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Using a heater to raise the bathroom air temperature: a moisture question

In my home I use a small, electric kickspace heater to raise the temperature in the bathroom during showering. The elevated air temperature allows for the air to hold more of the moisture and raises the window glass temperature, reducing condensation on that glass.

I am assuming that this elevated air temp gives the exhaust fan and the HRV exhaust more time to exchange that air and the moisture it holds. My question is this: by increasing the ∆T am I really just increasing vapor drive through poorly-sealed areas? The house was built 15 years ago and probably is not as well sealed at the window perimeter as I'd like. This is a timber-framed house with a SIPs enclosure.

Asked by Todd Stanley
Posted Dec 31, 2012 10:22 AM ET
Edited Jan 1, 2013 5:54 AM ET


2 Answers

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I seriously doubt that this is an issue. If you have an exhaust fan and/or HRV pulling air out of the room at an adequate rate, and run it for long enough, you're totally covered. Example, an exhaust rate of 40 CFM will change the air in a typical 5x8 bathroom with 8' ceiling in 8 minutes. That's a bare minimum scenario, you may well have more ventilation than that. Use a thermo-hygrometer and see how quickly the RH returns to normal in the room after use, Raising the air temp a few degrees only raises the moisture storage capacity of the air a small amount.

Answered by David Meiland
Posted Dec 31, 2012 10:30 AM ET


Vapor diffusion loading of the susceptible wood is all about the averages, not the extreme moisture events. Unless you're running the shower for hours per day, the 10-15 minute peaks aren't going to add up to enough to matter.

Answered by Dana Dorsett
Posted Dec 31, 2012 12:56 PM ET

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