It’s that time of year when heating systems start coming out of their summer hibernation. (Except maybe in Vermont. Michael Blasnik’s Nest data showed that Vermonters are about the last to start heating their homes in the fall.) Then everyone starts looking for their lotion and lip balm. Gaps appear in hardwood flooring as it dries out. Buildings begin to creak and pop. And then the humidifiers come out.
Yes, humidifiers can help with low indoor humidity. But what effect might they have on indoor air quality?
Why does indoor air get so dry in winter?
We’ve been through this before. I wrote about it in A Humidifier Is a Bandaid back in 2013. Shortly afterward, a certain manufacturer of humidifiers called and left me a nasty voicemail. I didn’t save it, but the gist was, “You don’t know what the hell you’re talking about. Call me back so I can yell at you.” I didn’t call back.
OK, let’s go through it quickly.
I proved this with the psychrometric chart in the bandaid article. There’s no disputing it.
How does that cold, dry air get into a home? For most homes, it comes in through infiltration. Most homes leak. A lot. When they leak, heated air with decent humidity leaves the building. Cold, dry air enters. The humidity goes down. The lotion comes out. The humidifier gets turned on. A better solution is to reduce the infiltration with air sealing.
The ideal range for relative humidity
This is the part that confuses a lot of people. If you go online, you can find all kinds of recommendations for what the relative humidity should be inside a home. Some say 30-50% RH. Others, including the creators of the chart shown in Image…