cooler, install a vented access door somewhere in
your living space that vents into the attic. When the cooler is on, the air
flows up into the attic (no need for an open window). With the cooler off,
the vent flaps close and block attic air from returning into the house.
A 'whole house fan' installed in the same way can be used to flush cool air
into the attic in the early morning and flush hot air out in the evening.
I can't find a manufacturers name on mine, but its aluminum and has felt
seals at the edges of the slats. Sealing has never been a problem (no bugs or
other things get back through), but during the winter when I'm not running
the cooler, I place a plastic cover over the vent to stop all air movement.
Here is a link to a similar vent:
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