Insulation behind firebox

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ColoradoBob

New Member
Dec 4, 2024
5
G4$f1replace
I have an old Heatilator GC200 that goes out after running for half an hour or so. It looks like what is going on is there is fiberglass insulation with metallic backing insulation behind the firebox that has sagged and is blocking the air intake. Because of a bad tiling job, I can't really get to it except from the back around the exhaust, but I think I could slowly pull it out from the back. My question is whether this is something that came with a heatilator and should it even be there at all. I should note, I have EIFS siding (basically foamboard covered with stucco) so I'm a little concerned that if I remove it, the heat from the fire could damage the foam insulation and maybe that's why the fiberglass is even there. Any input would be appreciated.
 
Can you post a couple of pix of the situation?
Here you go. The copper wires were an attempt to make a spring to hold the insulation off of the wall to allow airflow. It seemed like it worked briefly. I can get about 30 minutes before the fire basically runs out of O2 and gets very sooty, eventually going out. What I'm debating trying is pulling the insulation via the air intake.

Fireplace
[Hearth.com] Insulation behind firebox


Exhaust/intake with the cover removed
[Hearth.com] Insulation behind firebox


You can see the insulation in the back.

[Hearth.com] Insulation behind firebox


[Hearth.com] Insulation behind firebox
 
That could be the issue. Can you access the intake of the venting from inside the firebox?
I'm sure that it is the issue. I guess the real question is whether the insulation is necessary, particularly since I have EIFS siding? I can't find anything that shows a fireplace having insulation on the back like that. I can't get to it from the inside since it's on the back of the firebox. I would have to remove the box and I can't do that unless I pull some of the stone around the fireplace, but at this point I'm less worried about the how to remove than I am whether I should remove it.
 
There should be NOTHING blocking the intake. Insulation in that area is not needed. The exhaust is the inner pipe & the fresh combustion airflow helps to keep the venting system from getting overly heated…
 
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There should be NOTHING blocking the intake. Insulation in that area is not needed. The exhaust is the inner pipe & the fresh combustion airflow helps to keep the venting system from getting overly heated…

That's kind of what I thought, the intake air should be cool so the gap between the the inner and outer edges of the intake should prevent the outer edge from being hot. And then there should be at least 3 1/2" space that the studs provide before you get to the EIFS substrate, which is probably OSB and should insulate the styrofoam even further. I may just see if I can pull the insulation out and give it a shot.
[Hearth.com] Insulation behind firebox
 
I got most of the insulation out and the fireplace seems to be working well. I just hope it wasn't there for a reason. (The upper side of the intake did get hot after running the fireplace for 30 minutes, but I could still touch it.) If it wasn't for the styrofoam component of EIFS I wouldn't worry about it at all.
 
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