Yeah, it's been a super hot summer, and no relief in sight.

I think I might try one of those gable fans. Thanks.

Gary said,
There are a bunch of refs out there saying that AC powered attic vents don't payoff.

I think of my AC powered attic fan kinda like a very low cost heat pump.
It started up around noon today, but we never turned on the AC until about 3 PM.
By 6:30 PM it was cool enough to shut off the Sanyos again.
Without the attic fan, the house heats up earlier and stays hotter longer.

When we did turn the Sanyos on this afternoon, the house cooled down a couple of degrees, very quickly..

Right now, 7:45 PM, the ceilings are at 76.6F and the attic sensor is at 93.1F.

It's 76 indoors and 71.6 outdoors (and dropping fast).. :)



In my case, I don't mind paying a few extra bucks for power,
when it allows us to enjoy more hours of mild summer weather.
Not really expecting the fan to pay for itself in 10 years.. :p

It's going to be too hot to work up there..
Get some work lights and wait until about 1AM to go up there..
Or, take some big fans up there to keep a little cool when installing it..

Hi X,
Sounds like the way you manage the time that its on makes it work well for you.

I think there are a lot of variables -- how well the living space ceiling is sealed against airflow up into the attic, whether there is also a radiant barrier, how much power the fan uses, whether its a not so expensive DIY install or a more expensive install, ... I should not have made a blanket statement.

I got one of the solar powered attic vent fans when they were closing them out at Costco for $80. Its now installed near the outlet of my solar air heating collector in the shop to keep the hot air from stagnating up at the ceiling in the winter. It does a really nice job of keeping the air mixed up -- no controls needed it just runs automatically when its sunny :)

Gary

Whirlybirds
 

These Whirlybird type vents work fantastic and they take no power. My ac would lose ground when it was 95 plus outside. This year I installed 4 of these on my roof. The ac not only keeps the temp now, but actually cycles on and off rather than running continuously late in the afternoon.

I've seen a few of those around and wondered how they spin, is it wind or the hot air updraft?

Some people don't like them..
Attic Ventillation. Roof vents vs Whirly birds.

Actually both ways work , it's amazing how many cfm's they can pump out even with no wind.

If the wind turns them and the wind pressure on one side doesn't interfere
with drafting air up and out, that's cool..
But, around here there isn't a lot of wind on many of the hotter days..
Average wind speed here over the last 7 days is 0.5 mph
WOBURN WEATHER CENTER - Weekly Conditions
During the day, it's about 2 MPH sometimes.. In the winter, we get a lot more wind..
And that's when I don't mind some hot air in the attic.

However, if it's turning when the wind isn't blowing..?. That means the hot air
that's drafting up out of the attic is doing work.
Which means the air flow is being restricted, slowed down.

IMHO, a long ridge vent on the apex has got to be the best way to vent.
But it needs some air input in the soffit area to work best.
http://www.cornerhardware.com/howto/images/ht076_2.jpg
Sadly, my house didn't get any over-hang/soffit area.

My ridge vent spacer material is a plastic mesh cloth (like a pot scrubber).
I'm pretty sure it's the worse type to use, if you want good air flow.

The roofers has installed a real nice open-air-flow vent,
http://www.americanprideroofing.com/...ridge-vent.jpg
but they didn't have the proper size cap shingles to cover it.. Had to replace it with mesh junk.. :(

Don’t Waste Money on Powered Attic Fans
Barry Westbrook, P.E.

Most of us were taught from an early age that we can reduce our summer time cooling costs and extend the life of our asphalt shingles by sucking the hot air out of the attic. This is a wasteful, damaging, and dangerous myth that needs to be debunked.
Ironically, powered attic fans will almost always increase the cost of cooling the home. In many cases, they will also elevate radon gas levels in the living spaces of the home and create moisture management problems during hot weather. Finally, powered attic fans will not extend the life of the shingles. Why is this true?
Building scientists at Oak Ridge research facilities have conclusively proven that the amount of ventilation in attics does not significantly affect the cooling requirements of the building nor does it affect the life of the asphalt shingles. These findings are in direct contradiction of the long-held beliefs about the need for attic ventilation.
It turns out that actively ventilating the attic has almost no effect on the surface temperature of the asphalt shingle. Also, most of the heat transmission from the roof is radiant energy coming directly from the roof decking to the ceiling of the home. Although the air in the attic also gets hot, the air is not heating the ceiling. The ceiling is heating the air. Ironically, in most homes, powered attic fans literally suck the conditioned air out of the living space and increase the cost of cooling.
Considering these facts, is there a need for attic ventilation at all? For most attics, the answer is yes. During the winter months, the roof surface becomes cold. Without some ventilation, moist air from the living spaces will leak into the attic and form condensation on the roof decking whenever the temperature drops below the dew point of the air. Condensation on the roof decking can promote mold growth and wood rot. However, only passive venting is needed to prevent wintertime condensation in the attic. Powered attic fans are almost always installed due to concerns about hot weather.
Some attics need no ventilation at all. Many new homes and some existing homes are retrofitted with what is termed as a "closed attic assembly". In a closed attic, spray foam insulation is installed directly to the underside of the roof decking creating an “igloo” effect. This insulation thermally isolates the roof assembly from the attic. This prevents the radiant heating of the house in the summer time and prevents moisture condensation on the roof decking in the winter.

Closed Attic Assembly with Spray Foam Insulation

In summary, although there is a need for ventilation in most attics, the installation of powered attic fans are counterproductive. Homeowners looking to reduce summertime energy costs should invest in additional insulation or install radiant barriers instead.


Questions and comments can be submitted to the following address:
Barry Westbrook
℅ DocAir
4014 Flagstone Ct
Franklin, Tn 37069
615-373-2498

What if the ducts and/or air handler are located in the attic space?