Question re combustion air connected to vent

Have a look at this picture of a high efficience horizontal furnace located in an attic. Is it common to use a Y tee and join the combustion intake vent with the exhaust vent with one single pipe exiting the residence?


No, Jamie. This is a violation. Supply and exhaust pipes cannot be combined and must be provided as two separate pipes. The air intake pipe should be at least 12" apart from the vent pipe for the furnaces up to 100,000BTU input.

Is that a canadian thing Yuri? Manufacturers, around here, have a pipe within a pipe where the furnace exhausts out the center and draws air through the outside pipe.

Well, I am in the Canadian thread, I just realized.

Thats a double wall pipe, there should be no problem with the current set up.

Yes Jamie,

Do a search for Concentric, Co-linerar, or Co-Axial to explain the details of what Larry and Raymond mentioned.

I know we don’t recite “violations”, but just which one were you referring to?

Hay, I like that hole strap they use. I have not seen that one down here!

If this is a coax, direct vent assembly, then I stand corrected. But from the picture it looks like a normal ABS pipe.

I would also check the manufactures installation instructions.

Mixing ABS and PVC fittings is not normally allowed for plumbing systems except with a special sovent and the approval of the AHJ.

Is this also true for Flue Venting Systems??

Its a concentric vent kit. Perfectly OK as long as installed per the furnace/vent manufacturer’s instructions.

Pipes still need to be insulated in attic to prevent condensation.

Dear fellow NACHI members,

Since taking control of user account “gilstrachan” in hope of reducing the verbal diarrhea of Raymond and Roy, I have been hoping that this lunacy would be reduced. That sadly has not been the case.

**Mysteryman has come up with a way for you express your opinion and participate.

Non-members cannot post polls but ALL can vote on others reputation so here is the plan.

Option 1-
If you think Raymond and Roy should continue as they have been vote gilstrachan’s reputation DOWN and Raymond and Roy’s UP

Option 2-
If you think Raymond and Roy should shut-up and get a life
vote gilstrachan’s
reputation UP and Raymond and Roy’s DOWN

Let’s see what the membership of NACHI really thinks of these two boys antics.

Go to the yellow star at the top of the post to give reputation points.

Speak up NACHI. This is your BB too.**