Checking Furnaces for Carbon Monoxide

By Barry Stone

Dear Barry,

We're buying a 12-year-old home, and there is a difference of opinion between our home inspector and a heating contractor. Our inspector checked the forced air furnace for carbon monoxide. He inserted a probe into the flue pipe and said the meter went off the scale. In his opinion, the furnace is unsafe. The sellers called a heating contractor who found no carbon monoxide problem at all. We don't want to go ahead with the purchase until we know for sure that the heater is safe. Who should we believe and what should we do? --Slade

Dear Slade,

The place to check for carbon monoxide (CO) is not inside the flue pipe. In fact, the only reason to insert a probe into the flue would be to check the CO test device to make sure that it is working properly. Any furnace is likely to have some CO in its exhaust system, since all furnaces produce CO as a byproduct of combustion. The fact that this was detected in the flue is neither surprising nor a basis for concern. As long as no carbon monoxide is being emitted into the dwelling, and as long as there are no visible defects in the heat exchanger, there is no apparent need for concern.

The proper locations to test for carbon monoxide are the warm air heat registers and areas near and around the furnace and flue pipe. For a reliable third opinion, have the heating system checked by the local gas company.

Copyright 2003-2006 Barry Stone. Distributed by Inman News Features.