Tech Tips

Inspecting Heating / Cooling Ducts


We see different sizes and configurations of heating / cooling ducts. In addition to ensuring the ducts are properly sealed, there are many other issues associated with ducts. On a forced air furnace, home inspectors should ensure return ducts are properly sealed. Duct tape is not recommended. Mastic or foil tape is recommended. Not only will this ensure that the system is efficient, open return ducts may be dangerous. Flue gasses from the furnace or other fuel burning appliances in the area can be drawn into the system causing Carbon Monoxide to be distributed to the living space. Also contaminants can be drawn in like mold, dust, and fungus.  All seams should be sealed. Ducts should be as straight as possible. Direction changes will reduce flow and efficiency. Sheet metal secured and properly sealed to floor joists and wall studs can be used for return air only. Here are some other guidelines a home inspector can use when inspecting ducts:


  • Ducts should be supported on the framing
  • Sheet metal ducts should be supported with at least ½ inch wide straps at less than 10 feet intervals
  • Flex duct should be supported by at least 1 ½ inch straps at less than 4 feet intervals
  • Plastic zip ties should be used to secure flexible duct
  • The use of flexible duct should be limited unless the HVAC system has been properly sized and evaluated by a qualified contractor
  • Ducts should be supported within 1 foot or 1 duct diameter (use the smaller of the two) at all bends and fittings
  • Plenums should be supported independently of the distribution ducts
  • Ducts should be connected with self tapping screws or rivets

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