condensate traps

Are they required? I’ve read that if the line drains into a plumbing stack then vents are required but if they are just run to the outside of the home to drain on the ground then they are not required. Just trying to clarify cause I’ve seen homes with and without them and the pipes just run to the outside of the home with gravity drainage. Thanks.

Condensate traps should be installed on all systems, In my opinion.

They keep conditioned air in and unconditioned air out.

In the case of a unit with a negative pressure evaporator (up flow or where the blower is up stream of the coil), failure to have a trap may cause the condensate to overflow the coil drain pan and flood the inside of the unit.

Also, if you have a positive pressure evap coil, discharging air outdoors through the drain will require the same amount of unconditioned air to be drawn in from door and window openings. May draw in Radon, mold ect… from basements/crawlspaces. Is an efficiency concern and a potential health risk if contaminates are or could be present in the future.

Condensate drain lines should never empty into a plumbing vent stack. Sewer gases could back up into the air-conditioning system and spread through the house.

This is basically very true but never say never as in this area AHJ allows condensate to drain into a vent stack if the furnace is a 90% high efficiency which would make the trap a continuous flow trap. That is the only exception.

Thanks Chris, Good catch, I meant to address that issue.

If the condensate drain is installed to a sewerage system, the sewerage system must be trapped (a wet trap if necessary) not just the condensate drain. Unless the equipment is a high efficiency furnace that produces condensate in both heating and cooling modes, the trap will dry out and sewer gases are likely to be drawn into the HVAC system and distributed throughout the house during the off-season.

and, thank you Charlie B!

There you go posting when I’m thinking! :slight_smile: I was just thinking about “never say never”.

note AC trap and vent configuration and sink tail pipe Y location
attic istalled units should have condensate drain line insulated

I find these vent pipes in the wrong location all the time. Either not used in connection with a trap or on the wrong side of the trap (causing a conditioned air leak and associated issues).

Are you referring to when you feel air blowing out of the vent pipe?

Yup, blowing or sucking.

so the vent should be on the “downside” of the vent not closer to the unit, correct?

Some units have the condensate drain stub on the blower’s suction side of the evaporator and will draw the condensate water backwards up the pipe if there is no trap.
When the drain stub is on the pressure side there is no need for a trap because even IF it is connected to the building drain it should be an indirect connection with a proper air gap.

At least that is how it is around my part of the country but almost all condensate drains around here go to a basement floor drain or in the case of attic units to the yard outside.

Kind of like always, you’re never always right. Thanks for updating me. :stuck_out_tongue: