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Dry Air, Winter Sniffles

Paul Kando

“The air is so dry in our bedroom, you can’t sleep right”, you complain. With two humidifiers running, it’s a little better, but the air still feels too dry. Your nose feels like you are having a permanent cold. This time of year this is a common complaint – and humidifiers are not the answer.

photo credit: Erie Times-News

As the air warms in a heated house, it absorbs more and more moisture. The warm, moist air expands, becomes lighter, and rises. If it has a path to escape from the upper part of the house – through cracks, around wires, electrical outlets, around the attic hatch – it will do so, taking with it all the moisture it has absorbed. The escaping warm air is simultaneously replaced by cold outdoor air infiltrating through small openings in the lower part of the house. Cold air, of course, holds less moisture, so the colder it is outdoors, the dryer the infiltrating air.

Now your furnace or boiler goes to work, heating the air. As it heats up, it absorbs whatever moisture it can find, including the moisture your humidifiers spew into the air. It is an endless cycle, as long as your heat is on. In short, an air-leaky house sheds airborne moisture and creates an endless supply of dry indoor air. No wonder you have the sniffles.

“Yes, but the humidifiers put a gallon of moisture into the air”, you protest, not to mention the showers you take, the water you boil on the stove, the watering of indoor plants. Why, the old widget in the exhaust duct of the clothes drier even directs the drier’s wet air into the house. How can all that moisture escape?

Several years ago German researchers explored exactly how much airborne moisture can escape through a small hole from a house. They allowed moist indoor air to escape through a one millimeter (about the size of a pencil-point) hole, then cooled the escaping air, causing the moisture to condense. Measuring the accumulated condensate after 24 hours, they have found that just under a pint of water had escaped through that small 1 mm hole.

I carefully measured the number of millimeters in the openings of a standard electrical outlet. They add up to 114 mm2, meaning that 114 pints – about 14 gallons – of airborne moisture can move through a single electrical outlet through a 24 hour period. That’s more moisture than there is available to each and every outlet in a typical house. In other words, a leaky house, through all its leaks, large and small, is capable of shedding all the moisture a household generates in it, including your two humidifiers.

So you suffer the sniffles. Meanwhile, as we discussed in earlier columns, all that escaping moisture can seriously damage your house. So adding more moisture is not your answer. It may even cause your house to get the sniffles too. Plug up those leaks instead, and provide the proper ventilation to manage the moisture retained inside.