Home CO Sensors by Rooms

Residential carbon monoxide (CO) detector sizing

You can't see, smell or taste carbon monoxide, which is exactly what makes it dangerous. It comes from fuel that doesn't burn completely — natural gas, propane, gasoline, wood, charcoal. The rule we follow here is one detector per floor, then add one near anything that burns fuel: N = floors + sources. Count water heaters, gas stoves, fireplaces, wood stoves and any garage attached to the house as sources.

NFPA 720 (now folded into NFPA 72) lays out the bare minimum. Put a detector outside each sleeping area, one on every habitable level, and one within 3 m (10 ft) of any fuel-burning appliance. A UL 2034 listed unit has to alarm somewhere in the 60–240 min window at 70 ppm, and within 35 min at 200 ppm. The electrochemical cell wears out, so plan to swap the whole unit every 5–7 years. Check the manufacture date stamped on the back — the battery isn't the part that expires.

Applications

Homeowners reach for this when commissioning a new gas appliance. Landlords use it prepping rentals for occupancy permits, and home inspectors when bringing an older house up to code. Several U.S. states (CA, MA, NY) and Canadian provinces (ON, BC) make CO alarms a legal requirement in any dwelling that has an attached garage or burns fuel.

FAQ

Where exactly should I mount the detector? Either at breathing height (about 1.5 m off the floor) or on the ceiling. CO mixes evenly with air, so it doesn't collect high or low the way smoke does. Stay away from corners, the space behind curtains, and anything closer than 1.5 m to a cooking appliance, which tends to set off false alarms.

What CO concentration is dangerous? OSHA caps the 8-hour exposure at 35 ppm. By 200 ppm you get headaches within 2–3 h; at 800 ppm people lose consciousness inside 2 h. Once carboxyhemoglobin (HbCO) saturation climbs past 40%, it's often fatal.

Smoke detector and CO detector — same thing? No. A smoke detector runs on a photoelectric or ionization sensor, while a CO detector relies on an electrochemical cell. There are combination units (Kidde, First Alert) that handle both jobs and meet NFPA 72 and NFPA 720 at once.