Mike Green’s Ontario home is well built, and his low energy bills convince him that the house also has been well air sealed. But there is a problem he’d like to solve: low indoor humidity during the winter — low enough to cause floors to crack.
The 6,000-square-foot house is heated with a forced-air system and is equipped with a heat-recovery ventilator. Green has set the HRV to run only when indoor humidity exceeds 50%.
“In the winter the humidity in the house is around 25-30%,” he writes in a Q&A post. “We are noticing that the floors are cracking a bit at this lower humidity. Why would the humidity be so low in the house?”
Green asks whether running the HRV around the clock would help, or whether he should buy a small humidifier to put more moisture into the air. Ideally, he’d like to see indoor relative humidity at about 40%.
What’s the best way of accomplishing that? That’s the topic for this Q&A Spotlight.
Make sure the HVAC system is balanced
Outdoor air is typically dry during the winter because cold air is capable of holding less moisture than warm air. Even so, says Dana Dorsett, the air inside an occupied house in winter should have a relative humidity of at least 30%. That, he says, is at the low range of what people would find comfortable (50% is at the upper end of this range).
He suggests that a forced-air heating system that is not perfectly balanced, or one that has a makeup air port (an outdoor air duct) connected to the return-air plenum, will increase air infiltration and lower the indoor relative humidity.
The Energy Star program requires that ducted heating and cooling systems be designed and installed to ensure that…
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