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My attached 2 car garage typically gets over 100 degrees in the summer. I have an insulated garage door. The garage has a sheetrock ceiling and attic space above that is connected to the rest of the ranch home attic.

If I put a whole house attic fan in the garage, would it cool down most of the attic or only the attic near the garage? I was thinking I would get some benefit from cooling my attic down in the evenings after the sun went down?

  • Do you want to cool the garage or the attic ? My garage is insulated the same as the house and does gets no warmer than the outside temperature. Peak and eave vents usually make a fan unnecessary for an attic. – blacksmith37 Jun 30 at 16:53
  • My experience is contrary to @blacksmith37 's opinion that ridge and soffit ventilation is enough to keep attics cool, I go in a lot of attics and almost all of them are miserable in the summer. – batsplatsterson Jul 2 at 10:01
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To ventilate a garage you want to exhaust air from inside the garage to the outside of the structure and not into the attic. The garage gets so hot that I think you should keep the ventilation separate from the rest of the house. Also there may be code requirements to separate the garage from the living space due to fumes.

If I were going to ventilate a garage, I would put in an exhaust fan in the ceiling or in an outside wall and have a fresh air inlet vent as far away as possible, on an opposite wall if possible.

Another possibility would be to have a power exhaust fan like a kitchen hood going out the roof and a vent coming in a wall or through a soffit to keep the inlet air as cool as possible. I wonder if the largest ceiling exhaust fan of the type designed for a bathroom could be vented out a soffit to avoid a roof penetration.

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It sounds like you're getting some heat radiated from the attic down into the garage. Insulate the garage ceiling to cut this radiant heat. Do you also have direct sun on a garage wall? Can you shade and/or insulate that garage wall?

If you put a ventilation fan in the garage, it should vent to the outside, not into the attic, to keep car exhaust fumes out of the house. You would also need to look at an intake vent from the outside into the garage so the fan doesn't pull the a/c from the house.

How would you activate the garage vent fan? A manual switch could work but you may forget to turn it off at night. Consider a thermostatic switch, like those used on attic (not normally on whole house) fans.

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