When does a house need a carbon monoxide alarm?
CO alarms are required in dwellings that contain a fuel-fired appliance or have an attached garage (IRC R315.2, 2015 edition).
The IRC requires carbon monoxide alarms in dwelling units that contain a fuel-burning appliance (gas, oil, wood, etc.) or that have an attached garage, since both are potential sources of carbon monoxide. (This is Section R315.2 in the 2015 IRC; earlier editions place the rule under R315.1.)
All-electric homes with no fuel-fired appliances and no attached garage are generally not required to have CO alarms under the base code, although local amendments can be stricter.
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