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Q. My client’s metal fireplace is supplied by a makeup air system with a built-in circulation fan. This fan — which plugs into an accessible outlet — is triggered by a heat sensor in the fireplace. While effective, it’s also very loud. To reduce the noise, I’d like to replace the fan’s on/off switch with a variable-speed control. Is that possible? The manufacturer doesn’t seem to offer anything.

A.Rex Cauldwell, a master electrician in Rocky Mount, Va., responds: Noisy single-speed fireplace fans are common. To reduce the fan’s speed — which can help solve the problem — I use a Dial-A-Temp control (866/667-8454, northlineexpress .com). This device (see photo, below) plugs into a 120-volt receptacle; the fireplace fan, in turn, plugs into it. Rated for motor loads up to 3 amps and 300 watts, it has both an on/off switch and a variable-speed switch. It costs about $20.

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Remember that you can’t use a light dimmer on a fan motor. Dimmers are designed for resistive devices — like the filament of a light bulb — and operate by lowering the voltage to the lamp. A fan motor is a capacitive and inductive device that needs a relatively constant voltage to keep it from overheating and burning out. A motor speed controller like the Dial-A-Temp contains electronics designed to create variable resistance while maintaining the constant voltage required by the fan motor.