Design & DIY

Cottage Q&A: Pros and cons of running a furnace fan

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What are the pros and cons of running a furnace fan when away from the cottage? I am looking to save on hydro but I worry about moisture buildup.—Ruta Valaitis, via email

Well, there’s really just the one major pro and the one major con. And you already know what they are. “Air circulation is almost always a good idea, but a furnace fan can be expensive,” says Don Fugler, an Ottawa building scientist. “Depending on the fan motor and its setting, a circulation fan can use from 300 to 1,500 watts continuously.” (That said, it might be possible for you to make some adjustments to the unit, for example, replacing the fan motor with one that’s more efficient.) 

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But, “here is one interesting fact,” says Fugler. “If you heat your cottage with electricity during the winter to keep it above freezing, the furnace fan electricity use will not add greatly to that cost. Those 300 to 1,500 watts of fan electricity will simply offset 300 to 1,500 watts of electric heating.” (This is assuming that your furnace runs on electricity, not natural gas, oil, or propane.)

So, if you regularly visit your cottage in the winter, it might be beneficial to leave the heat on low when you’re away—Fugler suggests at least 5°C—along with running the fan. Bonus: this’ll probably make the cottage visit more pleasant, certainly when you first arrive. “If you let the cottage go down to -10°C, or whatever ambient temperature is in the vicinity, it will take all weekend for the surfaces and bedding to get up to comfortable temperatures,” says Fugler.

Have you had moisture problems before? “Existing conditions are the best indication of the need for more ventilation,” says Fugler. “When people ask if they should add more attic vents, I ask if they have had to replace roof boards or sheathing due to rot.”

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Air circulation will help to minimize localized moisture problems, says Fugler—for example, window condensation that drips down onto the windowsill. But no fan in the universe will prevent moisture buildup if water is getting into the cottage from, say, leaks or a high water table. You’d want to resolve those problems before trying any ventilation solutions.

This article was originally published in the Winter 2022 issue of Cottage Life.

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