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Old 04-03-2006, 08:38 AM  
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Default High efficiency furnace chimney liner

Hi all,
sister selling house and inspection showed she needs a chimney liner for her furnace.
It was swapped out a few years ago, and is apparently a high efficiency model, and the liner was not installed.
I will be doing the install, and am curious of a few things.
Is there a particular brand or material that is recommended?
Do I attach lengths of pipe for vertical rise with screws, or foil tape, both?
What diameter pipe, 3" or 4"?
Thanks in advance.

I thought i had it figured out, but after checking at local home supply store, am a bit confused.
All they stock is the 'B', double walled, 3" or 4" ducting, that i assumed was for venting gas appliances w/out a chimney.
Do you need to use this 'B' ducting inside of a chimney also?
I intend to connect the water heater and the furnace together with a Y, before going through the basement wall into the chimney.
Is it alright to use standard galvanized ducting before entering the chimney?
They don't seem to have 'B' rated Y's that have a 3"(WH) and 4"(Furnace) inlet, and a 4" outlet.

Last edited by Ducttapeman; 04-04-2006 at 01:13 PM.
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Old 04-07-2006, 07:31 AM  
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Long story short, the house was sold as is.
She dropped the price a bit to make it work, which I thought was a mistake, but oh well.
The actual furnace is not a high efficiency model, but does have the AFUE rating of 80%, which I guess makes it a candidate for the chimney liner.
Some handy man visited her and said any furnaces of 80% or higher efficiency needed a chimney liner, if vented into one.
I don't know all the codes myself, but it seems that any furnace should require a chimney liner, since I doubt any are made any longer that are not as efficient as that.

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Old 04-07-2006, 09:47 AM  
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As far as I know, chimney liners are used when the chimney flue joints are leaking or could leak with lower efficiency furnaces. Most High efficiency furnaces >95% need to be ducted directly thru a wall. The exhaust gases from a high efficiency furnace aren't hot enough to duct up a chimney because by the time it gets to the top, it will have cooled and condensed.
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Old 04-15-2006, 10:34 PM  
Join Date: Feb 2006
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what you need to do is call the local building inspector at your local city hall.

building codes vary from city to city, so what is code in one town, might not be code in another.

Here in chicago, installing 80% efficient furnaces in an existing chimney is fine in a remodel or exhisting home.(granted that the chimney is in good shape and doesn't leak.)

if in new consruction, it is necessary to run a flue pipe. which exists of the b-vent rated double wall sections of pipe. the size of the pipe would depend on the amount of btu's that you are exhausting flue gas from and the distance of the run from the appliances to the roof termination. national code requires that there be a 1" clearence from the flue pipe to ANY combustable materials.

in chicago, we terminate the b-vent into the utility room where the appliances are located, then run a single wall tee and single wall pipe from our appliances to the flue. (your local code might require all b-vent)

90% efficient furnaces is a whole different story.

the only way to be sure that everything is up to code. and to get your answers without question in your area is to call the local building department and ask for the city inspector. Home inspectors will not give you the info necessary for a proper installation.

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