The dry season

Once temperatures fall and the heat comes on, the battle over humidity commences. On one side is too little humidity: Desert-dry air with nosebleeds, itchy skin, sparking static electricity and separating wood floorboards. On the other side, too much moisture: Lots of humidity makes a body feel good, but it causes damaging window condensation, moldy walls and attics, and a dust mite population boom.

Getting it right depends on where the battle is waged.

In older homes, air tends to be dry. That's because outdoor winter air is dry; the colder it is, the drier it is. Entering easily through cracks, gaps and spaces around windows, doors, foundations, it dries household air. It also needs to be heated by the furnace or boiler, which makes the air even drier. The leakier the house, the drier the air.

Solution: Buy a humidifier (and stop those leaks).

Newer homes tend to leak less. Built tighter with better insulation, they're less drafty, need less heating and so are less dry.

Indeed, many people can live comfortably because household-generated moisture (baths, cooking, etc ) offsets the amount of outdoor air that comes in needing to be heated.

Solution: Don't bother with a humidifier.

Too bad we can't just stop there. But it's not that simple.

Homes don't act their age

Some older homes have enough moisture, just like newer homes. They've been improved with new windows, doors and siding, and weatherized with more insulation and weatherstripping to fill gaps, holes and cracks. They aren't so leaky anymore. Adding humidity can only cause problems.

On the other hand, most new homes are so well built and the flow of fresh outdoor air coming in so low that indoor air quality suffers. Air is too moist, mold and bacteria flourish, dust mites proliferate, all of which taints the air. In addition, traditional fuel-burning appliances -- furnace, water heater, boiler, fireplace -- can malfunction due to lack of air, adding more contaminants. That's why, since 2000, Minnesota Building Code has required mechanical ventilation of homes. It makes sure there's enough air in homes for occupants and appliances by turning air over several times a day. Trouble is, sometimes these new homes act like old homes -- they're too dry.

So what's a homeowner to do?

Invest in intelligence: Buy a hygrometer. This device, available at hardware and home stores, measures the humidity in your house. It can tell you how to wage the humidity battle, so to speak.

You have to strike a peaceful balance between what feels good (40 to 60 percent relative humidity) and what is best for the house (20 to 40 percent). You want to add enough moisture for some comfort without causing excessive condensation on windows, in the attic and wall interiors. Monitoring window condensation is a quick check.

If you decide to buy a humidifier (see accompanying guide), you must monitor it. The last thing you want to do is buy a humidifier and then just let it run. Indoor humidity levels are linked to outdoor temperature. The colder it is outdoors, the lower humidity must be indoors to protect the home's structure. (See accompanying chart.)

Remember, when it comes to the moisture tug-of-war, battles can be won, but the war never ends.

Karen Youso • 612-673-4407