How do you know if your furnace is putting out carbon monoxide?

Author: Mellie O'Connell  |  Last update: Tuesday, February 10, 2026

Heavy condensation on the windows (found in the room with your furnace) Yellow or brown soot-like stains found around your furnace. A yellow pilot light (instead of a blue flame) Stuffy indoor air.

How do you tell if your furnace is giving off carbon monoxide?

Signs of a Furnace Carbon Monoxide Leak

These signs may include frequent pilot light blow-outs, soot accumulation in the fireplaces, smears of yellow/brown stains near appliances, duller than normal flames from their fires as well as noticeable smells like stale air and burning.

What are the symptoms of carbon monoxide poisoning from a heater?

Key points about carbon monoxide poisoning

A common source is unvented space heaters. Symptoms of CO poisoning include headache, dizziness, weakness, nausea and vomiting, rapid heartbeat, shortness of breath, seizures, chest pain, disorientation, and loss of consciousness.

Can a furnace leak carbon monoxide when not running?

One must remember that a furnace that is not running cannot generate carbon monoxide. This does not mean, however, that your home would be safe from exposure to CO anytime your furnace is turned off. The HVAC system, when it's not running, could distribute carbon monoxide if it is introduced into the system elsewhere.

What causes a furnace to produce carbon monoxide?

Carbon monoxide can become a problem if your furnace develops cracks in the heat exchanger. When heat exchangers rust, they become brittle. As they heat up and expand, cracks can start forming in the rusty metal, which allow carbon monoxide to leak through.

Furnace FAIL: Massive Carbon Monoxide Problem Tested from Home's Roof

How do you test a furnace for carbon monoxide?

According to the CDC, carbon monoxide is a silent killer that takes hundreds of lives per year. Unfortunately, you cannot tell just by looking at your furnace whether it is leaking carbon monoxide. You need a carbon monoxide detector or other special equipment to test the levels yourself.

How long does it take for carbon monoxide to build up in a house?

Small carbon monoxide leaks can fill every room in your house with poisonous gas within eight hours. Severe leaks can cause this problem in just five minutes. The EPA states that exposure to concentrations of nine ppm or more for eight hours is enough to produce harmful health effects for at-risk individuals.

How to tell if there is carbon monoxide?

It is also a good idea to know the signs of a potential CO problem:
  1. Streaks of soot around fuel-burning appliances, or fallen soot in a fireplace.
  2. Absence of an upward draft in your chimney.
  3. Excess moisture and condensation on windows, walls and cold surfaces.
  4. Rusting on flue pipes or appliance jacks.

How do you prevent carbon monoxide poisoning from a furnace?

Maintain appliances and equipment in good order. Have a certified heating and ventilation technician check your furnace for proper ventilation and exhaust. Install carbon monoxide monitors and regularly test the air in areas where carbon monoxide is generated. Check monitors monthly for proper function.

Can carbon monoxide leak if heating is off?

Your boiler won't be able to produce carbon monoxide when it's switched off because it isn't burning any fuel. However, if you think you may have a carbon monoxide leak, you should switch off your gas supply at the mains.

How to detect carbon monoxide without a detector?

Signs of carbon monoxide:
  1. Stuffy or stale air.
  2. A pilot light keeps going out.
  3. More condensation than usual on your windows.
  4. Soot build up around a fireplace, chimney, or other fuel-burning equipment.
  5. Fuel-burning equipment has a back-draft (flame flares up when a window or door opens and adds air).

Will opening a window help with carbon monoxide?

If you experience symptoms that you think could be from CO poisoning: DO GET FRESH AIR IMMEDIATELY. Open doors and windows, turn off combustion appliances and leave the house.

How do I use my iPhone to detect carbon monoxide?

Go to the Home app on your iPhone or iPad. , then tap Home Settings. Tap Safety & Security. Tap Sound Recognition, then turn on Smoke & CO Alarm.

How to tell if a furnace is leaking gas?

If you detect any of the following signs of a natural gas leak in your house or think you have been exposed, contact 911 immediately.
  1. The smell of rotten eggs. In its natural state, natural gas is odorless and colorless. ...
  2. Hissing sounds. ...
  3. Air bubbles outside your home. ...
  4. Dead or dying plants. ...
  5. Higher-than-normal gas usage.

How to test a carbon monoxide alarm?

How to test your carbon monoxide detectors to ensure they are working properly? To test your carbon monoxide detectors, press and hold the test button on the alarm. The detector will sound 4 beeps, a pause, then 4 beeps for 5-6 seconds. Refer to the user manual for your specific model.

Will turning off the gas stop carbon monoxide?

If your boiler is switched off at the mains, your boiler will not be burning fuel and therefore no waste carbon monoxide gas will be produced.

How to tell if your furnace is giving off carbon monoxide?

The soot stain can have a black, brown or even yellow color. Smell: While carbon monoxide doesn't emit odor, it may get accompanied by other exhaust gases that produce an odor. A yellow burner flame: The pilot flame may produce an unusual yellow flame instead of the normal blue one.

What appliances give off carbon monoxide?

CO is primarily produced by the improper operation or ventilation of appliances such as furnaces, water heaters, ovens, fireplaces, fuel space heaters, generators, and charcoal grills that are fueled by oil, propane, natural gas, wood, kerosene, gasoline, and diesel.

What happens if my carbon monoxide alarm goes off?

If anyone has flu-like symptoms, contact 911 and get outside for fresh air. The types of sounds and beeps the detector makes are important. Alarms that are continuously going off with a high-pitched sound mean there is a carbon monoxide leak. Contact your emergency service provider immediately.

Is there a way to test for carbon monoxide at home?

Here are the best ways to conduct a carbon monoxide test.
  1. Electronic Carbon Monoxide Detector. This type of CO detector can be hard-wired to your electrical system like a smoke alarm. ...
  2. Battery-Operated Carbon Monoxide Detector. ...
  3. Portable Carbon Monoxide Meter. ...
  4. Professional Carbon Monoxide Air Test. ...
  5. Litmus Paper.

Should I call 911 if my carbon monoxide alarm goes off?

My carbon monoxide alarm is sounding. What should I do? Call 911 and report what is happening. Immediately leave your residence and wait for the fire department to arrive.

How to tell if your house is toxic?

If you suspect your asthma worsens or is more severe than usual, contact your doctor or medical professional.
  1. Bad Smells In The Home. When there's a bad smell in the home, you can tell. ...
  2. Peeling Wallpaper. ...
  3. Spots On The Wall. ...
  4. Bad Allergies Won't Go Away. ...
  5. Visible Mold Growth. ...
  6. Past Water Damage.

Can opening a window stop carbon monoxide poisoning?

If you think you might have carbon monoxide poisoning: stop using appliances you think might be making carbon monoxide (such as a boiler, cooker or heater) if you can. open any windows and doors to let fresh air in.

How do I know if my house is filling with carbon monoxide?

Any of the following could be a sign of a carbon monoxide leak: Floppy yellow or orange flame on your gas hob or oven, rather than a crisp blue flame. Dark, sooty staining on or around gas appliances. Pilot lights that frequently blow out.

Can dogs smell carbon monoxide?

Carbon monoxide, commonly known as CO, is an odorless, colorless, and non-irritating gas. No pet can identify the gas because CO lacks any scent whatsoever. Exposure can lead to carbon monoxide poisoning in both humans and pets.

Previous article
Do I need to turn off breaker to install smoke detector?
Next article
Is new flooring a capital improvement?