Thread: High Efficiency Flue Termination

Greetings! I've been a long time reader, but now with the new website, I have been forced out of the shadows...That being said, I came across this situation on Sunday afternoon and could not find any material to say that it is wrong nor right.

PVC flue for a high efficiency furnace terminating through the roof instead of a sidewall. I've never seen that before. I check the HVAC code check book as well as some online resources and the only information regarding this points back to the original manufacturers instructions. It's a Carrier unit manufactured in May of 2002

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Nothing wrong with it going through the roof as opposed to horizontally through a wall as far as I know. Very common in these parts, usually with a bend at the top to keep out rain, but not always.

Sean
The roof termination on most, if not all hight eff. furnaces allow both sidewall and roof terminations. Generaly when you see the roof termination it was installed when the house was being build, for they have open cavitys to run the pipe. The side wall venting is generally done on change out systems where the origional unit was a much lower eff. system. Hope this helps.

Thanks guys for your help. The major concern I had was the possibility of condensation collecting in the flue and with it being cold in these parts and possibly ice forming in the flue. Originally, I thought it was a plumbing vent which I know under most circumstances would be too tall.

Thanks again, I like this posting thing...I'm glad Brian forced me out of the inspection closet.

Originally Posted by Sean Bacon

Thanks guys for your help. The major concern I had was the possibility of condensation collecting in the flue and with it being cold in these parts and possibly ice forming in the flue. Originally, I thought it was a plumbing vent which I know under most circumstances would be too tall.

Thanks again, I like this posting thing...I'm glad Brian forced me out of the inspection closet.

As you are in an area with a good amount of snow and ice, I would recommend that they place an elbow on the end of the pipe so it is turned down. This will help to keep out snow, falling golf balls, etc.

Another thought is that PVC does not have any UV protection and after a few years that pipe will become brittle. Yes, it happens to even smaller vent stacks, its just that they are not as exposed. Spraying them with a protective paint will help to protect it and will also make it blend in better with the surrounding roof, that is if they use a paint to match the shingles!

What's that vent (exhaust?) just off to the left in the photo?

What kind of clearances are required between the exhaust from the high efficiency unit and a building opening?

Before you go recomending the placement of an elbow on the top of the vent make sure the manufacture of the furnace allows that as not all manufactures advise or approve this. The water and snow that may fall down the pipe but the amount that does go down woll be taken care of by the furnace condensate removal system. Jerry does have a good point on the distance between both vents may not be proper.

In response to Jerry's question, that is presently the flue for the water heater (past for both earlier furnace and water heater). I don't see anything in the code check book that relates to clearance distances between to exhaust flues, though.

The furnace discharge proximity to water heater vent is satisfactory.
As for PVC deterioration - never have seen it and many many soil stacks around here are PVC.

Not interested

I agree that an elbow is not needed on the exhaust. I would be more concerned that the unit has sufficient cumbustion air if it is located near a natural draft water heater.