Humidify at your own risk Energy Q & A

Q. In the Monday paper you had an article about attic moisture. Dr. Dick Hill indicated in the article that one should not use a humidifier under any circumstances. Was this just in reference to the attic moisture issue, or did he mean not ever? I was under the impression that it made the air feel warmer at a lower temperature. Thank you.

Lisa Colburn, Orono

Answer provided by Dr. Richard Hill, retired emeritus professor of engineering at the University of Maine.

A. Lisa Colburn asks if humidifiers are only relevant to moisture in the attic, or also to thermal comfort.

Check Google with the words: “Fanger’s comfort equations”; then click on the second item, “Prediction of thermal comfort.” Notice that the comfort level at a relative humidity of 20 percent can be achieved at a relative humidity of 40 percent with a 1 degree drop in air temperature.

Stated another way: If “Room A” is at 70 degrees and 20 percent relative humidity, and “Room B” is at 69 degrees and 40 percent relative humidity, the two rooms will be perceived as having the same comfort level.

Consistent with standard engineering assumptions, the air in a dwelling will “turn over” once every two hours. A typical home may have a volume of 13,000 cubic feet. To lift the relative humidity from 20 percent to 40 percent will require the addition of a bit less than one quart of water each hour.

The energy required to evaporate this water will, over the heating season, require about 50 gallons of heating oil. This quantity of oil cannot be saved by a 1 degree lower thermostat setting. But there is a bigger issue. When air at 70 degrees and 40 percent relative humidity leaks into sections of the building (the back of electric outlet, around plumbing vents, etc.) where the surface temperatures are 45 degrees, then the moisture in that air will condense. The wallpaper in the back of an upstairs closet will mold, paint on window sills will peel, etc. I have never seen a Maine residence that could tolerate such high humidities.

Don’t humidify. Little increase in comfort is achieved, great damage to the building is possible, and energy cost savings through thermostat set-back are nearly nonexistent.