How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

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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:

How can I find out the SEER of my air conditioner? 

My air conditioner won't turn on. What's wrong? 

How can I find out the size of my air conditioner? 

How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

Where is the air filter for my central air conditioner and furnace? I can’t find it? 

Does an old air conditioner use more electricity as it ages? 

How did homes stay cool in Florida before air conditioning? 

What is wrong with an air conditioner when the air flow out of the vents is low?

Why has the thermostat screen gone blank? 

Why does it take so long to cool a house when an air conditioner has been off for a while? 

Why is my air conditioner not cooling enough? 

What are the most common problems with wall/window air conditioners?  

Will closing doors reduce my heating and cooling costs? 

    Visit our APPLIANCES and HEATING AND AIR CONDITIONING pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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