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-   -   Gas furnace venting Qs (non high eff) (http://www.diychatroom.com/f17/gas-furnace-venting-qs-non-high-eff-88213/)

WallyWoggle 11-30-2010 04:27 PM

Gas furnace venting Qs (non high eff)
 
Hello all! :)

I was hoping someone could help me with a couple of questions about gas furnace venting. I have a gas furnace in the attic with a short run (3' maybe) of metal venting to the roof.

The current venting is in bad shape so I need to redo it. It has 4" double-walled aluminum, a single walled bend (!) and then double-walled to the roof vent outside.

There is no sealing anywhere - pieces are just dry fitted together.

Q1) do I need to seal the venting to the flue collar (?) on the furnace or is it OK to dry fit.

Q2) do I need to seal each segment of venting?

Q3) My understanding is that the double-walled venting needs to be 1" from anything combustible. What's the best way to ensure that this requirement is met - particularly at the roof?

Thank you!!

Marty S. 11-30-2010 04:47 PM

Double wall locks together with a slight turn of the pipe so no sealing required. Should be a screw in each joint and 3 screws to hold it on the flue collar. To get clearance it's best with 2 people. One in the attic watching the clearance and the other setting the pipe pumb and level. The roof person will trim wood as needed.

WallyWoggle 11-30-2010 05:25 PM

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Quote:

Originally Posted by Marty S. (Post 543170)
Double wall locks together with a slight turn of the pipe so no sealing required. Should be a screw in each joint and 3 screws to hold it on the flue collar. To get clearance it's best with 2 people. One in the attic watching the clearance and the other setting the pipe pumb and level. The roof person will trim wood as needed.

Thanks Marty. I see now how the double wall pipes lock together.

I attached a pic of the flue collar... it's basically just a hard plastic piece with no screw holes. The outer part of the double-walled vent pipe slides over it and the inner part "catches" on it. Is this a good enough seal?

thx

Marty S. 11-30-2010 05:53 PM

The inner liner should also go over that. If not a short piece(less then 5" long) of single wall can be used as a starter. Use self tapping screws on the collar or predrill, they break easy.

kelipop 11-30-2010 06:22 PM

They make metal connectors to replace the plastic one.

WallyWoggle 12-09-2010 11:36 AM

The saga continues...

Thanks to the advice of folks here and a lot of Googling I was able to put together a decent vent pipe. I had to build a pipe from the furnace to the old chimney and cap which was a bit tricky.

Once everything was in place I noticed that the roof penetration for the chimney has roofing paper and shingles that were not particularly well trimmed... they are crowding into the 1" gap around the pipe. Is this something I should be concerned about? Any recommendations out there on how/what tool to use to trim it up if needed?

Marty S. 12-09-2010 06:41 PM

Use a knife and cut away. Us HVAC guys will get denied on inspection if there's not the correct clearance. Roofers on the other hand don't get inspections here and I've seen a lot of flues touching wood after a reroof and the places didn't burn down.


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