Flue Vent Thru Roof

[Stephen G Sheldon]

What is the height requirement for a furnace flue vent exiting the roof?

[Matt Fellman]

Lots of factors including roof slope, nearby structures (dormers, etc.). The best thing is to find the manufacturer's specs.

There's a snapshot of the section in the Codecheck book that deals with is.

In general, I'm often surprised at how close they can be in many applications. Most of the time I'm suspicious I look it up and it's okay.

[Stephen G Sheldon]

Matt,

Thanks.:)

[A.D. Miller]

As MF stated there are many factors to consider: type of vent, type of appliance, distance from sidewalls, etc:

Try: http://www.duravent.com/docs/instruct/l950_nov99.pdf

or:

[Richard Pultar]

excess height is very common code violation.

[Scott Patterson]

excess height is very common code violation.

Why would a properly supported and constructed flue that is higher than the code requirement and meets the appliance manufacturers requirements be a problem or violation as you call it?

[Jerry Peck]

excess height is very common code violation.


Richard,

I'm wondering the same thing as Scott.

First, though, define "excess height" when only a "minimum" height is stated ... what would "excess height" be?

[Richard Pultar]

A B vent to a gas appliance must be sized properly to heat up rapidly to ensure a strong draft, and minimal condensation. Excessive vent exposed to cold outdoor temperatures is to be avoided.Since vent walls are supposed to heat up and dry out the condensation before the appliance cycles off.
Long connector runs in cold air spaces are also discouraged. Because of condensation and corrosion .
The sizing tables are clear that there are minimum and maximum BTU inputs. The Idea that bigger is better is not appropriate. here. This includes the overall length of the system.

[Jerry Peck]

The sizing tables are clear that there are minimum and maximum BTU inputs.

Richard,

I am aware of the sizing tables and the sizes and heights, however, the other sections of the code and the manufacturer's installation instructions specify "minimum" heights, not 'maximum' heights.

I also understand why the vents are not to be oversized, again, however, one must go by the manufacturer's requirements and the code, which specify "minimum" heights.

If a home inspector wants to get into this in more depth and start checking sizing of vents, then their work will become very in-depth and very time consuming - otherwise the code and manufacturers address (being repeated here) "minimum" heights - not "maximum" heights.

[Jack Murdock]

Stephen,
The 3 2 10 rule is easy to remember. The b-vent pipe must come at least 3 feet above the roof and be 2 feet higher than anything within 10 feet. This does not apply to direct vent appliances which must follow manufacturers instructions.

Jack

[Jerry Peck]

Stephen,
The 3 2 10 rule is easy to remember. The b-vent pipe must come at least 3 feet above the roof and be 2 feet higher than anything within 10 feet. This does not apply to direct vent appliances which must follow manufacturers instructions.

Jack,

That's for chimneys, not vents.

Vents is a more complicated:
1*, 2-8/10 rule I made
*the minimum height depends on the slope of the roof, the least allowed being 1 foot

It is not as easy of a rule to remember, or as simple to apply, as the 3, 2-10 rule for chimneys.

[Jack Murdock]

Jerry,
you are 100% correct. I apply 3/2/10 for everything....my bad.

Thanks

[Richard Pultar]

3 2 10 is for solid fuel burning CHIMNEYS,
VENTS as in B vents are vents they have the same minimum as a plumbing vent.
according to the Simpson Dura--Vent Sizing handbook .
Excess height is to be avoided IF you want to do the job code proper.

[Bob Harper]

Richard, I guess we're still missing what part of the code you are referring to with regards to max. stack heights. Sure, there is a functional limit but your injection of that word 'code' adds another dimension to it.

FYI, 3/2/10 is for ALL chimneys regardless of fuel.

There is a difference btw code requirements vs. good vent design and codes do not guarantee performance.

Bob

[Richard Pultar]

National Fuel Gas Code ANSI Z223.1 , NFPA 54, NFPA211, and the International Fuel Gas Code.
I am only addressing Category I gas appliances.
I find the use of flue and vent in the same term a oxymoron.