Recommended attic fan thermostat temperature settings


I’m trying to write up one of my 4 required mock-up inspection reports for membership on this organization. I inspected a house recently that had the attic fan temperature settings at 115 degrees and 120 degrees (one at each end of the house). I’ve seen recommended settings to be any where from 95 degrees to 105 degrees. Does anyone have any details that they can share with me on what these settings should be from an inspectors point of view?

Please advise,


This article may help you a little here;

How much attic ventilation is required to provide proper temperature and moisture control? A number of studies sponsored by federal energy funds are under way to look at ventilation rates and methods.
However, several studies previously made can help with this decision.

The maximum ventilation rate is required to remove heat during the summer cooling months.

Attics can reach temperatures of 150 to 160 degrees F during a summer day, although outside air temperatures are only 95 to 97 degrees F.
The cooling load for a home air conditioner depends on the difference in temperature between the inside and outside air, and reduction of attic temperatures from 155 degrees to 105 degrees F will result in a significant reduction in cooling load. In a home with poor ceiling insulation, heat movement through ceilings may account for 30 percent or more of the total cooling cost.

With a well-insulated ceiling, this source of heat may account for only 12 to 15 percent of the total cooling cost.

Thus, high attic ventilation rates are most important for poorly insulated ceilings. A poorly insulated ceiling is one whose R rating is less than 14 or one with fewer than 4 inches of fiberglass, rockwool or cellulose insulation. :):smiley:

Where do you live?


Did you get my IM?

Please advise,


this really has a lot to do with the area You live in imo…jim

In the South, if you set them for 95, they’ll be running 24/7 all summer long. I think 115 to 125 or so would be appropriate.

Thanks for all of the feedback. Since I live in the northeast, I thought about recommending 105 to 110. I’ve found some articles that suggested temps as low as 90.



Now forget about the numbers on the attic fan thermostat - they are horrendously inaccurate. Set it so that it comes on when the attic reaches the actual target temperature by using a thermometer to verify real temp.

Steve, sorry I lost track of this thread.

As others have said, you should set the thermostat at what the average nighttime temperature (in your attic) is for your area.

There is not going to be a big variation here, but you don’t want to set a southern house too low or it will never shut off (wasting energy).

In New England I used to set mine at 80. There was no trouble reaching that temperature at sundown where I lived.

Solar loading of the roof system brings temperatures in the attic extremely high, even in cool climates. These temperature settings are not really critical. The difference in setting the thermostat at 90 versus 100 is only a matter of minutes in some roof exposures. If the thermostat is set a little bit high, the natural convection cooling of the attic ventilation system will bring the temperature down the rest of the way in a reasonably short period of time after the fan shuts off.

Wow. Thanks for all the great inputs.



Very informative thread.

Nice information. I was having this kind of problem a long before. I was all confused between the attic ventilation temperature and could’t get the proper answer anywhere. I finally decided to go online and ask my query, Go here. Got the proper answer then.