Should I?Reviewed: 2025-12-27~1 min

Should I test a carbon monoxide detector before turning on gas heating for the season?

Short answer

ℹ️Quick answer

Yes. Testing your carbon monoxide detector right before the first seasonal startup helps catch issues that often appear after equipment sits idle.

Why people ask this

People ask this when they’re about to start their furnace after months of downtime. Seasonal startups are when vents, burners, or heat exchangers are most likely to have issues like dust buildup or blocked flues. A quick test ensures your alarm will sound if your gas furnace, boiler, or gas fireplace releases CO on first ignition. It also confirms batteries and sensor life are still good after the off-season.

When it might be safe

You tested all CO alarms within the last month and verified audible alarm, power, and end-of-life dates, specifically in areas near the furnace and sleeping rooms.
You just installed new, in-date CO detectors this season and confirmed they are interconnected or monitored.
You have a professionally monitored, hardwired CO system that was function-tested during a recent HVAC preseason tune-up.

When it is not safe

Starting the gas furnace after summer without verifying the CO alarm sounds and has fresh batteries or stable power.
Ignoring a detector’s chirps, low-battery alerts, or end-of-life warning before first heat.
Relying on a single detector far from the furnace or sleeping areas during the first startup.
Using an older detector past its sensor life (often 5–7 years) at the start of heating season.
Running the first heat cycle with vents or flues potentially blocked by leaves, nests, or debris without CO protection.

Possible risks

Undetected CO from a misadjusted burner or cracked heat exchanger that shows up on the first few heat cycles of the season.
Backdrafting or blocked flues after months of inactivity, causing CO to spill into living spaces.
Reduced detector performance due to expired sensors or drained batteries after the off-season.
Nighttime exposure if CO accumulates when the thermostat calls for heat overnight and alarms aren’t functioning.
Delayed response when the only detector is too far from bedrooms or the furnace room during initial startup.

Safer alternatives

Schedule a preseason HVAC tune-up that includes combustion analysis and a CO safety check at startup.
Add a low-level CO monitor alongside standard CO alarms for more sensitive detection during first runs.
Use interconnected or professionally monitored CO alarms so any single alarm triggers a full-home alert on first heat.
Place at least one CO alarm near sleeping areas and another on the level with the furnace before turning heat on.
If you use multiple gas appliances (furnace, boiler, gas fireplace), test CO alarms just before lighting each one for the season.

Bottom line

Yes—give your CO detector a quick test and confirm power, batteries, and sensor age before the first heat of the season. Seasonal startups are when hidden venting and combustion issues are most likely, and a working alarm is your simple safety backstop.