Building cavities that are framed with wood studs and drywall for the purpose of creating a shaft running up to the attic that connects to a return air duct are not as popular as they were years ago, and for good reason: they leak and are difficult to maintain. Also, condensation can on the uninsulated surfaces can be a problem.

    The current building code allows them only for return air (not supply air) and they cannot convey air from one floor to another. The photo above was taken looking up into a stud-framed cavity to a duct connection at the attic level of a 1980s house. Yes, the cobwebs are real and so are the seams and gaps in the drywall in the floor of this cavity shown below, with dust/dirt accumulation from the suction of unfiltered air from adjacent spaces around the unsealed base plates.

    Because the air filter is usually placed just behind the return air register at the bottom of the cavity, everything that gets pulled through the tiny openings in the shaft ends up stuck to the evaporator coils in the air handler. This configuration is approved by the building code, so we don’t recommend repair, but it a less than ideal component of an HVAC system.

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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 find out the age of my air conditioner or furnace?

• 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?

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

• How can I find out the age of my air conditioner or furnace? 

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