Tracking Down Knob-and-Tube Wiring

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Q: We live in an 1840s Greek Revival house that, among other challenges, has no insulation. We'd like to take advantage of our utility company's energy-efficiency incentive program, which would pay up to 50 percent of the cost of blowing cellulose insulation into walls and ceiling areas. However, the contractor doing the work needs verification from a licensed electrician that the house is free of knob-and-tube wiring before he can begin. Our electrician says that, short of opening up the walls, he can't certify that the house is completely free of this old wiring. What do we do?

— Robert and Sarah, Manchester, MA

A: Allen Gallant replies: Knob-and-tube wiring was used on many houses until about 1940. It works fine if it's in good condition, but if it's buried in insulation while still being used, it becomes a fire hazard.

After disconnecting the power, an electrician will check all circuit boxes, switches, receptacles, and light fixtures to look for live knob-and-tube circuits. If everything is Romex or armored BX cable, you're probably in good shape. It's quite possible that there are still runs of disconnected knob-and-tube wiring in the walls or ceiling cavities, even if the house has been completely rewired. But if they're disconnected, they're not a threat.

Believe me, this is not a job you can afford to mess up; turn it over to an experienced electrician who's worked on and knows his way around old houses.

(Electrical contractor Allen Gallant has wired many This Old House TV projects.)

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