Condensate Drains and Air Gaps - Why?

I’m having a little trouble understanding this concept from the text:

6.3.3 Condensate Drain Connections
Condensate drains from air conditioner coils, condensing furnaces, and heat-recovery ventilators should not drain directly into a DWV pipe. An indirect drain using an air gap should be installed. In some locations, the direct connection of a condensate drain line into a stack is not permitted, even with a trap. The potential danger is that sewer gases may enter the house through the condensate drain line. It is not a cross-connection problem, but it is unsafe and unhealthy.

If the “potential danger is that sewer gases may enter the house through the condensate drain line”, wouldn’t that also happen through the air gap? I understand the function of the trap is to stop the sewer gases from entering the building, but I don’t understand why directly connecting condensate lines is prohibited.

Is the rule in place to stop shoddy installs?

Is it because the connection to the DWV wouldn’t be trapped? But then there is this line:

the direct connection of a condensate drain line into a stack is not permitted, even with a trap.

No because the condensate drain is up stream of the P-trap it’s draining into. The sewer gas will be stopped on the other side of the trap.

There would be nothing to stop the sewer gas from entering the condensate line if it’s connected directly to the DWV system.

The Charge of the Light Brigade

“Theirs not to reason why,
Theirs but to do and die.” :rofl: :joy:

Thanks Martin,

Your explanation makes sense! This was one of those times where I understood the parts and pieces of the system, but just couldn’t visualize their installation arrangement.

condensate_air_gap

Any thoughts on why a direction connection with a trap would be prohibited?

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With a direct connection, even with a P-trap, sewage would be allowed to enter the inside of the air handler.

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unnamed
That makes sense.

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Some air handlers cause a negative air pressure in the condensate drain line.

Also any trap in a direct or indirect drain will dry out when condensate is not produced because the a/c does not run in the winter. That is why some areas do not allow any connection to the sewer vent.

There is a “Wet Trap” device that can be installed to keep a trap full. But installing one is costly, will freeze at an unconditioned location, and negates the reason your dumping in the sewer in the first place. “Cheap and Lazy”.

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David, your post makes a lot of sense! Thanks for the help!