Powered Attic vent fan

[roger61611]

Maybe start at 100, it will take some experimentation.

[TURTLE]

This is Turtle.

First read the instruction that comes with it and it covers this.

Second i like 105ºF and cut out and the lowest cut in point you can get to the

105ºF. Now most of the time the high point will be 125ºF and cut out at 105ºF.

TURTLE

[dk]

I just installed an attic vent fan on my roof. What should I set the temperature to??

TIA

[John Willis]

On Wed, 13 Apr 2005 21:33:55 -0400, dk scribbled this interesting note:

Depends on your climate. 'Round here in North Texas I set them at least to 110 degrees. Set them much lower than that and they'll run half the night trying to cool the attic since we see some nights here that don't cool off to less than 90 degrees until after midnight!

-- John Willis (Remove the Primes before e-mailing me)

[Buck Turgidson]

Mine is set to 100, and it comes on early afternoon and runs until about

9pm during the summer here in the Mid-Atlantic.

[stretch]

dk I recommend setting it as high as possible. This is because the fan will put your attic into a negative pressure. If you have air conditioning, any openings between house and attic like for ceiling lights, ceiling fans, around tub showers, etc, fan will suck ac out of the house. Any time you suck air out of the house, air will suck back in somewhere else. This makes your attic cooler but actually increases your cooling bill for the house. If you are doing work in the attic, turn the fan thermostat down, otherwise turn it as high as possible. Being an AC contractor, and having test equipment to measure this, you couldn't GIVE me an attic exhause han. It acn also cause gas furnace and water heater flues to back draft! Carbon Monoxide! Yuck! Depends on your house, how tight is construction, how many openings between house and attic, how many soffit vents, how big is fan etc.

One idea is to install 2 fans, one blowing air in and one blowing air out. Attic pressure stays more neutral, less side effects. Then you can turn the thermostats down without hurting things much.

Stretch

[JimL]

How long do you want the fan to run? 24 hrs/day? 6 hrs?

It takes some effort experimenting, but here in the south, I want my electric fan running no longer than until about an hour after sundown during the summer months. That ends up being about 105 to 110 before it comes on at about noon.