Insulating "firebox"

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egclassic

Feeling the Heat
Jan 1, 2011
261
SW Ohio
I was performing some pre-season cleaning of my insert this weekend; blowing dust from blower, vacuuming cobwebs etc. I had removed most of the surround to do this and it got me to thinking, since I have an exterior masonry chimney that the insert sits in, am I losing heat through the walls of the firebox, much the same as a basement type install? I thought about buying some Roxul and lining the sides and rear of stove, but thought I'd get some opinions first.
Could this cause the stove to overheat, and would I be unintentionally causing myself some other issues? Maybe its not neccesary at all, and I'm just over-thinking? Any how, thanks in advance!
 
Have you asked Harman?
 
Not sure what the manufacturer would say but it seems there have been several here that have done it. IMO I don't think it will help much. I'm not sure a whole lot of heat gets radiated past an insert jacket when the blower is running (but I have never measured it). I also want that mass of brick containing the insert to heat up and release it over time rather than stay cool.
 
...I also want that mass of brick containing the insert to heat up and release it over time rather than stay cool.

^^ From my own experience with exterior brick chimney, some of that stored heat is released to the outdoors.

A few insert insulations have been described in other threads. I think they are fairly convincing, and if I could do it, I would.
My chimney is on the north side of the house, and I can feel the cold behind the surround and insert. A chimney on the sunny side of the building might be OK.
Let us know what you discover.
 
I had a customer once who complained that their insert would not throw good heat. We thought it was his wood, so we brought out our own wood. Fired up the stove and as long as the air was open you could could get good heat but when you shut the air down for a long burn it would cool down a lot. The fireplace was downstairs on a outside wall.After two more call backs we finally decided to insulate the firebox with Mineral Wool. Guess what stove performance improved 100 percent, The brick and soil around firebox where absorbing that much heat from the firebox on low and slow burns. We attached the mineral wool bats to the masonry not the insert that way it didn't over heat the unit in any way just stopped the heat transfer to the outside.
 
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I have a free standing stove that is installed on the hearth and just slightly intrudes into the old fireplace firebox. I had about 40 bricks leftover from another job that I just stacked about 3" from the back of the fireplace about 5 bricks high. This seems to catch and keep more heat in the home. i would do it. That is the reason I went freestanding after a number of inserts.
 
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Do you have an insulated block-off plate? If not, that's good bang-for-the-buck and an easy way start.

I'm seriously thinking about insulating the firebox around my insert as well. The outer box of the insert does get up to temperature after a few solid hours of burning and releases heat off the top, back and sides. At first, I figured the thermal mass would release heat for a long time after the fire had died but this is just not the case. The truth is, it takes a really, really, really long time for the masonry to heat up and I don't feel like any of that heat radiates back to the house since it cools fairly quickly. There is just to much brick pulling the heat outward and upward. My insert is open, without a surround, so I suspect the affect would be worse when trapping the heat in the box with a surround in place.
 
First, check with the manufacturer. I have seen some inserts where they say no problem, put a blanket on it. I have seen others that say it needs air circulating around the box. Some even say not to run the insert too hot without the fan.

After getting the manufacturers opinion there are a number of options. First, if you don't have one already, an insulated block-off plate. If the manufacturer has no problems or concerns then you can put a blanket of mineral wool around the box. If the insert needs minimal clearance and air flow around it and you have the room you can put sheets of micor like mineral board on the bricks. It will act like an insulator and reflect the heat back to the stove while leaving an air gap to the stove.

But to repeat once more, first check with the manufacturer...

KaptJaq
 
I insulated my fireplace and saw a huge difference. Check the link in my sig to see install pics. Exterior chimneys suck up a lot of heat.
That is exactly what I was planning on doing, thanks for the pics.
Also, thanks to those with the idea of spraying the batts first to retain the fibers, wouldn't have thought of it myself.
 
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