View Single Post
Old 06-21-2020, 02:39 PM   #1 (permalink)
Master EcoModder
Ecky's Avatar
Join Date: Dec 2011
Location: New Zealand
Posts: 5,030

ND Miata - '15 Mazda MX-5 Special Package
90 day: 39.03 mpg (US)
Thanks: 2,883
Thanked 2,527 Times in 1,562 Posts
What's the verdict on attic fans?

When I purchased my home, the inspector commented that the attic ventilation was inadequate.

Using some online calculators suggests that my soffit (intake) venting is large enough, but the home does not have a ridge vent and the gable vents add up to only 20% of what is recommended for a home which may not have a proper vapor barrier in the ceiling. I'm scratching my head on just how to get 560 square inches of Net Free Area with just gable vents, which are typically around ~60 square inches of Net Free.

So my question is, what about attic ventilation fans, on a thermostat / humidistat?

There seem to be plenty of builders and DIYers still recommending these, and plenty more that suggest to proceed with caution. Alarming to me is that Georgia has banned attic fans state-wide, and logic of this is that fans create negative pressure in the attic, and the make-up air is pulled from conditioned space in the home, often causing more harm than good.

My home seems to be relatively air-tight, and there's a minimum of 12-14 inches of blown in cellulose insulating the ceilings. My issue instead is the accumulation of hot air in summer and moisture in winter. I'm not so much concerned with reducing air conditioning load (there's relatively little) but rather, to improve the longevity of my roof.

What's the verdict?

  Reply With Quote