Height of Furnace Flue

Would you recommend this flue be raised??

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.

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.:slight_smile:

Almost pom pom like.

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

I know. hahahahaahaha

How far from the vents was the flue?

Looks ok.

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

Thanks!! Approx. 12 inches.


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

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.

Are those tables in the current IRC?

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

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

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



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

Looks like a very good general information on B vents.

The diagram explains the general height rule very well.

Thanks Larry! Bing found this useful thread.:wink:

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?

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