[Cultcab]

My sister just purchased a townhouse that has a large (12 foot) crawlspace under the living area. I was down there checking for leaks/dry rot/termite damage/etc. and I noticed that the insulation behind her fireplace (pellet) has been pulled out. There is about 4 inches behind the fireplace back wall and the studs. The insulation (3.5 inch R11) that is still there is blackened, but most has been pulled out and now it's just open framing behind the fireplace. I would like to replace the insulation, but I want to avoid the same problems.

What is the best insulation to use? Is a 4 inch gap between the back of the fireplace and the insulation sufficient?

 

[joecaption]

Need some pictures.
Not sure how if your under the house your seeing where the insulation is missing in the wall behind the stove.
Was it black from mold or from being charred?

 

[Cultcab]

I will take some pictures next time I head over there.

This is a 12 foot "crawl" space and most of the area behind the stove is exposed.

The remaining installation appears to be charred.

 

[Cultcab]

I have attached two pictures of this area - these are taken from the crawlspace area looking towards the back of the fireplace. You can see the metal box, the area where the insulation was removed, and the charred insulation.

 

[Windows on Wash]

What is the venting like?

That looks like standard HVAC sheet metal.

 

[Cultcab]

I can't see the venting - will that change the insulation that's needed?

It appears to be standard sheet metal used for HVAC applications.

Do I need to use a special type of insulation with this proximity to the metal box?

 

[TheEplumber]

Find the install manual or use Google to get it. Within the manual locate the clearance from combustionable surfaces table. Keep your insulation out of that zone and you should be fine.

 

[Cultcab]

I won't be able to access the manual for this. The fireplace box is original (the house was built in 1979) but the pellet stove was installed several years later. The manual for the stove does not reference any clearance requirements because it was installed inside the original box.

 

[Windows on Wash]

Still need to know how the flue venting is handled. If this is just a box that a double wall flue goes up through, you can seal and insulate right to that sheet metal, but without knowing, you can't get a real and factual recommendation.