I am in the process (day1 of 2) of getting a new roof. I have a whole house fan - Louvered ceiling type. House was built in 1968 so I have no spec on that fan. It has (or had after they ripped it out) a roof ventilator with fan. The roofers removed the “mushroom” bowl shaped thing on roof and disconnected the fan from electricity.
They are telling me I don’t need it anymore because they are putting on a ridge vent. Currently I had this ventilator and 5 turtle type vents.

Are they correct not to put the mushroom ventilator back and hook it back up?

Please help.

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    Wow I would tell them they are responsible for putting it back in! A powered roof fan can drop your attic temperature 20-40 degrees in the summer and reduce the energy bills for AC and make the home much more livable! I live in western Oregon, not a hot place but roof fans are one of my first upgrades and have been for many homes. If flipping a home without ac in the summer installing a solar attic fan is something we have done on close to a dozen houses.
    – Ed Beal
    Commented Feb 3, 2021 at 2:21
  • Thank you Ed. I live in Midwest southern Indiana and we have about 2 months of 100+ degrees without end. Getting worse. Commented Feb 3, 2021 at 2:32
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    @SammaPlatte-read this article regarding powered attic fans [link] (energyvanguard.com/blog/38676/…)
    – ojait
    Commented Feb 3, 2021 at 3:28
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    @SammaPlatte- or choose any article from this Google search: [link] (google.com/…)
    – ojait
    Commented Feb 3, 2021 at 3:30

1 Answer 1


Powered attic exhaust fans sound like it would be an sure way to keep your attic from becoming an oven in the summer. But unless your attic is completely draft free and sealed from the living space below running an attic fan will increase your electric bill and increase the cooling load on your HVAC (cooling).

When the attic fan runs it is pulling air from the house while make-up air is being drawn in from the outside through any gaps (door thresholds, window frames, etc.) your conditioned cooled air is being pulled into the attic and exhausted out the vent.

A ridge vent when properly sized, allows an easy route for the hot attic air to escape;the vent is at the highest point in the attic.

The make-up air being drawn in is through the soffit vents (openings).

If the roofers have calculated how many roof vents you need accurately than there is no need for the energy consuming powered fan. A quick way of finding the number of attic vents is for every 300 square feet of attic floor space there should be 1 square foot of vent opening*.

*Audel HVAC Fundamentals, Volume 1.

  • Thank you so much for your reply. So is the whole house fan (it’s in the garage ceiling and I have crank louvered door from house to garage) not at issue? I think I understand that the ridge vent in the roof will be adequate. The ridge vent is replacing the 5 turtles and that powered fan. I just want to make sure that I can still run that whole house fan without issue. I run that thing a lot in spring and fall with windows open or screen doors. I’m just probably overthinking it. I just don’t want to hurt the house. Commented Feb 3, 2021 at 2:15
  • No the attic is not air tight. I have a ton of can lights Commented Feb 3, 2021 at 2:17
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    No an attic fan will not increase the load on the AC it will reduce it, attic fans draw cooler air from the soffits and exhaust closer to the peak reducing the attic temp and heat load on the ceiling, if the trunk lines are in the attic reducing the heat also helps there. The cost increase for most attic fans is under 5$ per year they save many times there cost to operate.
    – Ed Beal
    Commented Feb 3, 2021 at 2:25
  • I have 2019 sq ft and the length of the house is 69’ Commented Feb 3, 2021 at 2:26
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    @SammaPlatte- The roof sheathing (plywood) is typically cut away on each side at the roof's peak. Yes as you stated about 1 1/2-2 inches (on each side). The rafters are the only interruption to the ridge vent. Also (depending on the brand) the ridge vent starts and ends several feet after and before the gable (or existing) wall
    – ojait
    Commented Feb 3, 2021 at 4:06

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