Carbon Monoxide & Combustion Safety: What Every Homeowner Should Check

Carbon monoxide is a gas produced whenever fuel doesn’t burn completely. You can’t see it, smell it or taste it. That’s exactly what makes it dangerous. Your senses, which do a decent job warning you about smoke or spoiled food, give you no warning at all.

Once you breathe it in, CO crowds out the oxygen your blood is supposed to carry. The early symptoms are easy to mistake for something else. The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, and notes they’re often described as flu-like. People who are asleep can be overcome before they notice anything.

Anything that burns fuel inside your home, or in a garage attached to it, can produce carbon monoxide along with nitrogen dioxide and fine particles. The usual list:

• Gas, oil and propane furnaces and boilers
• Gas water heaters
• Gas ranges and ovens
• Gas fireplaces, wood fireplaces and wood stoves
• Gas clothes dryers
• Cars, generators and gas-powered equipment in an attached garage

Modern sealed-combustion equipment that’s installed and vented correctly handles this well. The risk comes from older or poorly vented appliances, blocked or disconnected flues, equipment that has drifted out of tune, and cracked heat exchangers in furnaces.

A furnace’s heat exchanger is the metal wall that keeps combustion gases separate from the air the blower sends through your house. After years of heating up and cooling down, it can crack. Warning signs include soot or scorch marks around the furnace, rust or moisture around the burners, a burner flame that wavers or changes when the blower kicks on, and a CO alarm that goes off when the heat is running. None of those prove a crack. Only an inspection by a qualified technician can confirm it, and it’s a check worth having every heating season.

One more rule with no exceptions: never run a generator, grill or car inside a garage, basement or any enclosed space, even with the door open.

The U.S. Consumer Product Safety Commission recommends CO alarms on every level of the home and outside sleeping areas. Test them monthly and replace the batteries once a year. Alarms wear out too, so check the date on the back and replace the unit when the manufacturer says to.

Standard alarms are built to a safety standard, UL 2034, that’s designed to avoid false alarms. That means a typical detector won’t sound at lower levels until you’ve been exposed for a while. It’ll catch a dangerous spike. It won’t tell you about a low, steady leak. That’s why I recommend a low-level CO monitor in any home with fuel-burning appliances. It shows you an actual reading and alerts well below where a standard alarm kicks in.

Beyond the alarms, a few things any homeowner can check:

• Keep the area around the furnace, boiler and water heater clear. They need air to burn properly.
• Look for soot, scorching or rust around appliances and where the vent pipes connect.
• Make sure outdoor vents and flues aren’t blocked by snow, leaves or nests.
• Have fuel-burning equipment checked every year, including a combustion and CO test, not just a filter change.

Some situations aren’t a call to schedule. They’re a call to get out.

• If a CO alarm sounds, get everyone, pets included, outside into fresh air right away. Then call 911 or the fire department from outside. Don’t go back in until responders say it’s safe.
• If anyone has symptoms like headache, dizziness, nausea or confusion that could be CO, get them outside and get medical help.
• If you smell gas, the rotten-egg odor added to natural gas, leave without flipping any switches and call your gas utility or 911 from outside.

Once the emergency is handled, whatever caused it needs to be inspected and repaired before it runs again. That’s where a heating company comes in. Have the furnace, water heater and venting checked by a technician who actually measures combustion and CO, not one who glances at it and leaves.