Thread: Venting gas furnace in attic

I need to vent a gas furnace 83% non condensing through pitched roof. Furnace connection is 4" dia with draft inducer motor. Furnace is located in attic with connection 30" below and 18" offset from roof peak. A) Must I use B vent? B) How high should the penetration through roof be" C) Is B vent rain cap suitable? Appreciate any input. Thank You Brian

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Brian
I can appreciate your wanting to do somethings yourself, however gas appliances should not be one of them.
Unless you KNOW what you are doing, please, get a professional in there to do the job.
Some things are just not DIY, this seems to be one.

Originally Posted by Brian Egan

I need to vent a gas furnace 83% non condensing through pitched roof. Furnace connection is 4" dia with draft inducer motor. Furnace is located in attic with connection 30" below and 18" offset from roof peak. A) Must I use B vent? B) How high should the penetration through roof be" C) Is B vent rain cap suitable? Appreciate any input. Thank You Brian

Hi Brian,

A B-vent is required in unconditioned spaces, which would include attics.

The best bet is to follow the manufacturer's installation instructions. Below is a link to DuraVent's site. There are a number of vent brands, so use the installation instructions specific to the brand you are using.

DuraVent

NC Code

503.5.4 Chimney termination.

Chimneys for residential-
type or low-heat appliances shall extend at least 3 feet I

(914 mm) above the highest point where they pass through a
roof of a building and at least 2 feet (610 mm) higher than
any portion of a building within a horizontal distance of 10
feet (3048 mm) (see Figure 503.5.4). Chimneys for
medium-heat appliances shall extend at least 10 feet (3048

I

mm) higher than any portion of any building within 25 feet
(7620 mm). Chimneys shall extend at least 5 feet (1524 mm)
above the highest connected appliance draft hood outlet or

I

flue collar. Decorative shrouds shall not be installed at the
termination of factory-built chimneys except where such
shrouds are listed and labeled for use with the specific factory-
built chimney system and are installed in accordance

with the manufacturer's installation instructions.