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Clearance to combustibles

2K views 26 replies 8 participants last post by  supers05 
#1 ·
The stainless double-wall chimney (7" Duravent) from the coal boiler in the basement passes within 1.5" of one of the floor joists holding up my garage slab.

Here's the view from above:


The view from below:


Would a piece of cement board on the right sight be adequate or would I need to notch out that joist?

The boiler is already piped, and the horizontal spacing between the joists is only 12-5/8", so I wouldn't gain much by moving the boiler 5/16" to the left.
 
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#3 ·
Here double wall only requires 1" clearance to a combustible surface. Single wall requires 6". Local codes may vary.

Rural and absent local codes, How long has it been that way with no problems? Can you touch it when the boiler is burning?
 
#5 · (Edited)
Here, manufacturer's instructions will supercede the NFPA, but the manufacturer (Simpson?) specifies 2 inches to combustibles.

Which would be the safest installation, sheet metal on 1" spacers or cement board? Maybe I could put some sort of spacer behind the cement board.

I haven't ever fired up this boiler, so I'm not sure about the heat transmitted.

Also, do I need a firestop of some sort where the chimney goes through the garage slab? The portion of the chimney in the garage will be enclosed by a chase. The space in the framing won't accommodate a manufactured firestop.
 
#6 · (Edited)
I would be concerned what your insurance company has to say not net advisers. If they insist on the manufacturers specs then so be it. If they give you a waiver because it will weaken the structure and OK cement board I would use it.

If there is a fire then the fire dept investigator may find it. Not likely as it will be burnt but you never know. No waiver and you may have problems with insurance.
 
#8 · (Edited)
I don't know.

Also depends on what type of fuel you are using. Are you burning coal or oil or gas with conversion burners? The flue temp of gas should be the lowest and maybe they will let you get away with less clearance.

Talk to the fire inspector as they have the final say and the ins company.

The Dept. of Labor makes the rules where I am but it varies from Provinvce or State to State and probably town/municipality to others.
 
#9 ·
Here the strictest of the codes is what superceeds. So it's either manufacture, csa, or whatever else, that is more strict. But we can make the firestop out of sheet metal when needed. It's always required here. And the insurance company always has to sign off or you won't have insurance when it comes to things like that. I know people that had trouble getting the insurance to sign off for wood stoves. Had to add cement board with 1" spacers, even though codes were satisfied.

Cheers!
 
#10 ·
Who set this thing up? Having the flue pipe of a boiler going through the garage is such a bad idea. The garage needs to be isolated from the house so a running car doesn't allow exhaust gases into the house.
 
#12 ·
It is very common to get a negative pressure in a house. If you have exhaust fumes from the garage they will get sucked into the house. Just need to seal around the chimney to garage area with a proper plate to floor connection and high temp silicone at the chimney and plate area. Not ideal but it is what it is.
 
#14 ·
benjamincall said:
The boiler is under the garage, but the boiler room is pretty isolated from the rest of the basement. CO is less dense than air, so I'm not too concerned about anybody asphyxiating down there. The garage doesn't have any living space above it.
Carbon Monoxide is slightly lighter than air, but barely (sg=0.9667), making it neutrally buoyant. Depending on conditions, it can pool low, high, in the middle or just all over.
 
#15 ·
I'm pretty sure the enclosed and finished chase will do a good job of preventing infiltration of CO into my enclosed boiler room, since it will probably be tighter than the firewall and door between the garage and the house

The insurance companies I spoke with don't perform much of a chimney inspection, and the fire inspector in our small town won't be back in the office for another week, so I think I'm going to line the joists with cement board and use cement board spacers. I wish I could find some asbestos board.
 
#16 ·
CO can permeate anywhere and it does. The real problem with CO is that your lungs well much more readily absorb CO into the blood stream than O2 . So even small concentrations in the air can poison you quickly by replacing the O2 in your blood stream with CO.

Perhaps your system will work but quite frankly I want my fuel burning appliances to have lots of fresh air and went quickly. Whether that is a closed loop system or a natural venting chimney. As far as clearances to combustibles , I don't want my house to be an experiment or testing the limits of design.
 
#17 ·
Good thing the garage is a couple of feet too short for my vehicles.

Unfortunately, one of my helpers framed up that opening 3/8" of an inch small. Demolishing the garage and removing the slab isn't an option at this point. The chimney is 1.5" from a floor joist, so I wonder if 1/2" cement board on spacers would be a conservative solution. 2" is the required clearance to combustibles for this double-walled pipe.
 
#20 ·
Actually I'm not worried about the car, that's easy to fix. I'm worried about the fines and liability of the chimney. We have strict laws here and sometimes have to refuse work to protect ourselves. Maybe no one will notice in the future but don't be startled if someone you call for service walks away from it.


Cheers!
 
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