Venting of 90% furnace

[t527ed]

bottom drawing is the way lennox requires it in their instructions. also if venting is in unconditioned space exhaust must be insulated. drain pipes must also be heated and insulated.

[berad]

Originally posted by t527ed
bottom drawing is the way lennox requires it in their instructions. also if venting is in unconditioned space exhaust must be insulated. drain pipes must also be heated and insulated.

Trane says ditto in much of their literature. They want the reducers on a verticle. Although they show it other ways on their horizontal 90 plus drawings. My belief is to put them on a verticle to prevent trapping.

[docholiday]

I suppose even in reality, if the bottom of that 3: pipe were full of water, the volume of space above it would still be greater with the 3" pipe.

Plastic pipe is a very good insulation in and of itself. I have seen PVC Chiller pipes carrying 15 degree (F) water/gloycol that doesnt even show condensation on the outside. If on the other hand the vent is in an unconditioned space you would want to insulate it. Remember at freezing temps, the furnace will be running often.

[mark johnson]

OK, sounds like a unanimous preference for the alternate approach - thanks for the responses! I'll ask the contractor to redo it that way, he was very good at accommodating my wants.

I agree that the amount of water that would be trapped in the original approach would be small, and the opening would still be larger than a 2" pipe, but I just didn't like the thought of that water sitting there and festering. So if there are no concerns with keeping the vent all 2" through the first 90, that's what I'll have the contractor do.

I also failed to mention that this home is in San Diego, so we don't have to worry about freezing temperatures here.

Thanks for all your help!

[johnl45]

The contractor did a good job you don’t have a problem.