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A smarter attic fan?

BryanPringle | Posted in Mechanicals on

In doing retrofit insulation projects, attic ventilation is a topic that frequently arises.  And here in coastal Maine, it can be touchy as well.  Best practice attic ventilation is soffit to ridge channels, which will allow free flow of air and great year round drying potential.  But many homes only have gable vents or less, and soffit to ridge venting may be impossible at worst or impractical at best. We have found that the attics without ventilation may be as dry as those with ventilation, and some with ventilation are quite damp, even after air sealing.

The bottom line: the humid air mass of a coastal New England summer puts a lot of stress on attics (and other enclosed spaces) as temperatures cool in the fall and that air mass can no longer hold as much moisture (and thus carry it away).  What can be done to improve a building’s chances against these conditions?  I’m thinking mechanical (attic) ventilation may help.

There are plenty of attic fans out there, and in general, they don’t do a lot to help with this.  But what would help is a fan with a control module which measures both attic conditions and outside conditions, and turns on only when there is drying potential by increasing the air exchange rate.

So therein lies the question: Does such a product exist? And do we think it would really help?

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  1. Jon_R | | #1

    > it would really help?

    Under some circumstances, I'm sure it would. Make it reversible and variable speed.

    Note that some people take data from "exhaust only attic ventilation at CFM sufficient to remove significant heat" and apply it to all forms of powered attic ventilation. This results in nonsense conclusions.

  2. charlie_sullivan | | #2

    See this previous discussion:

    There is such a product. I link to the discussion, not just to the product, to include Martin's comment about the need for good air tightness for it to be useful. I also note that I'm not sure you can get one in North America.

    1. BryanPringle | | #3

      Thanks Charlie, I did not see this thread when I searched earlier. Obviously we're putting a lot of effort into air sealing any attics we treat, but like Martin mentioned, the best efforts leave it less leaky, not air tight. That said, in the intersection of building durability/moisture management and energy efficiency, we take both whenever we can, but always show preferential treatment to building durability, which is why I'm looking for something like this.

      So the follow up to anyone else looking at the thread is: are you aware of a product like this (specifically the fan controller) available in North America?

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