What to buy
Minimum requirements for any US residential CO detector:
- UL 2034 listed — the residential CO detector standard
- End-of-life signal — modern UL-listed units chirp when they reach replacement age (typically 7–10 years)
- Digital display — useful for diagnosing low-level CO before alarm threshold
- Battery backup for hardwired units; sealed battery (10-year) for battery-only units
Battery-only vs hardwired
- Battery-only: easier installation, works during power outages, but battery replacement is a recurring task. Sealed 10-year battery units reduce this burden.
- Hardwired with battery backup: never has dead batteries unless backup also fails. Required by code in many new-construction US jurisdictions.
- Interconnected smoke + CO: when one detector alarms, all detectors alarm. Strongest option but requires retrofit wiring in existing homes.
Placement
- Every occupied floor of the home
- Outside every sleeping area
- Near (but not directly above) combustion appliances — furnace, water heater, gas range
- 5–6 ft from the floor — CO mixes with air; doesn't sink or rise
- Not near windows, vents, or extreme temperature areas — false alarms
- Not directly above propane burners — high heat or temperature swings interfere with sensors
Replacement schedule
CO detector sensors degrade with time and exposure. Manufacturer-rated lifespan: 7–10 years. Modern UL-listed detectors chirp when they reach end-of-life — don't ignore this. Replace per the manufacturer schedule, not based on whether the detector 'still works' (sensor accuracy degrades before total failure).
Combination smoke + CO units
Two-in-one smoke and CO detectors are increasingly popular. Pros: fewer devices to manage, lower total cost vs separate units. Cons: when one sensor element fails, you lose both functions. For best protection, separate dedicated units on each floor — combination units acceptable if budget is a constraint.
FAQ
How many CO detectors do I need?
Minimum: one per occupied floor, one outside every sleeping area. For a typical 3-bedroom 2-story US home with basement: 3–4 detectors total.
Are CO detectors required by law?
Required in residential buildings by most US state and many local codes — though specific requirements vary. New construction is more strictly regulated than existing homes. Required or not, CO detectors are essential safety equipment in any propane-using home.