New Insert and Hearth/Surround Re-do

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Good to know . This may be a ridiculous question, but what Is considered “combustible” within the chimney? Creosote on the chimney walls? I have heard about chimney fires…..
It’s not inside the chimney. Interior chimney has no structure outside the house. Think center of home Exterior chimney has a has structure outside, think along an exterior wall.

So the combustibles in question are usually framing, joists and roof sheeting. None of which can be in contact with the chimney and to meet code needs the minimum clearances listed above. Mine doesn’t. So I have insulated liners.
 
Good to know . This may be a ridiculous question, but what Is considered “combustible” within the chimney? Creosote on the chimney walls? I have heard about chimney fires…..
Inside yes creosote is combustible. But I am talking about outside the chimney not inside
 
Doesn’t a full masonry chimney provide the necessary mechanical barrier required?
Mechanical yes thermal no. Which is why clearances are required
 
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Doesn’t a full masonry chimney provide the necessary mechanical barrier required?
Only if it was built with 2" clearance (interior) or 1" (exterior) from combustibles.
 
Can you elaborate on the chimney clearance to combustibles? @bholler or @begreen. I feel I am misunderstanding it.

So for example, a house with an external chimney. The chimney is going to be in contact with the siding or sheathing as it goes up the house. The siding will abutt the chimney. Same with roofing sheathing. How does that 1" apply? Does it mean the face of the chimney as it connects to the house towards any framing or walls etc?

I'm just curious how it's actually measured. In my head for some reason I can't seem to make sense of how any chimney could meet that requirement. How could it be safe to have an open fire sending tons of heat up a clay lined flue but adding a SS liner inside the clay lining for a stove would require insulation for the same flue gas temps?

That just doesn't make sense to me. What am I missing? Full disclosure I'm also very tired and I'm sure it's obvious lol.
 
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This is good to know. I always assumed that the masonry was also a thermal barrier as it doesn't seem to be a good heat conductor. I'm learning lots here. Thanks guys!
With a 2000 degree chimney fire in the chimney that masonry isn't enough of a thermal barrier.
 
Can you elaborate on the chimney clearance to combustibles? @bholler or @begreen. I feel I am misunderstanding it.

So for example, a house with an external chimney. The chimney is going to be in contact with the siding or sheathing as it goes up the house. The siding will abutt the chimney. Same with roofing sheathing. How does that 1" apply? Does it mean the face of the chimney as it connects to the house towards any framing or walls etc?

I'm just curious how it's actually measured. In my head for some reason I can't seem to make sense of how any chimney could meet that requirement. How could it be safe to have an open fire sending tons of heat up a clay lined flue but adding a SS liner inside the clay lining for a stove would require insulation for the same flue gas temps?

That just doesn't make sense to me. What am I missing? Full disclosure I'm also very tired and I'm sure it's obvious lol.
Trim can touch the corners of the chimney otherwise clearances need to be maintained. It is very hard to build that way which is why it is so uncommon
 
Trim can touch the corners of the chimney otherwise clearances need to be maintained. It is very hard to build that way which is why it is so uncommon

So basically the siding, trim, roof can touch the corners of the chimney but the side facing the house needs to have a 1" gap to combustibles for exterior chimneys. That makes sense. I was missing the corner aspect.
 
So basically the siding, trim, roof can touch the corners of the chimney but the side facing the house needs to have a 1" gap to combustibles for exterior chimneys. That makes sense. I was missing the corner aspect.
Yes and an internal one needs 2" all around
 
Yes and an internal one needs 2" all around
One more question if I could:

So does that mean, for an external chimney for example, the roofing ends 1" before the chimney and the flashing covers that gap? Or does it abbut the chimney and then also has flashing. Roofing materials are combustible but a 1" gap is sizable (2" for the internals) gap for flashing to cover up.

Again, ty for taking the time. I enjoy learning the fine details of this stuff.
 
One more question if I could:

So does that mean, for an external chimney for example, the roofing ends 1" before the chimney and the flashing covers that gap? Or does it abbut the chimney and then also has flashing. Roofing materials are combustible but a 1" gap is sizable (2" for the internals) gap for flashing to cover up.

Again, ty for taking the time. I enjoy learning the fine details of this stuff.
I think firestops are allowed to touch as well but I would have to double check.
 
Is it safe to say that a "chimney fire" is anything that catches fire AROUND a chimney? I thought it was fire within. Still learning. #NoBurnNovember.
A chimney fire is inside the chimney it it catches things around the chimney that is then a structure fire and what all of this is meant to avoid
 
Sorry, guys, I'm probably getting off in the weeds here. One of my "burning" questions is what it takes to cut a hole in a heat form for 120VAC for the blower motor. Is that DIY-able?
 
So creosote? What is the initial burn source that's not wood in the firebox to cause a chimney fire?
What do you mean? The initial fire source is the wood.
 
I initially took the term "chimney fire" too literally and was thinking of a fire WITHIN the chimney, rather than heat radiating FROM the chimney causing adjacent combustibles to burn. I get it now.
I think the term chimney fire does indicate an uncontrollable fire of creosote within the flue. It is really hot and can lead to a failure of the system resulting in fire spreading to combustibles closest to the chimney. So if you don’t have any combustibles In contact with the chimney is much safer.
 
I initially took the term "chimney fire" too literally and was thinking of a fire WITHIN the chimney, rather than heat radiating FROM the chimney causing adjacent combustibles to burn. I get it now.
No a chimney fire is a fire in the chimney. If it's outside the chimney it is a structure fire
 
I think the term chimney fire does indicate an uncontrollable fire of creosote within the flue. It is really hot and can lead to a failure of the system resulting in fire spreading to combustibles closest to the chimney. So if you don’t have any combustibles In contact with the chimney is much safer.
Not just uncontrollable. And fire in the chimney is a chimney fire. There also doesn't need to be any failure of the system. The chimney can be perfectly intact but transmit enough heat through the masonry to cause ignition. That is the reason for the clearance requirements.
 
Sorry, guys, I'm probably getting off in the weeds here. One of my "burning" questions is what it takes to cut a hole in a heat form for 120VAC for the blower motor. Is that DIY-able?
Wait, what is the plan here?
 
There are already holes to channel air from a blower in a heat form. But once you install an insert there won't be much of any heat there. And the heat form will be cut up to fit the liner through.
 
I see the air channels on the sides of the heat form but thought I needed to mount a receptacle through the steel firebox to plug the blower in to. Is that problematic other than cutting the steel?