Can I replace a portion of a furnace exhaust pipe by using two couplings?

I live in York Region (Vaughan Ontario). The gas company came by and performed a visual inspection. They identified my furnace exhaust pipe (black APS 2") is starting to crack at the coupling (its about 2 feet above the actual furnace) and said I should replace the pipe with the white PVC (Ipex or Royal).

I did some research and based on the recommendation, I should prime, then glue the new pipe.

I’m assuming I can cut the black pipe with enough room to add a coupling just above where the pipe comes out of the furnace and then continue with the new white pipe.

Can I also add a coupling at the other end near the exterior wall of the house? Do I have to replace the full length to the white pipe to make it go outdoors? Obviously its easier to just add a coupling near the wall since the exterior is all caulked and already sealed. In essence I would have about 2 inches of black pipe coming out of the furnace, then about 8 feet of white pipe, another coupling joined to about 1 foot of black pipe which is already going out doors.


Home Improvement Asked by domdc1 on December 29, 2020

3 Answers

3 Answers

No, you can't do this

Since you're in Canada, your special gas vents (used for condensing appliances) fall under ULC-S636, and must be installed according to their accompanying listing instructions as a result, which strictly prohibit the mixing of vent systems from different manufacturers. So, you'll have to rip all the old ABS out and put in a new vent system outright. (While you could use ULC-S636 listed PVC or CPVC if it's available to you, the general recommendation would be to use something higher-temperature-rated, such as a high-temp polypropylene at a minimum or better yet stainless steel venting, as the margins on PVC especially are quite slim when used in venting applications.)

Answered by ThreePhaseEel on December 29, 2020

There is a special glue that will work on both pvc and abs I found it a few years back for making transitions this would allow you to use a coupler like you want. I think it was called abs to pvc glue made for transitions.

Answered by Ed Beal on December 29, 2020

You need to look at the markings on the white pipe. Standard DWV PVC should not be used for flue gases, but unfortunately it is used all the time. If the entire run is not rated for flue gases, then you should replace it.

Answered by longneck on December 29, 2020

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