How To Look At A House
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Why is it dangerous to run an exhaust duct for a gas clothes dryer through an air conditioning return air plenum?
Thursday, June 14, 2018
Most gas appliances exhaust the combustion gases they create through a flue to the exterior, but a gas dryer pumps both the hot/moist air created by drying the clothes and the combustion gases through the dryer exhaust vent. Gas dryers create plenty of water vapor and carbon dioxide during combustion, which is added to the water vapor generated by the drying clothes. Any leakage of vent piping unloads moisture and carbon dioxide into the air flow of a home’s HVAC system. Even worse, if the burners are malfunctioning they produce deadly carbon monoxide.
We came across this situation in a vacant home we inspected today. The photo above shows one side of the plenum below the furnace/air handler where the dryer duct enters it. Mold surrounding the dryer exhaust duct appears to be due to leakage of hot/moist air at the connection between the flexible dryer vent connector and the metal duct that runs to the exterior.
Although running a dryer duct for an electric clothes dryer through a plenum is also not a good idea, because you are effectively installing a heating device in the air intake to the system, a gas dryer vent through a plenum is actually dangerous.
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To learn more about heating and air conditioning systems, see these other blog posts:
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