Missing P-Trap on HVAC Condensate Drain

HVAC systems are complex in nature, and it is important to have a trained Professional Inspector inspect your HVAC system who can find deficiencies that an untrained eye would not notice.

One problem that I often see is a missing P-Trap in the condensate drain.  There are many reasons why the P-Trap would be missing, but the most common is that the installation was completed or modified by the homeowner.

The image above shows a condensate drain line that is missing a P-Trap

What is a P-Trap?  A P-Trap is a trap is a device which has a shape that uses a bending path to capture water to prevent sewer gases from entering buildings, while allowing waste to pass through.  Without a P-Trap, gases from the sewer line to which it is connected will make their way up through the drain, causing the sewer smell to enter the dwelling.  The condensate drain P-Trap should be equipped with a cleanout downstream nearby with a removable cap.  The exit point of the P-Trap should be lower than the entrance point to allow the condensate to properly drain.  For information on routing your HVAC Condensate drain line, check out  this article on HVAC Condensation Drain Line Routing

hvac ptrap

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HVAC Condensation Drain Line Routing

During a Professional Home Inspection performed by Blue Star Real Estate Inspections, one of the items checked is the HVAC condensate drain.  Your HVAC System can produce up to 80 gallons of condensate per day.  Condensation is produced by your HVAC system as it removes humidity from the air as it is conditioned.  The best place for this condensation to go is the city sewer system.  PVC piping is the most common material, but cast iron, galvanized steel, copper, polybutylene, polyethylene, ABS, and CPVC piping can also be used.  Whichever piping material is used, it should be no less than 3/4″ Nominal Pipe Size, and should not change size throughout the length of the pipe.  The piping should be sloped to allow gravity to drain the condensate from the pipe, unless a condensate pump is used.

The discharge location should ideally be tied into an existing bathroom or kitchen drain.  Condensate should never drain into any vent stack.  The illustration below shows acceptable condensate drain tie in locations.

Acceptable condensate drain locations

On one home inspection that I performed, I came across a condensate drain line that discharged onto the ground directly outside the wall.  The condensate pooled up at the foundation of the house.  While keeping your foundation moist is a good idea, you do not want isolated water pools at any time.  Serious foundation damage could occur.

Picture shows condensate drain discharging to the exterior of the house and pooling water

The property in question above was on a septic system rather than city sewer.  Routing condensate lines to the septic tank is acceptable.  More than likely the owner wanted to avoid excessive septic cleaning/pumping.