Garge Furnace Venting


Old 10-31-17, 11:28 AM
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Garge Furnace Venting

I have a gas forced air furnace (not high efficiency) in my detached garage. The previous property owner vented this furnace through the wall with 6" round single-wall metal ducting, with a 90 and only 2 feet of vertical run. The pipe is only about 12 inches from the outside wall and about 12 feet from the roof. I can see where the furnace exhaust had begun to melt the vinyl siding on the garage.

I would like to correct this issue and run the exhaust up above the roof line. What type of stove-pipe would be appropriate (double wall)? Is there a standard for distance from the outside wall and distance to extend above the roof line?


Last edited by psustang89; 10-31-17 at 11:47 AM.
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Old 10-31-17, 01:00 PM
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This information is usually found in the installation manual of your furnace.

Usually type B double wall vent pipe.

Take a look at page 8 of this manual...
Old 11-01-17, 04:35 AM
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Unfortunately, the furnace in question is very old and was installed by the previous owners - I do not have a manual.

Can a gas furnace be vented horizontally, without a vertical run, using a cap like that in the link below?
Old 11-01-17, 09:55 AM
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Try posting the model number. We may be able to find a manual.

On a gravity exhausted furnace (without draft inducer) the flue line needs to go above the roof line. You are also limited to any type of horizontal run. The line from the furnace to the vertical flue must always be pitched upwards.

I believe that cap you linked to is not for a furnace like yours. It looks to be for draft induced furnaces.

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