St. Louis Carbon Monoxide Detector Installation

What Sets Off a Carbon Monoxide Alarm

A listed alarm responds to a concentration held over time. Under UL 2034, a residential unit has to sound within 60 to 240 minutes at 70 parts per million and within 4 to 15 minutes at 400 ppm. That means a slow leak trips one as reliably as a sudden one, only later.

The sources behind a sounding alarm are usually these:

• A gas furnace or water heater venting poorly – A cracked heat exchanger, a loose vent connector, or a blocked masonry flue where the furnace and water heater share one chimney.
• A portable generator running too close to the house – An open garage or a spot under a window pulls exhaust back inside. We install Generac standby generators sited outdoors and wired to a transfer switch.
• A car left running in an attached garage – Exhaust travels through the common wall and door, which is why postwar ranch and split-level houses need an alarm on that level.
• Unvented heaters, ranges, and fireplaces – A kerosene heater, an oven used for warmth during an ice storm, or a damper left partly closed.

A unit past its sensor life gives you nothing while the source keeps running, so we check the age and mounting of every alarm while we're there.

Where Carbon Monoxide Detectors Belong in the House

Every floor needs one, the basement included, plus an alarm within ten feet of each bedroom door. Carbon monoxide mixes evenly with room air rather than rising as smoke does, so mounting height matters less than distance from the equipment.

Keep alarms 15 to 20 feet from a furnace, water heater, or fireplace. Any closer and ordinary startup combustion sets them off, which is how a working alarm ends up unplugged in a kitchen drawer. Note that a ceiling corner or a spot beside a supply register sits in dead air and reads late.

The City of St. Louis requires approved detectors in residential buildings with a fossil-fuel heat source or fossil-fuel machinery under Ordinance 63842. Requirements past the city line vary, so we confirm the jurisdiction before quoting.

Choosing an Alarm That Still Works in Five Years

The brand on the box matters less than four features you can check before you buy.

Look for these when you shop, or when we spec the units for your house:

• A printed end-of-life date – The electrochemical sensor degrades whether the alarm ever sees gas, and most units are finished five to ten years from manufacture.
• A digital display in parts per million – The number shows a low chronic level long before the alarm point.
• Hardwired power with battery backup – Wired units keep working after a battery dies, and plug-in models are the fallback where no circuit reaches.
• Combination smoke and carbon monoxide units – One device covers smoke and gas from a single ceiling box. Our smoke detector installation page covers the fire side.

We spec the units against the fuel-burning equipment in your house and wire them in one visit, at a flat rate settled in writing first.

Frequently Asked Questions About Carbon Monoxide Detectors

Homeowners ask the following questions after an alarm sounds and the fire department clears the house. Part of the answer belongs to a heating contractor rather than an electrician, and we say which is which on the phone.

What Should You Do When a Carbon Monoxide Alarm Goes Off?

Get everyone and any pets outside into fresh air, then call 911 from where you're standing. Leave the doors and windows as they are, since responders will want to measure what the house was holding.

Is a Carbon Dioxide Detector the Same as a Carbon Monoxide Detector?

No. Carbon dioxide is what you exhale, and carbon monoxide is a product of fuel that didn't burn completely. A CO alarm won't respond to carbon dioxide, and a CO2 monitor sold for a greenhouse won't warn you about a bad flue.

Does an All-Electric House Need a Carbon Monoxide Alarm?

If the house has an attached garage, yes. A car or a gas-powered mower running in that space pushes exhaust through the common wall. A detached garage with no gas service and no fireplace is the one case where the risk is low.