Silent Killer: Prevention of Carbon Monoxide
Carbon monoxide (CO) is an odorless, colorless gas produced any time a fuel like natural gas, propane, or oil burns. Inside a healthy furnace or boiler, it is contained in the heat exchanger and vented safely out of the home. When a heat exchanger cracks, that combustion gas can escape into the air you breathe, which is why CO is often called the silent killer.
In southern New Hampshire, where most homes still run on gas, propane, or oil heat through long winters, annual combustion safety checks are one of the most important things a homeowner can stay on top of. At A.J. LeBlanc Heating, we have been helping NH families heat their homes safely since 1928.
What a heat exchanger is and why it matters
The heat exchanger is the metal chamber inside a furnace or boiler where combustion happens. In a forced-air furnace, air from your ductwork passes over the outside of the heat exchanger and picks up heat from the hot metal. The combustion gases stay sealed inside and exit through the flue.
That separation between the air you breathe and the combustion gases is what makes the heat exchanger the single most important safety component in a fuel-burning system. When the metal cracks, the seal is broken.
How heat exchangers fail
Most heat exchanger failures share a common cause: years of restricted airflow that overheats and weakens the metal. Common contributors include:
- A dirty or clogged air filter left in place too long
- Blocked supply or return vents
- An oversized furnace that short-cycles and stresses the metal
- A blower wheel coated in dust, reducing airflow over the exchanger
- Age: simple metal fatigue from decades of heat-cool cycles
As the metal weakens, small stress cracks form. Many cracks are too small to see without a borescope or combustion test, which is why visual inspection alone is not enough.
Warning signs to take seriously
Carbon monoxide does not give you obvious symptoms in the home, but the heating system itself sometimes does. Call for service if you notice:
- Soot or scorch marks on or near the furnace
- A yellow or flickering burner flame instead of a steady blue one
- An unusual sharp or chemical smell when the system runs
- Excessive condensation on windows when the heat is on
- Headaches, dizziness, or nausea that improve when you leave the house
The last item is the most important. Symptoms that get better outside and come back when you return home are a classic CO exposure pattern. If you suspect it, leave the home and call 911 from outside.
CO detectors: placement and replacement
New Hampshire requires CO detectors in homes built or substantially renovated since 2010 and in all rental units; we strongly recommend them in every home with a fuel-burning appliance or attached garage regardless of age. A few placement basics:
- Install at least one CO detector on every level of the home
- Place one within 10 to 15 feet of every sleeping area
- Mount on the wall about five feet off the floor, or on the ceiling at least six inches from the wall
- Do not mount directly above a fuel-burning appliance or inside a closet with the furnace
CO sensors have a finite life. Most detectors are rated for seven to ten years from the date of manufacture, regardless of battery condition. Check the back of the unit for a manufacture date and replace accordingly. Test all alarms monthly.
How to prevent heat exchanger failure
Most heat exchanger failures are preventable with two habits:
- Change your air filter regularly. Every one to three months for a 1-inch filter, every six to twelve months for a 4 to 5-inch media filter.
- Have the system serviced annually by a licensed technician who performs a combustion analysis and inspects the heat exchanger. This catches problems before they become safety issues.
An annual safety inspection includes draft testing, combustion analysis with measured CO and CO2 readings, flame inspection, and a borescope or visual heat exchanger check on systems where access allows.
If your furnace is condemned
If a technician finds a cracked heat exchanger, the system will typically be red-tagged and shut down. This is not a sales tactic. A compromised heat exchanger on a fuel-burning system is a real safety issue, and continuing to operate it is genuinely dangerous. We will walk you through your repair or replacement options and help you understand the trade-offs.
Schedule a safety check
If your heating system has not been inspected in over a year, or you are seeing any of the warning signs above, do not wait. Contact A.J. LeBlanc Heating to schedule a safety inspection. Serving New Hampshire families since 1928.
Frequently Asked Questions
Can carbon monoxide come from a clean, new furnace?
Properly installed and vented modern furnaces produce negligible CO inside the home. Problems typically arise from a cracked heat exchanger, blocked vent, or improper installation. Annual combustion analysis is the most reliable way to confirm safe operation.
How often should I replace my CO detector?
Every seven to ten years, based on the manufacture date printed on the unit. Test monthly and replace batteries at least annually.
Is a CO leak only a concern with gas furnaces?
No. Any fuel-burning appliance can produce CO, including oil furnaces, propane heaters, gas water heaters, wood stoves, fireplaces, and gas ranges. An attached garage with a running vehicle is another common CO source.
What level of CO is dangerous?
Concentrations as low as 50 parts per million over several hours can cause symptoms in sensitive individuals. Levels above 150 to 200 ppm can cause serious symptoms within a few hours. Detectors are designed to alarm well before levels become immediately dangerous.
What should I do if my CO alarm goes off?
Get everyone out of the home immediately, including pets. Call 911 from outside. Do not re-enter the home until emergency responders confirm it is safe. Then have your heating system inspected by a licensed technician before using it again.