As autumn temperatures drop, homeowners in cold climes adapt by installing storm windows, weather-stripping doors, and otherwise sealing their houses against the coming winter. But reducing drafts has an invisible risk. While it may lower utility bills, it can also trap pollutants such as mold spores, dust, and combustion fumes indoors.
Whether houses are closed up to retain heat or to conserve air-conditioning, the air inside can become many times more polluted than the air outdoors, according to the U.S. Environmental Protection Agency.
At its worst, indoor air pollution can cause severe illness, including respiratory diseases and neurological disorders. Even mild contamination can inflame allergies and asthma or just foul the air. To assess "sick" buildings, environmental consultants measure pollution levels, track sources, and prescribe solutions.
In general, though, a few basic household repairs and maintenance chores -- designed to limit sources of bad air and expel the problems that do arise -- will prevent the sort of extreme conditions that require professional intervention.
The most dangerous pollutant is also the easiest to avoid: exhaust, which leaks into the home from furnaces, water heaters, and wood-burning stoves. It contains a host of noxious substances, including carbon monoxide, which is odorless and deadly. To make sure exhaust exits through the chimney, schedule regular tune-ups for fuel-burning equipment -- yearly in the case of oil-fired devices. (Your fuel supplier may offer service or be able to recommend a company that does.)
In addition to ensuring that burners are operating efficiently, the technician should check for blocked or broken pipes and for clogged flues, which require cleaning by a chimney sweep. Exhaust can also find its way into the home from attached garages. Don't warm up the car in the garage or run other gasoline-powered equipment there. And, to be certain your family is safe, install a carbon-monoxide detector in a central hallway on each level of the house.
Far less dangerous, but more insidious, are dust and pet dander, pollutants scattered by your home's inhabitants. Frequent, thorough cleaning is your best defense, of course, but vacuuming can actually increase airborne pollution because particles that get sucked up can escape through pores in the dirt collection bag.
A new generation of vacuum cleaners solves this problem by using high-efficiency particulate air (HEPA) filters. Some even have antimicrobial chemicals in the filter to kill dust mites -- microscopic critters that feast on organic matter in dust and that can trigger allergies -- and other invisible organisms that they catch. Such supercleaners can be had for $300 to $600, which may be a worthwhile investment if your machine is getting old. Otherwise, you should vacuum with the windows open when possible and empty the canister after each use or change the bag before it gets full.
Dust tends to be most prevalent in bedrooms, so wash your sheets weekly using the hottest water recommended for the fabrics (preferably 130 degrees or more). Duvet covers, comforters, and shams should receive a monthly cleaning. Send bedroom throw rugs to the cleaners every other month, more frequently if you have pets. Since the mattress, box spring, and pillows are impossible to wash, try encasing them in hypoallergenic covers to keep out dust and mites.
Dust mites are not the only microscopic organisms that can affect indoor air quality. Mold and mildew grow on any surface that stays wet for at least 72 hours and contains organic compounds -- as do wood, paint, wallboard, and some types of insulation -- for the fungus to feed on. The same black splotches that sometimes appear around bathtubs can grow unseen inside walls and ceilings. Once it has found a home, mold spreads by releasing spores into the air. Mild mold infestations will inflame allergies; severe cases can force homeowners to abandon their residences.
Water stains on walls and ceilings are classic signs of damp, mold-friendly spots. Call a professional as soon as possible to eliminate the source -- whether it is a leaky roof, clogged gutter, or faulty plumbing -- and to remove soggy drywall or plaster. Still, not all dampness is caused by water in its liquid state. Excessive water vapor will condense on surfaces if left unchecked, and provide a home for mold virtually anywhere, including inside walls.
Localized humidity can largely be averted with ventilation: Always use bathroom fans during showers and for 20 minutes afterward. Kitchen stoves should have hood fans that vent to the outdoors (and should be used); those that recirculate air have no effect on humidity. Since dryers take water from clothing and turn it into water vapor, their vents must discharge outside and be kept free of clogged lint; an outdoor-venting fan over the washer also disperses moisture.
And still another vent, fitted with a fan that is installed in the roof, will pull hot, moist air out of the attic and draw in fresh, improving the atmosphere throughout the house. Attic fans should automatically operate when needed -- electric models do this when a thermostat in the attic reaches a preset temperature; roof-mounted solar-powered units activate when the sun is beating down.
Heating and cooling ducts make a perfect home for mold if they are dirty and damp, and because they circulate air, they will spread trouble by blowing spores throughout the house. Have ducts examined and cleaned yearly, and make sure cooling ducts are insulated where necessary to prevent condensation.
If you follow this maintenance routine and upgrade to a HEPA filter on the furnace or air conditioner, the network of ducts can become an efficient filtration system for all the air inside a home. HEPA filters are also made for free-standing appliances that can cleanse the air in a single room (the systems are available at home centers).
Because central air-conditioning dehumidifies the air, it makes the whole house less habitable for molds. Window air conditioners have the same effect in the rooms that they serve, but they are less effective as air purifiers. Still, you need to change the filter monthly, and it's a good idea to upgrade to a premium filter. Some are sold in standard sizes; others can be cut to fit old, odd-sized equipment by using the existing foam filter as a template.
In addition to improving the air quality, this will extend the life of the mechanism by keeping the working parts clean. For chronically humid houses -- common in the Southeast and anywhere the water table is high -- the basement dehumidifier is a vital appliance. These freestanding machines cost about $250 and switch on whenever an adjustable humidity meter, or hygrometer, registers excessive moisture in the air.
(A tip: Connect the dehumidifier's discharge pipe to a drain, and you won't have to empty the water bucket constantly.) In general, indoor humidity should not exceed 50 percent in a home. But, if the basement is dry and the house is generally free of mold and excessive dust, occasional problems can be as simple to solve as opening a few windows on a mild day.