Q&A: Installing Smoke Detectors

A.Art Laurenson, a Providence, R.I., firefighter and assistant deputy state fire marshal, responds: To be sure you are complying with local regulations, contact your local electrical inspector and the local fire department. For new construction, BOCA and NFPA 70 (the National Electrical Code) both require hard-wired, interconnected devices with battery back-up.

Residential smoke alarms should be wired on a dedicated circuit. It’s a good idea to have at least one light or receptacle-on the same circuit, to alert the homeowners in case the circuit breaker ever trips. Interconnected alarms are usually wired in a daisy chain, using 14-3 or 12-3 cable. The third conductor is the communication wire.

Some installation guidelines:

• As a minimum, one device is required on every occupiable level of the house.
• At wall-ceiling intersections, there tends to be a dead space where smoke doesn’t accumulate, so smoke detectors shouldn’t be located in corners. While smoke-detector manufacturers allow the devices to be located as close as 4 inches to the wall-ceiling intersection, some codes require that a ceiling-mounted smoke detector be located at least 12 inches from a wall and that the top of a wall-mounted smoke detector be located 6 to 8 inches from the ceiling.
• Install a separate smoke detector in each bedroom and one in the common hallway near the bedrooms.
• In most cases, a smoke detector should not be located in a kitchen. The best device for use near a kitchen is a smoke detector with a hush mechanism, like the Firex model 4518 or 4618 (Maple Chase Co., 800/951-5526; www.maplechase.com) or the First Alert model 4120 SB (800/323-9005; www.firstalert.com). The hush mechanism disables the alarm circuit while keeping the sensing circuit active. If the amount of smoke continues to increase, the device will sound again.
• An attic accessible by stairs (as opposed to a ladder) needs a smoke detector. Although NFPA 70 exempts unfinished attics, an attic with stairs might be used by children to play in.
• A basement is considered an occupiable level and requires a smoke detector. If the stair is open (with no walls), the smoke detector should be installed at the top of the stairs. If the stair is closed (with walls on both sides), the smoke detector should be installed at the basement ceiling near the bottom of the stairs.
• Although not required by most codes, added protection can be achieved by installing a heat detector near the furnace or boiler and in the garage. These heat detectors should be interconnected with the house smoke detectors.
• Large houses may need additional smoke detectors. Some codes require one smoke detector for every 1,200 square feet.