more roof ventilation is usually better.

Space attic vents evenly and mark the locations by driving nails up through the shingles (Photo 1).

Mark the roof venting locations from the attic, where you can see the rafters and avoid placing roofing vents over them.

Place all the roof vents on the same side of the roof. If your roof peak runs parallel to the street, put them on the backside, where they’ll be less prominent.

Grab a flashlight and inspect your attic during the winter. If you see dampness or frost, you need better roof ventilation and some attic vents.

1000 soft house less than R40 no air sealing needs 7 sq feet of vent 3-1/2 on the roof that’s 504 sq in that’s 10 of those square flat vents or 260 inches of ridge vent. Show less Read more 1 year ago (edited) 2

It is near impossible to get the attic and roof sheathing temperature the same as the ambient outdoor air temperature, due to the radiant heat from the sun. You would need three or four 1500 cfm power ventilators to come close to achieving that goal, at that point you'd be using enough electricity to run a central a.c. unit. Proper depth and type of insulation will do more than any amount of ventilation.

Wide rafters are 24" inch centers, narrow are 16" centers. He used narrower size (used in 16 centers) instead of wider size (not shown) baffles (for 24s). Unfortunately, as is, any blown-in insulation can now go down on either side of the narrower baffle and block the soffit slits necessary for air entry. Should have bought the wider size baffle that fits rafter-to-rafter, preventing any blown-in insulation from clogging the soffit entry slits. Costs a few cents more...

Attic fans work great and sure DO reduce electric bills

A powered exhaust fan will not work without proper soffit venting

As others have said, I think this works better with one fan as an intake, and another an an exhaust to keep the pressure balanced.

Bummer, incorrect and completely inaccurate information regarding attic fans. At least in a dry and hot climate. The more attic ventilation the better. It will extent the life of your roof and WILL decrease your attic temperature.

Any mod or installation if treated as an individual component is a scam. Contrary, a properly balanced and engineered system is beneficial. Attic fans do work, as long as they're incorporated into the ventilation ... as a system.

For me the attic ventilation temp difference of 145 to 110 is significant. I don’t know if you think that is significant but for us it certainly makes a difference in comfort for us. PS Over the thirty years in our home I have replaced the attic fan motor twice. The total cost of those motors was less than 100 dollars over those 30 years. During one season when we didn’t have the ventilation fan running we had a roughly $45-$50 per month increase in our electric bill. (The bill went from $190 to approximately $240 per month). From an energy perspective I guess that is not a lot of money but from a comfort perspective and level of A/C required it seems like a good return in the long run.

I don’t think that I can agree with you about the benefits of a powered attic fan. I live in Springfield, Virginia and I have actually measured a 30-35 degree difference in the attic temperature when that powered ventilator is running as opposed to when it is not running. I have had a comprehensive energy analysis done on my home and I know for a fact that my attic ventilation is not sucking air from our second floor into the attic.

there is a reason us HVAC people if we run into a house that has no ventilation in the attic and equipment is there, we will pull a salvage furnace blower and put it on a gable vent and turn it on for 5 minutes before staying up there for longer periods.