What’s Wrong With My Furnace?

When heat comes on, lights go dim

by Paul Bianchina

HandymanQ: We recently moved into a home with electric forced-air heat. In the winter, every time the furnace kicks on, the lights in the house dim for a nanosecond. Is this something that can be addressed or fixed?

Before we moved in we had to replace the electrical panel (it was made by a company that went out of business years ago because their panels were known to start fires), and I’m wondering if there is something associated with that we can correct. Any help before furnace season starts is greatly appreciated! –Lea

A: The dimming of the lights is caused by a voltage drop that occurs during the startup phase of the furnace. When your thermostat calls for heat, the electric elements in the furnace begin to heat up before the furnace motor kicks on, a process called “heat anticipation.” It’s set up that way so that the furnace fan doesn’t blow cold air through the ducts before the furnace itself heats up. So when you hear the furnace kick on, that’s actually the sound of the fan motor starting up and activating the fan itself.

A couple of possible problems come to mind: The wires leading to the furnace may be too small, or you may have a loose or corroded connection. There should be two circuit breakers on the furnace itself, and they may be loose or faulty. It’s also possible that the furnace motor is going bad, or that you have some problems with the fan, the belts, or other internal furnace parts that are requiring an excessive amount of electricity in order to get turning.

Given the fact that the panel was replaced recently, you definitely want to have an electrician come out to inspect everything — the new panel, the circuit breakers, wire sizes, connections (including the connection to the utility company wires), grounding, etc. All this should be covered under the one-year warranty from the electrical contractor who did the work. I would also strongly recommend that you have the furnace checked and serviced by a heating company that deals with your particular brand of furnace.

One other thing: Since the electrical panel was replaced recently, your local building department will have a record of the permit. I would suggest that you obtain a copy of that, and make sure that the installation was inspected and approved and that the inspector didn’t note any problems.

Remodeling and repair questions? E-mail Paul at [email protected].
Copyright 2009 Inman News

See Paul Bianchina’s feature Security Door an Easy Update.
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