Height of Furnace Flue

bhartley · February 4, 2009, 12:21am

Would you recommend this flue be raised??

lkage · February 4, 2009, 12:40am

Here’s a guide:

Table of Type B-Vent Rooftop Clearance Requirements

The 1992 Vent Sizing Tables require that all Type B gas vents terminate above the roof with a listed cap or listed roof assembly in accordance with the manufacturer’s instructions.
Vent caps 12" and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as follows:
ROOF PITCH - rise/run in inchesMINIMUM HEIGHT*
Flat to 7/12 - 1.0 foot above the roof surface
7/12 to 8/12 - 1.5 feet above the roof surface
8/12 to 9/12 - 2.0 feet above the roof surface
9/12 to 10/12 - 2.5 feet above the roof surface
10/12 to 11/12 - 3.25 feet above the roof surface
11/12 to 12/12 - 4.0 feet above the roof surface

Continues to 21/12 pitch at 8.0 feet

Vent caps larger than 12" must be located at least 2 feet above the highest point and 2 feet higher than any portion of the building within a horizontal distance of 10 feet.

From: http://www.inspect-ny.com/chimneys/B-Vent_Chimneys.htm

bhartley · February 4, 2009, 1:09am

Thanks!! Larry.

belliott · February 4, 2009, 1:26am

I am more concerned about the giant shadow of a robot I see in the picture,which is castings itself on to the roof image.

It appears to have a strange dome or bulb like contraption sticking from its head.

Almost pom pom like.

bhartley · February 4, 2009, 3:26am

That is my stocking cap 25 degrees at 4 PM!!

belliott · February 4, 2009, 3:29am

I know. hahahahaahaha

How far from the vents was the flue?

Looks ok.

We had this issue last month. (caused a debate)

bhartley · February 4, 2009, 3:42am

Thanks!! Approx. 12 inches.

belliott · February 4, 2009, 4:02am

](http://inspect-ny.com/chimneys/Chimney_Height.htm)

kshepard · February 4, 2009, 4:07am

lkage:

Here’s a guide:

Table of Type B-Vent Rooftop Clearance Requirements

The 1992 Vent Sizing Tables require that all Type B gas vents terminate above the roof with a listed cap or listed roof assembly in accordance with the manufacturer’s instructions.
Vent caps 12" and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as follows:
ROOF PITCH - rise/run in inchesMINIMUM HEIGHT*
Flat to 7/12 - 1.0 foot above the roof surface
7/12 to 8/12 - 1.5 feet above the roof surface
8/12 to 9/12 - 2.0 feet above the roof surface
9/12 to 10/12 - 2.5 feet above the roof surface
10/12 to 11/12 - 3.25 feet above the roof surface
11/12 to 12/12 - 4.0 feet above the roof surface

Continues to 21/12 pitch at 8.0 feet

Vent caps larger than 12" must be located at least 2 feet above the highest point and 2 feet higher than any portion of the building within a horizontal distance of 10 feet.

From: http://www.inspect-ny.com/chimneys/B-Vent_Chimneys.htm

Darn-o! I thought the 2/10 termination rule applied to all combustion vents for adequate draft reasons.

belliott · February 4, 2009, 4:11am

Yeah, thats what I used to think.
I am still not 100 percent sure about if it should be 12 inch above that ridge in the picture.

Just looking at it makes you see down draft potential.

kshepard · February 4, 2009, 4:14am

Are those tables in the current IRC?

belliott · February 4, 2009, 4:18am

Good question.
I notice that you should check local codes and manufacturer guides.

belliott · February 4, 2009, 4:23am

You know what?
Go here and download, the first PDF guys.

This is the best info on the subject and answers it.

http://www.hartandcooley.com/faq-bvent.htm

http://www.hartandcooley.com/vent/sizing%20guides/Gas%20vent,%20chimney%20sizing%20&%20application%20guide.pdf

kshepard · February 4, 2009, 4:28am

But if that’s Hart & Cooley’s guide, they’re just one manufacturer. Might their information not apply everywhere?

belliott · February 4, 2009, 4:46am

Looks like a very good general information on B vents.

The diagram explains the general height rule very well.

sfetty · May 8, 2016, 5:10pm

lkage:

Here’s a guide:

Table of Type B-Vent Rooftop Clearance Requirements

The 1992 Vent Sizing Tables require that all Type B gas vents terminate above the roof with a listed cap or listed roof assembly in accordance with the manufacturer’s instructions.
Vent caps 12" and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as follows:
ROOF PITCH - rise/run in inchesMINIMUM HEIGHT*
Flat to 7/12 - 1.0 foot above the roof surface
7/12 to 8/12 - 1.5 feet above the roof surface
8/12 to 9/12 - 2.0 feet above the roof surface
9/12 to 10/12 - 2.5 feet above the roof surface
10/12 to 11/12 - 3.25 feet above the roof surface
11/12 to 12/12 - 4.0 feet above the roof surface

Continues to 21/12 pitch at 8.0 feet

Vent caps larger than 12" must be located at least 2 feet above the highest point and 2 feet higher than any portion of the building within a horizontal distance of 10 feet.

From: http://www.inspect-ny.com/chimneys/B-Vent_Chimneys.htm

Thanks Larry! Bing found this useful thread.

jbernard · December 27, 2016, 2:58pm

New construction. This stack appears to be too short, but I want to double check before getting into a discussion with the builder. Roof is 7/12 pitch. The stack is 22 inches tall and 21 inches from the roof and does not extend above the roof peak. Thoughts?

ccurrins · December 27, 2016, 7:13pm

Flat to 7/12 - 1.0 foot **above the roof surface. ** No problem.