"Chimney" vs "vent" code ambiguity

[jmarkwolf]

I've been confused regarding the height requirement above the slope of my roof for my hanging heater in my new detached garage.

The NFPA (national Fire Protection Association) cites two differing specs. One requires a 12ft or better high vent stack, the other requires a 4ft high vent stack. For obvious reasons, 4ft is more convenient than 12ft. See pics below.

The distinction appears to be for a "gas vent" vs a "chimney".

My application is a 4in diameter, B-vent stack from a Beacon-Morris, through a 12:12 pitch roof.

I think (and hope) Figure and Table 12.7.2 applies to my scenario, and not 12.6.2.1.

The "local authorities" always seem to be in a big fat hurry and don't seem to want to offer a "considered answer".

Can any HVAC guys on the forum offer any insight?

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[Heatdr]

Hi,I'm in NJ and the code here calls for 2 foot above anything within 10 feet.Does the beacon morris offer any other flue options,ie power vent,horizontal venting?

 

[jmarkwolf]

Hi,I'm in NJ and the code here calls for 2 foot above anything within 10 feet.Does the beacon morris offer any other flue options,ie power vent,horizontal venting?

It is a powered vent, and has category I or category III vent options.

I prefer to go through the roof (category I).

 

[jmarkwolf]

Hi,I'm in NJ and the code here calls for 2 foot above anything within 10 feet.Does the beacon morris offer any other flue options,ie power vent,horizontal venting?

That matches the requirements for "chimneys" and "single-wall metal pipes" as in the NFPA 12.6.2.1 I included in my original post.

The other scenario I included is different than this, requiring only 4 ft above a 12:12 pitch.

 

[Shop Specialties]

You are overthinking this. 3 foot above anything within 10 foot is good.

 

[mrobins297aaa]

unfortunately I don't think (7) applies to you, and although its described and written very poorly they are talking about vent stacks that are penetrating the roof next to air intake openings in wall/roofs.

the other picture you have there is the old standard code of 2' above the height of the roof with in 10' of the vent. I think that applies to you.

I'm not sure if the fact that you have a power vent you can reduce the height requirement. i would think you could but i don't know by how much.

 

[mrobins297aaa]

You are overthinking this. 3 foot above anything within 10 foot is good.

I don't think he's over thinking it..........at 3 foot above the anything with in 10' makes the vent 13' above the roof

 

[Shop Specialties]

The 3' is measured from the top of the pipe horizontal not vertical.

 

[mrobins297aaa]

your incorrect the 3' is a min. for flat roofs or ones with very little pitch.

you measure over horizontal 10' than vertically up to that point on the roof and then add 2' and that is the top of your stack, in op case he has a 12/12 roof so over 10' is also up 10' plus 2' would mean the top of the stack would have to be 12' above the roof.

 

[mrobins297aaa]

I think this is what your looking for, this is from the 2003 michigan mech code book
sec 804 it refers to power venting, take a look at 804.3.5 #6

enlarged view of #6

this would allow you to be 3' above the roof, if your having it inspected i would run it by the inspector first and see if he agree's.........

 

[mrobins297aaa]

The 3' is measured from the top of the pipe horizontal not vertical.

sorry, i take that back you are correct in so far as power venting, just not in the interpertation of the of the view posted by the op........which is actually for a natural vent appliance

 

[brewchief]

I have always used the gas vent chart in your situation, I'm dealing with the same inspector as well.