BIS heat exchanger ducts and insulating

[qyota]

I have a Security Chimneys BIS model 1. It is installed in the lower level (split level house) on an external wall in a block/brick chimney and wood box. The block "box" that houses the pre-fab fireplace is not insulated. It has a door on the outside so you can chuck wood in, and door on the inside where you can grab the wood to feed the fire.

The top of these older BIS models have two large (8-inch?) ducts that attempt to divert fan-blown and convectively-warmed air from the bottom of the unit, out the top and into the room. That's great, but again the concrete block box that houses this unit is not insulated, and is thus about the same temp as the outside air.

I'd like to insulate that box as best I can, or at the very least, insulate the ducts. I plan to use Roxul to do this. I have access to the block box via the external wood-loading door, and I can easily stand up in the woodbox, at the side of the unit.

I assume this is safe to do, and that insulating these ducts will result in less heat loss to that cold block box. Right? Pics:

Outside view:



Exterior wood loading door:



Looking inside:



Other side of sheet metal divider:



Outside air, not yet hooked up:



Inside wood access door on left:

 

[begreen]

By insulating the box do you mean the sides of the BIS? I'd be concerned about overheating the fireplace that way. Perhaps use sheet Roxul and insulate the block walls?

 

[qyota]

I want to insulate the block, and the ducts that move warm air into the room.

 

[begreen]

That should work using Roxul sheets for the walls. After that the need to insulate the very short run (elbow) to the duct would probably not be necessary.

 

[qyota]

Hmm, gotta find somewhere around here that sells the roxul boards. I found only the batts today. The backside of the interior wall needs something too...maybe just drywall.

If I find those Roxul boards, I might just use my Remington .22 concrete nail shooter. Or, I suppose hi-tack adhesive works too.

 

[begreen]

The Remington might do better if shot through a large flat washer. Check with your local Home Depot, Lowes or lumberyard and ask if they can order Some Roxul Comfortboard 80 for you.