Carbon Monoxide Alarm Going Off? Get Out, Then an $80 Check
If your carbon monoxide alarm goes off, get everyone outside and call 911 from there, then have the furnace and other fuel-burning appliances checked; HomeAdvisor's 2026 guide puts a furnace inspection at $80 to $100.
Do not go back in until responders say it is safe, the CPSC says.
Do this now: carbon monoxide alarm going off
- Get everyone outside to fresh air, or to an open window or door if you cannot get out (NFPA). Do not look for the source first (CPSC).
- Account for everyone in the home (NFPA).
- Call 911 or the fire department from outside (CPSC). Say if anyone has a headache, dizziness, nausea, chest pain or confusion; the CDC lists those as symptoms of CO poisoning.
- Stay out until responders say it is safe to go back in (CPSC; NFPA).
- Do not run the furnace, water heater or other fuel-burning appliances again until a qualified technician has checked them. The CDC and CPSC both say these should be serviced by a professional.
Fire department cleared the house and pointed to the furnace or water heater? Call the heating and AC line for an inspection.
Our line is not an emergency service. If the alarm is sounding now, call 911 from outside, not us.
A carbon monoxide alarm sounds when it senses CO, a gas that cannot be seen or smelled, from fuel that burns incompletely. After responders clear the house, HomeAdvisor puts a furnace inspection at $80 to $100.
Is it an emergency? Alarm vs. chirp
A full alarm is always an emergency: on First Alert's CO5-B10D it is a repeating pattern of 4 beeps and a pause. A single chirp on a timer is usually a battery or end-of-life warning, not CO. Patterns vary by brand, so check the label or manual for yours.
| Sound | What it means | Source |
|---|---|---|
| Repeating 4 beeps, then a pause | Carbon monoxide detected: get out and call 911 | First Alert CO5-B10D manual |
| 5 chirps every minute | End of life: replace the alarm | First Alert CO5-B10D manual |
| Chirp every 30 seconds (Kidde combo alarms) | End of life or sensor error; a new battery will not stop it | Kidde |
| Chirp every 60 seconds (Kidde combo alarms) | Low battery | Kidde |
| Trouble signal that keeps sounding after new batteries | Call the fire department | NFPA |
If anyone feels sick, treat it as CO no matter what the alarm is doing: get out and call 911.
Carbon monoxide kills more than 400 Americans a year in poisonings not linked to fires and sends more than 100,000 to emergency rooms, the CDC says. NFPA counted an estimated 80,100 nonfire CO calls to U.S. fire departments in 2010, about nine an hour.
What causes carbon monoxide in a house
Fuel-burning equipment that is leaking, badly adjusted or venting back into the house causes most indoor CO, the EPA says. Its list of sources:
- Leaking chimneys and furnaces, and back-drafting from furnaces, gas water heaters, wood stoves and fireplaces.
- Unvented kerosene and gas space heaters.
- Gas stoves. EPA says levels near a poorly adjusted gas stove can reach 30 ppm or more, against 0.5 to 5 ppm in homes without gas stoves.
- Generators and other gasoline-powered equipment. The CDC says to run a generator outdoors, more than 20 feet from windows, doors and vents.
- Car exhaust from an attached garage. Never leave a vehicle running in it (CDC).
- Tobacco smoke.
If the furnace is also blowing cold air, mention it when you book the inspection. A boiler or water heater can be the source too: see boiler repair and water heater repair. A blocked flue may need chimney repair.
Furnace and appliance inspection cost after a CO alarm
A furnace inspection costs $80 to $100 and a full tune-up $125 to $200, HomeAdvisor's June 2026 guide says; HomeGuide puts a tune-up at $70 to $200. The CPSC says every fuel-burning heating system, including furnaces, boilers, water heaters, fireplaces, chimneys and vents, should be inspected by a professional once a year.
| Service | Published price | Source |
|---|---|---|
| Furnace inspection | $80 to $100 | HomeAdvisor, June 2026 |
| Furnace tune-up | $125 to $200 | HomeAdvisor, June 2026 |
| Furnace tune-up | $70 to $200 | HomeGuide, Aug 2025 |
| HVAC inspection | $150 to $500 | HomeGuide, July 2025 |
| Chimney inspection, Level 1 / Level 2 | $100 to $250 / $250 to $600 | HomeGuide, Feb 2026 |
| Furnace repair, average | $318 ($133 to $505) | HomeAdvisor, June 2026 |
| Heat exchanger | $100 to $1,500 | HomeAdvisor, June 2026 |
| Heat exchanger | $1,000 to $3,000 | HomeGuide, Aug 2025 |
Inspection prices are for a routine visit. A technician who finds a cracked heat exchanger or a blocked vent will quote the repair separately.
A cracked heat exchanger is the costly finding. HomeGuide says most technicians replace a heat exchanger rather than repair it because of the risk of CO leaks. HomeAdvisor's rule of thumb: if the repair quote is more than half the price of a new furnace, start shopping. See how long a furnace lasts, furnace repair and furnace replacement cost.
Need the furnace and water heater checked after a CO alarm? Call the heating and AC line and say what the fire department found.
How long do CO detectors last
Most carbon monoxide detectors last 5 to 10 years: the CDC says replace them per the manufacturer or about every 5 years, and First Alert and Kidde rate current models for 10. Kidde says the manufacture date is on the back of the alarm.
| Source | Replacement guidance |
|---|---|
| CDC | Replace per the manufacturer, or about every 5 years |
| First Alert (CO5-B10D) | After 10 years or at the end-of-life signal, whichever comes first |
| Kidde | 10 years for alarms made in 2013 or later; 7 years for older ones |
| NFPA | Test monthly and replace as the manufacturer directs |
Kidde says end-of-life chirps do not stop after a battery change. The manufacture date is printed on the back of the alarm.
Where to put carbon monoxide alarms
Put a CO alarm on every level of the home and outside each sleeping area, the CPSC and NFPA say. NFPA says to interconnect them so that when one sounds they all do, and the CDC recommends battery-operated or battery-backup models so they work in a power outage.
Portable generators belong outdoors, more than 20 feet from windows, doors and vents (CDC); standby generator installation covers permanent outdoor units. A gas smell is a different problem: see what a gas leak smells like. After-hours heating calls are on emergency HVAC repair, the HVAC repair hub lists other jobs, and home repair costs compares prices.
Calls go to an independent company that serves your area and takes this kind of job. Ask for its license number and proof of insurance before work starts. Some companies take emergency calls; hours vary. How calls work.
Related winter and safety guides
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Questions people ask
What should I do if my carbon monoxide alarm goes off?
Get everyone outside to fresh air, then call 911 or the fire department from there, the CPSC says. Do not search for the source, and stay out until responders say it is safe.
What causes carbon monoxide in a house?
The EPA lists leaking chimneys and furnaces, back-drafting from furnaces, water heaters, wood stoves and fireplaces, unvented space heaters, gas stoves, generators, car exhaust from an attached garage and tobacco smoke.
Why is my carbon monoxide detector chirping?
A timed chirp usually means a low battery or end of life, not CO. First Alert's CO5-B10D gives 5 chirps a minute at end of life; on Kidde combo alarms a chirp every 30 seconds means end of life or a sensor error.
How long do CO detectors last?
The CDC says replace them per the manufacturer or about every 5 years. First Alert and Kidde rate current models for 10 years; Kidde alarms made before 2013 last 7.
How much does a furnace inspection cost after a CO alarm?
HomeAdvisor puts a furnace inspection at $80 to $100 and a tune-up at $125 to $200. HomeGuide lists a tune-up at $70 to $200.
Can I go back inside after the CO alarm stops?
Not until emergency responders say it is safe, the CPSC and NFPA say. Wait in fresh air until then.
House cleared by the fire department? Call the heating and AC line to have the furnace and water heater inspected. Alarm sounding now? Get out and call 911.
- 1Call the line
- 2It rings a local company
- 3They give you the price
Before you book
- License numberAsk for it, then check it with the state board.
- Written priceGet the visit fee and the job price in writing before work starts.
- Proof of insuranceAsk for the certificate, especially for roof, tree and electrical work.
Sources (12)
- CPSC: Carbon Monoxide Fact Sheet (checked 2026-10-11)
- CPSC: Carbon Monoxide Information Center (checked 2026-10-11)
- CPSC: Home Heating Equipment (checked 2026-10-11)
- CDC: Carbon Monoxide Poisoning Basics (2026-01-12)
- EPA: Carbon Monoxide's Impact on Indoor Air Quality (2026-07-15)
- NFPA: Carbon Monoxide Safety tip sheet (copy hosted by the Village of Penn Yan) (2017)
- First Alert: CO5-B10D carbon monoxide alarm user manual (2026-03)
- Kidde: Carbon Monoxide Detector Replacement FAQs (checked 2026-10-11)
- HomeAdvisor: How Much Does Furnace Repair Cost in 2026? (2026-06-20)
- HomeGuide: How Much Does Furnace Repair Cost? (2026) (2025-08-27)
- HomeGuide: How Much Does HVAC Repair, Service, and Maintenance Cost? (2026) (2025-07-31)
- HomeGuide: How Much Does a Chimney Sweep Cost? (2026-02-09)
Talk to an HVAC tech who serves your area
Have the address, the system type (furnace, boiler, heat pump or central air), the brand and age if you know them, and what it is doing. The company will quote its service call fee before anyone is sent.
Free call to an independent company in your area that takes this kind of work.