Garage heater chimney help

[Michael85]

Hello!

I’ve been searching the internet for information / videos on this process for quite some time and have yet to come up with solutions so I’m hoping for assistance! I am installing a garage heater in my garage and have a vertical vent kit that needs to pass from the heated space, into the attic which has cellulose insulation blown into it and terminating out of the roof. The items I have are listed below followed by my specific questions.

Heater: Mr. Heater MHU80NG (F260560)

Vent Kit: Mr. Heater 4” vertical vent kit (F102848)
Vent kit includes:
(qty 1) 4 x 36 in. B vent pipe
(qty 2) 4 x 24 in. vent pipes
(qty 1) 4 in. 90° elbow
(qty 1) wall firestop
(qty 1) roof flashing
(qty 1) storm collar
(qty 1) vent cap

My issues/questions

1) Termination point for single wall vent to B-vent. Can this occur near the top of the attic space just before the pipe goes outside? Or does this have to happen prior to entering the attic space? I was only supplied with a single B-vent which would only reach the top roof flashing due to code for exterior requirements as explained in step 4. Essentially trying to figure out if I need to purchase more B-vent.

2) Wall firestop – this piece of steel is essentially useless unless I’m using B-vent through it from what I can tell. Code requires 6” of clearance around single wall vent and there is only approximately 2” of steel on 2 of the sides of the hole. So I believe that I cannot use this piece for attic stability unless I’m using the b-vent. Is that correct?

3) Assuming that I can use the Single wall vent into the attic, can I purchase 2x 24”x24” 26 gauge galvanized steel sheets and use a hole cutter to cut 4-1/8” holes in them and attach one to the bottom of the ceiling (removing the drywall and securing to the joists / framed box that I’ll make to keep insulation out). And then building a plywood box higher (approx. 12” tall) to maintain the air gap above the insulation and attach the 2nd plate up there for the vent pipe to pass through and keep insulation out? From videos online it appears as if you can make a vent box in the attic out of plywood / OSB as long as you keep the minimum clearances. 6” for Single wall and 2” for B-vent?

4) As for termination outside, I’m going with the guide which showed 3 ft from the HIGH side of the roof flashing as the minimum vertical height and 10 ft from the pipe to the point on the roof 2 ft down from the top of the b-vent. I have a 6/12 slope so unfortunately that ends up with a calculated value of 7 ft of b-vent.

I have to measure, but I think I can use the 2nd alternative which is 3ft minimum and 2 ft above the ridge cap. I’ll go into the attic soon and measure from the hole to the ridgeline to check.

With that in mind, at what height to I need to purchase some sort of bracing for the piping?

5) Do I just use 3x screws to screw the single wall vent to the other single wall vent and to the B-vent? Are there any concerns with putting screw holes into the vents or not?

Any assistance is appreciated since the instructions are basically useless.

Thanks,

 

[The Cobbler]

you transition to b-vent in the heated space close to the heater .
b-vent is not supposed to be screwed together . twist lock it & aluminum tape the joint if you want
b-vent is not industry standard, you need to use the same company thru ought the job, the pcs are not interchangeable
the fire stop has angles on it that fit into the area you cut out in the ceiling (clearance) .
my set up is
heater to a short pc of pipe, then transition to B-Vent , that into a b-vent T , with a clean out on the bottom, b-vent thru the ceiling with firestop, b vent thru roof with flanges, cap etc.
a bit of bracing in the attic space ( plumbers band snugged to b-vent with nuts & bolts.

 

[Michael85]

thanks for the reply. Can you speak to the image that I've attached. If the URL doesn't work, it's from the Mr. Heater install video on youtube called "Mr. Heater Unit Heater Installation & Operation" at 3:45.

I ask because it shows 24" Single wall vent pipe going into the attic? I guess the image could not actually be an attic though and instead be a heated upper story.

Thoughts?

Thanks

 

[The Cobbler]

I looked at your picture.
my install was done by me (as a helper & I hung the heater) , and my friends nephew that is a licensed gas guy. he put his name on the install . he said what we did is code.
I'm in Ontario .

 

[Michael85]

thanks for the reply. I checked again with different googling terms and find lots of areas stating that single wall vent should NOT be in the attic. So i'll buy extra b-vent to transition to at the ceiling and run that outside. Now I just need to determine how high my stack will be outside the roof.

 

[The Cobbler]

it's something like 30" above the highest point withing 10'

 

[Michael85]

fyi this is what I was referencing for the minimum requirements. Just need to figure out how high on the roofline my hole actually is to meet code then I'll order the b-vent that I need. I'll be using a 3" airspace rather than the minimum of 2" around as well in the attic.

 

[The Cobbler]

so you need minimum 3' high, and 24" higher from a point within 10' away .

 

[spudley]

Not exactly unless Canada follows different rules. The OP might want to check some B-vent termination tables for proper height above roof penetration. Only B-vent 14" or larger follows the 2' higher than anything within 10' rule.
A roof with a 7/12 or less pitch only requires a 1' above roof line termination, provided no adjacent wall or obstruction is within 8'. The height above roof line increases with pitch.
In heavy snow areas, might be wise to increase height.

 

[Michael85]

Interesting for sure. I'll see if I can track down the tables and find out. While I search, maybe someone here has a copy and can track me down the reference table? I'm using B vent pipe on a 6/12 slope roof and if I can avoid a 7' stack I'd love to. But I want to ensure this is safe and to code so if I have to i'll do it.

Does anyone here have a copy of CGA B149.1 Natural Gas and Propane Installation Code that would be able to take a look? The installation manual for the heater references the 10' requirement UNLESS otherwise specified in

CAN/CGA-B149 Installation Code. In an earlier paragraph it states "CSA" rather than "CGA" googling it, it seems like they are the same thing? Anybody know the difference here?

 

[D45]

It depends on the roof pitch as well, which may vary based on the brand of the vent. Follow the manufacturers installation manual with what vent kit you choose

 

[Michael85]

Thanks for that chart!

The installation manual says this:

The vent must extend at least 3’ (1m) above the highest point where it passes through a roof of a building and at least 2’ (0.6m) higher than any part of a building within a horizontal distance of 10’ (3.05m) unless otherwise specified by the (American) National Fuel Gas Code, ANSI Z223.1 or (Canada) CAN/CGA-B149 Installation Code. The vent must extend at least 5’ (1.6m) above the highest connected equipment flue collar.

Based on that I'm looking into what CAN/CGA-B149 says to see if it is different.

The bottom of the image shows "size according to expected snow depth". Is there an area that defines that more? Snow doesn't collect on my roof but I am in a snowy area.

is there a diagram associated with that table? is it 1 ft higher than the "peak" of the roofline or is it 1ft higher than where it penetrates the roof. Based on the wording, it appears as if it's just 1 ft higher than where it penetrates, regardless as to whether or not it is higher than the ridgeline.

also, is there a horizontal table requirement listed? Rather than just vertical?

Thanks!

 

[The Cobbler]

the vent must be at least 3' thru the roof . and 2' higher than anything that is within 10' of it horizontally
so if you exit at the peak, you need 3' above the peak
if you exit at the eaves, you need at least 3' , then measure 10' horizontall from there and you need to be at least 2' higher than that point

 

[spudley]

Looks like different b vent manufacturers use different criteria. I'm using AmeriVent available at Graingers which I believe also operates in Canada. The tables for AmeriVent are similar to the posted table from D45.
It also appears the Mr Heater vent kit suggests the venting requirements posted by Cobbler.
In any case I'd follow the recommendation of the manufacturer or read CAN/CGA-B149 Installation Code.
Good Luck.