1. Inspect your furnace and duct work. Check to make sure there's ample open space around your furnace, removing any flammable materials from the area. Inspect your house's cold air return vents—they should be open and free of obstruction (blocked vents contribute to inefficient combustion and the danger of carbon monoxide poisoning). Examine your ducts for holes, loose joints, and deterioration by beginning at the furnace and working outward towards each register. If you spot gaps, use duct tape as a temporary fix.

If your furnace or air conditioner is over five years old, AAA highly recommends professional inspections every two years to identify less obvious problems. Consult your local phone book for a qualified technician who will examine thermostats, vents, flues, seals, chimneys, connectors and ductwork.

Remember that dust build-up inside your ducts can provide a home for air-borne mold, mildew and bacteria. If the inspection reveals dirty ducts, contact a professional duct cleaning service.

2. Change your air filters regularly. During periods of use air filters can quickly become clogged, limiting your furnace's air supply. Cleaning your air filters also helps prevent the spread of air-borne mold and mildew. Here are some general guidelines for maintenance on various types of filters:

• Examine fiberglass filters once a month during the heating and cooling seasons, replacing filters when dust build-up becomes evident.
• Pleated filters can last up to three months.
• Wash and rinse permanent filters monthly.
• Clean electronic air-cleaner filters every other month.

3. Clean your chimney annually. The Chimney Safety Institute of America recommends that open masonry fireplaces should be cleaned after soot builds up to 1/4", and sooner if there is any glaze present in the system. Factory-built fireplaces should be cleaned when any appreciable buildup occurs. This is considered to be enough fuel buildup to cause a chimney fire capable of damaging the chimney or spreading to the home.

Even if both your furnace and fireplace use gas, your chimney still needs regular attention to ensure efficient passage of exhaust. Keep chimney vents and flues free from bird nests or other debris, and have them inspected professionally every three years.

4. Monitor indoor humidity levels, correct if necessary. For most homes, a humidity level of 30-50% is desirable. Higher moisture levels in your home's air can provide favorable conditions for the growth of mold and mildew and may lead to structural damage from rot. And once established, mold and mildew can be difficult, even impossible, to eradicate. Thankfully, prevention is fairly simple.

Warning signs of high humidity:

• Condensation on windows
• Wet stains on walls and ceilings
• A persistently moldy bathroom
• Musty smells

Tips to decrease humidity in your home:

• Open windows regularly to increase ventilation.
• Install kitchen and bathroom exhaust ventilation fans and run them often.
• Make sure your clothes dryer vents outdoors, and dry clothes on an outdoor line whenever possible.
• Use a portable dehumidifier.

If these steps still aren't enough, consult a heating/cooling professional for an appropriate solution.

Download the EPA's "Guide to Mold Mildew and Your Home"

5. Prevent CO Poisoning. Carbon monoxide (CO) is produced whenever any fuel such as gas, oil, kerosene, wood, or charcoal is burned. If you heat with gas or oil, or have other gas appliances (like a dryer or stove) you should pay special attention to the threat posed by CO poisoning. You can't see or smell carbon monoxide, but at high levels it can kill a person in minutes. If appliances are not working properly or are used incorrectly, dangerous levels of CO can accumulate.

Ask your furnace technician to inspect for conditions that can lead to CO poisoning, e.g., inefficient combustion, leaky duct seams, and blocked air return vents, and to test for the presence of CO. For added peace of mind you may want to consider installing a CO detector (many models available at hardware stores now cost under $50).

Other CO tips:

• When using your gas stove top, be sure to run the exhaust fan.
• Never use unvented gas or kerosene space heaters inside your house, even if the manufacture claims it is safe to do so.
• If your garage is attached to your house, never leave the car running while it's in the garage.
• If you heat with a gas or wood burning stove, inspect the stove regularly as directed by the manufacturer.

6. Know how to turn off the gas. In an emergency it may be necessary to shut the main gas valve to your house. Do you and the other members of your household know how?