Mistake: You warm up your car... in the garage

Even with the garage door open, it's dangerous to run an automobile in a garage - especially one attached to the house. When you step from your house into your garage, a wall of cold air rushes through the door. That's when deadly carbon monoxide - or vapors from open paints, solvents, or pesticides - can make their way in.

Fix it: Reduce fumes and seal entrances.
Install a self-closing door (or put springs on your existing one) so it's never left open by mistake.  And make sure all doorways - and any cracks leading to the first floor or to a room above the garage - are airtight.  Most importantly, never run the car in the garage!

Check it: Your furnace
Faulty heating systems are the leading cause of carbon monoxide poisoning in the home, so have yours examined professionally before turning it on each year, especially if it's more than 5 years old.

Mistake: Your home's been cleared for lead... but not radon

The dangers of lead poisoning are well-known, and lead paint has been phased out of housing construction nationwide. But few states regulate another contaminant—the leading cause of lung cancer after cigarette smoking: radon.  Nearly 1 out of 15 homes in the United States is estimated to have elevated levels of the radioactive gas that can seep from soil into a home's foundation.  (Find more details about your county at epa.gov/radon/zonemap.html.)

Fix it: Test your levels.
Low-cost kits that measure radon for about a week are available at hardware stores or by calling (800) 767-7236. Keep windows closed and place the kit at your home's lowest surface for an accurate reading.  If your levels are 4 pCi/L (picocuries per liter of air) or higher, test again.

Schedule it: An appointment with a specialist
If results are the same, call your state radon office (find yours via epa.gov/radon/radontest.html) and arrange for follow-up tests.  You may need to install a ventilation system.   Or it could be as simple as sealing cracks or areas where pipes enter the home.

Access Denied

Check these items at the door to help keep your home's air clean.

Cigarettes
It's not just smoke that dirties the air - it's the particles on smokers' clothing, too.  If a guest must step outside for a cigarette, ask her to wear a "smoking jacket" that stays out in a breezeway or garage.

Dry cleaning
Traditional cleaners use perchloroethylene, a chemical shown to cause cancer in animals. Look for a shop that uses silicone or carbon dioxide instead (some are listed at greenearthcleaning.com and findco2.com)—and air your unbagged garments outside for 3 hours before putting them in your closet.

Shoes
Outside, the sun and the elements break down pesticides; when they're tracked indoors, they stick around in your carpet and make their way into the air.  Keep a shoe rack and basket of slippers by the door for quick changes.

Firewood
When burned, even untreated logs release harmful gases and tiny particles that get into the lungs and bloodstream. Use your fireplace sparingly with artificial timber—like Duraflame's All Natural Firelog - or, better yet, switch to gas.