# Thread: furnace vent height on roof

1. ## furnace vent height on roof

Guys

furnace vent stack on a roof here in snow country Colorado--it is only 12 inches above roof--shouldn't it be higher

thanks

CVF

2. ## Re: furnace vent height on roof

There is a minimum height (which that looks like it doesn't meet), and a snow load height so it is above a minimum snow load depth.

3. ## Re: furnace vent height on roof

Originally Posted by Jerry Peck
There is a minimum height (which that looks like it doesn't meet), and a snow load height so it is above a minimum snow load depth.

I know snow load and I know snow debth, but I don't know "snow load height or snow load debth". Would you define those terms please.

I was under the understanding that the stack should have been 24" above the ridge.

4. ## Re: furnace vent height on roof

Originally Posted by Garry Sorrells
I know snow load and I know snow debth, but I don't know "snow load height or snow load debth". Would you define those terms please.
I used those terms to help determine the depth of the snow.

From the 2015 IRC
- Figure R301.2(5) Ground Snow Load
- - Colorado shows "CS", which means that site-specific Case Studies are required
- - - however, the snow loads shown are 10, 15, 20, 30, 35, and CS.

If we make a presumption that CS likely indicates a snow load greater than CS (simply because the lesser snow loads are shown - and this could very well be a false presumption, but this is for explanation purposes only, so accuracy is not needed in a "for example if" explanation.

Let's presume the snow load is calculated to be 35 psf by the Case Study (just for an example), and that wet, saturated, snow weighs 21 pounds pcf (https://www.fema.gov/media-library-d...owload_508.pdf , see section 2.2.1), then a snow load of 35 psf means the depth of the snow at 21 pcf = 35/21 = 1.67 ft deep on a representative one square foot sample area of that snow load area.

While I didn't look for it, my recollection is that somewhere in Chapter 3 there is (at least used to be) which addressed snow load and the height of vents, etc., snow is not my thing, but you should be able to find it. I was up in NC for the month of October and it snowed one day about two weeks ago, and it snowed just enough to begin to accumlate on the roofs of cars and show white on the green grass ... being a Florida person most of my life, my color preference is the "green grass" (this probably also results from having spent my first 10 years 40 miles south of Buffalo, NY, where "white snow" seemed to be the predominate color - our average snowfall was 250 annually ... I no longer have a need to see 'white snow'.

I was under the understanding that the stack should have been 24" above the ridge.
Figure G2427.6.3, Termination Locations For Gas Vents With Listed Caps 12 Inches Or Less In Size At Least 8 Feet From A Vertical [obstruction]
- Roof Slope Flat to 6/12 = minimum height of 1.0 feet
- Roof Slope 6/12 to 7/12 = minimum height of 1.25 feet

And, of course
- G2427.6.1 Installation, general. Gas vents shall be installed in accordance with the manufacturer's instructions.

Sooo ... the minimum height of that vent is ...

Hope that helps on what I used those terms to try to represent.

5. ## Re: furnace vent height on roof

With all of the AHJs of the front range that I am familiar with, that flue vent is compliant for that roof pitch (as long as the actual opening of the flue, not the top of the cap, is 1' above the high side of the flue). We rarely get snows exceeding 12" (of course, when we do, they can be spectacular). Local requirements don't make us build for the exceptional situations such as the 3' snow of March, 2003. And in the real world, the heat of the flue keeps it clear. After that March, '03 snow, all furnace and water heater flues were sitting in wells melted out in the snow, with nary a problem. And a curious thing that I saw was that even the winterized homes had the flues and some of the plumbing vents open. Apparently, there was enough stored warmth inside the vacant homes from the previous sunny days that was venting out, to keep the flues clear.

Up in the mountains, some AHJs want to see 16-18".

Last edited by Lon Henderson; 11-11-2017 at 07:06 AM.

6. ## Re: furnace vent height on roof

The manufacturer of the vent is usually printed on top of the vent hood. The installation instructions are usually the same for all. Ameriivent mentions snow but I don't think Duravent does.

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