I’m not a big fan of whole house humidifiers.

I have one, myself, in my own home, but it has been turned off for years and I haven’t really noticed the difference. Most humidifiers are sold as a way to make a home more comfortable. True, they can reduce the static electrical shocks one experiences in a (very) dry home. The additional moisture in the air also contains a lot of heat (after all, how did it become suspended in the air?), and that makes the home feel cozier – just as a wet sauna take cozy to the extreme.

But, generally speaking, humidifiers may do more harm than good, especially in homes that are tight — and increasingly more and more homes are being tightened or are being built tight.

When the temperatures in this St. Louis area recently got down in the teens and single digits, I was barraged with calls about window condensation and about water droplets on the ceilings of closets or near an outside wall. Think about it: any time your raise the relative humidity you also raise the dew point. After a certain point it doesn’t take much of a lower temperature to facilitate condensation. Windows, being windows, have limits in their insulating value. If the temperature outside is in the teens or single digits, do you really expect your window panes to stay room temperature? Double-paned windows are a great improvement, but they can only do so much. Likewise, closet doors are often closed and don’t benefit as much from the conditioned air of the home: so they’re colder. Attics and roof structures in most homes were not built with insulating the perimeter in mind, and so the ceilings near the outside walls are usually colder, too.

In fact an argument could be made that the lower the outside temperatures (and therefore the lower the humidity out there), that’s all the more reason to turn off the humidifier. In fact, if you look at most humidifier controls, you set them by the outside temperature and they throttle back the humidity to next to nothing the lower the outside temperature. So what’s the point?

You’re only asking for trouble, because if water is condensing where you can see it, what about where you can’t? Inside your walls maybe? Somewhere underneath that nice blanket of insulation in your attic? And, most horribly, even behind picture frames and mirrors.

And so I get a call, show up at the home and make a beeline to the furnace. What do you think I find? Of course: a humidifier. Invariably.

As I wrote above, this is especially troublesome in tight homes. In a tight home, often the humidity that is generated by the people living in it (respiration), by cooking, washing, and bathing, generates more than enough humidity. In fact, in those homes moisture often still needs to be removed.

So what can you do? If you don’t know how tight your home is, get it tested. It’s that simple. If you’re wedded to your humidifier and you see moisture, then turn it off (or at least way down), especially when the temperatures outside drop. Even then, though, you have to live with the knowledge that you may not know about the condensation you can’t see.

Me? I just turned it off. And, like I wrote, haven’t noticed a difference.

This entry was posted on Friday, February 5th, 2010 at 1:15 pm and is filed under Building Science, For Homeowners. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.