How many carbon monoxide detectors a unit needs

Carbon monoxide alarms became a named inspection item, and the question that follows is a counting question: how many does a unit need? The answer is not one per unit. It depends on sleeping areas and levels, and inspectors count the same way every time.

The sleeping area rule

The baseline is an alarm outside each separate sleeping area, in the immediate vicinity of the bedrooms it serves. A hallway serving three bedrooms is one sleeping area and takes one alarm. Two bedrooms at opposite ends of a unit, each off its own hallway, are two separate sleeping areas and take two alarms.

This is the rule that produces undercounts. Teams order one alarm per unit, install it centrally, and the unit with a split floor plan fails.

Levels

Multi level units require an alarm on each level, including levels without bedrooms. A townhouse style unit with bedrooms upstairs and living space downstairs needs coverage on both, and a finished basement counts as a level.

Where a level has its own sleeping area, both rules apply and the alarm serving the sleeping area can satisfy the level requirement for that level.

Units with no source

The requirement attaches to units with a fuel burning appliance or an attached garage. All electric units with no attached garage and no fuel burning appliance anywhere in the building generally fall outside it, but that determination should be documented at the property level rather than assumed by a technician in the field.

Common mistakes here run in one direction. A shared mechanical room with a gas water heater serving the building, or a common corridor connected to a garage, changes the analysis.

What inspectors verify

Presence in the required locations, operability when tested, correct mounting position per the manufacturer, and whether the device has passed its end of life date. A working alarm past its stamped expiration is still a deficiency.

Most failures are not missing devices. They are the right number of devices in the wrong places, or the right places with expired devices.

Sizing the order

Count by floor plan, not by unit. Pull the unit mix, count sleeping areas and levels for each plan type, and multiply. A portfolio ordering one per unit is short by ten to twenty percent in most mixes with townhouse or split plans.

Record model, install date, and end of life date by unit at installation. Replacement then becomes a scheduled item rather than a discovery during an inspection.

Combination smoke and carbon monoxide devices satisfy both requirements where they are installed in a location that both rules accept, which simplifies the count in single level units and does not remove the level requirement in multi level ones.