Thread: Fireplace flue clearances

I could not find clearance requirements on these flues. They are for wood burning fireplaces.

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Typically 2" clearance to insulation and combustibles.
Did you see the fire-stop where it passes through the ceiling?

Jim,
Do you mean around the roof decking.

Originally Posted by mathew stouffer

Jim,
Do you mean around the roof decking.

No, due to the angle of the photo, it is not clear if there is a fire-stop plate at the ceiling level as required. There is not one required at the roof decking.
Upon looking closer, I think I do see the metal fire-stop on at least one of the pipes, but you were there.

2" are required for wood-burning appliance vents.

Originally Posted by A.D. Miller

2" are required for wood-burning appliance vents.

Matt - Actually, when you say flues you should be saying vents as A.D. referred to them.
The flue is the space inside a vent or flue liner.

Originally Posted by A.D. Miller

2" are required for wood-burning appliance vents.

Is this true for a triple wall vent?

Depends on the manufacturer specifications. This is normally on a tag attached to the vent or embossed into the metal itself, but it is almost never zero clearance without a thimble, etc.

Is that attic floor pitched or the photographer?;-)

It appears to be the listed factory Chimney for a factory built fireplace. As Eric pointed out, there are flues inside each chimney. Yes, I know but it is the lingo.....

How many offsets in this entire chimney?
Why the offset in the attic? Is this a return elbow back to plumb? These are return elbows as they have the unused straps attached. That would mean the chimney above that exits the roof should be plumb
No offsets from vertical greater than 30 degrees regardless how done. Is this?
The listed firestop does go on top of the attic joists in this case but-------- you need an attic insulation shield or vertical fireblocking according to building code.
Those appear to be combustion air kits behind the stacks---most AHJs will require them to be rigid pipe for 12" either side of a firestop/fireblock where it must be supported. An air kit cannot be above the level of its entry into the fireplace unless it first forms a trap or is listed that way. In any event, it cannot originate any closer than 36" to the flue gas outlet above.
Since there is plywood decking right up to these chimneys, you need to consider physical protection against banging into them. A simple pony wall with 1/4" ply or OSB would suffice but if you're going to do that, why not make vertical fireblocking and do it correctly?
All insulation must be cleared away and the pipe inspected up close. The clearance space is required to be stated on the listing stickers. It usually is 2" but some pipe may be less. If you cannot find a listing sticker or or clearance marking and the listed installation instructions are not available, then 2" would be your default for a solid fuel factory chimney.
Some mfrs. require screws into the joints of offsets. All mfrs. require support in offsets of 6' or greater. Some require EVERY offset joint to be supported. See the listing.
To be this close means there must be another offset below this point. There are regs. in the listed instructions for offsets such as min. height before any offset, min. system height for two offsets, max. offset lateral, etc. See the listed instructions.
Most importantly, those elbow straps are not being used. Elbow straps represent the entire support for chimney above a return elbow. Failure to use them is an extreme fire hazard. If the chimney settles down, it can blow apart a joint causing a fire---I've seen it enough. The straps should be per the listed instructions or angled up at a 45 deg. angle with 3 fasteners per strap--usually spec'd as 8d nails or equiv. Not drywall screws or roofing nails as they can pop. The straps should twang when you thumb them like a guitar string. If a strap is too short, you should provide sufficient framing in proximity rather than trying to extend straps as this would violate the listing.

These were just a few thoughts I had when I glanced at these pics. ;-)

Hope these are fuel for thought as Dale puts it.
Bob