Condensate drain in the crawlspace air gap with P-trap however

Inspection today found that the condensate line from the AC evaporator was emptying into a waste pipe with a P-trap, in the crawlspace. Are there any standards or requirements on the height that an open drain such as this would need to be? My thinking is any kind of drain blockage downstream is going to allow sewage to back up into the crawlspace without anyone knowing since this drain is much lower than a drain such as at the bathtubs (where you normally get your first clue of sewer line blockage). Any standards or requirements as to the height of an open drain such as this or is it even allowed below floor level or in an area that cannot be seen if a problem. I know that there are standards and requirements for the height above the P-trap for a washing machine but is this particular set up addressed anywhere?


Good find, Larry.
I think I would be recommending a backflow preventer for that exact potential occurence and also a trap primer to make sure that trap doesn’t dry out. JMHO


Unless the heating side of that HVAC unit is a condensing furnace, the trap is going to dry during the winter and you’ll get sewer gas into the house through the condensate drain. I second the recommendation for a trap primer installation. Also, what you have right now is an air break not an air gap and it really should have an air gap.

Here is IPC for air gap:

Here is the UPC:

basically 1 inch minimum for upc and not less than 2x the diameter of the indirect waste pipe opening for IPC


On the surface this appears to be the exact configuration that we see all the time in a basement where the condensate drain discharges into a floor drain. The primary difference is that in the basement example there is a chance that the occupants would see a sewer backup however in this crawlspace that probably wouldn’t happen. In these instances we usually see a condensate pump with the discharge directed up and out to daylight. I think I would call out the plumbing drain for it’s potential problem and the condensate system for needing a pump or other discharge method.


Thank you for all the responses. I appreciate it! In my area contractors (especially sub contactors) just do not know how to deal with crawl space applications. Almost all homes are slab on grade except for those on expansive soils. So, when I do an inspect a home with a crawlspace I find several issues. this one was no exception… however this one did come equipped with a very dead, maggot infested and stinking squirrel carcass…lots of newly hatched flies also taking wing…luckily their numbers were kept in check by the dozen or so Black Widow Spiders that kept me company while I traversed the very damp crawlspace…


Hope you did not bring one home.

My wife say’s no new Pests…or was it pets?