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Old 07-16-2020, 07:40 AM   #1
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Furnace Flue HELP


The last few feet of furnace flue was damaged during a roof replacement. I am trying to figure out exactly what this vent is so I cant attach to new section to penetrate the roof and connect to a faux chimney.
Any help on the best way to vent this thru the roof is greatly appreciated.

Would it be ok to slide a 7 inch round duct into the existing flue (existing flue inside diameter is 7 Inch, 7 inch round fits snug) and vent through the roof into faux chimney? See attached photo.
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Old 07-16-2020, 09:21 AM   #2
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Re: Furnace Flue HELP


No! You would not be doing yourself or your family any favors. Take a look at the other end of the flue (basement?) sometimes the manufacturer info is embossed on the female end of the pipe. It looks pretty old, not sure you could find a replacement piece anyway. Did you do the roofing work yourself or have a contractor do it? If you used a contractor it's a good time to involve their insurance company. Don't do any hack work on the flue or accept any from others.
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Old 07-16-2020, 09:29 AM   #3
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Re: Furnace Flue HELP


I cannot find any literature on the pipe and yes it it looks very old.
I did the roofing myself and just to make sure there arnt any issues with fumes and what not.
Looking for a proper DIY method that is cost effective.
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Old 07-16-2020, 12:49 PM   #4
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Re: Furnace Flue HELP


That looks like what we call a B Vent which is a pipe within a pipe and has a air gap inside.

Most of the time you cannot match pieces to old chimneys because the pieces are obsolete. You may have to run a new one from the basement up thru the roof.

Google : B vent chimney and there is lots of info there for you. If it is for a oil furnace you may have to use a A vent as B vent is only for gas.

Google: A vent chimney for that info.
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Old 07-16-2020, 01:50 PM   #5
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Re: Furnace Flue HELP


It can be better to just put a new high efficiency side-wall vented furnace than invest in a new b-vent system.

To justify it, the furnace better be 80% and not natural draft, less than 15 years old. There's no point of throwing good money after bad.
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Old 07-16-2020, 02:17 PM   #6
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Re: Furnace Flue HELP


Is there not a safe way to connect to the existing pipe in the picture without paying a ton of money?

The pipe is about 12" below the roof.
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Old 07-16-2020, 02:54 PM   #7
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Re: Furnace Flue HELP


I would not adapt new pipe to an old b-vent unless approved to work with the same venting system.

If your house is only one story with the furnace in a closet, basement or crawlspace putting in a new b-vent may not be that bad, but still not worth it when you have an old furnace.
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Old 07-16-2020, 04:47 PM   #8
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Re: Furnace Flue HELP


Quote:
Originally Posted by BigRick15 View Post
Is there not a safe way to connect to the existing pipe in the picture without paying a ton of money?

The pipe is about 12" below the roof.
No.

If anything happened and you had a fire your insurance company may void you. You cannot legally sell a house with a unsafe chimney either. You could be liable down the road if someone gets sick.
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Old 07-16-2020, 08:34 PM   #9
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Re: Furnace Flue HELP


How much damage occurred on the piece of vent in question? Pic would help.
Does your water heater vent up the same pipe?
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