Roxul/rockwool around insert

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Torgul83

New Member
Mar 13, 2022
33
North castle Ny
Hello all. I have an osburn3500 insert on an interior wall with a 24 ft flue. Unfortunately, the installer did not put in a block off plate. Instead, roxul is stuff pretty snuggly around the throat of the flue. It will be too much for me to pull the insert myself and fabricate a damper seal. I'm thinking to just add more roxul on top of the insert. And while I'm at it, add some roxul on the back and side of the insert as I have maybe 5 inches on the sides and 3 inches of play in the back of prefab steel fp firebox where the insert is inserted. I figure this added insulation around the insert can harness heat more and keep the stove temp up higher so the fan runs longer. I understand I can run the risk of over heating the stove.
Any thoughts? Would this measure make any difference or is it a stretch? With the insert being on an interior wall, how necessary is the block off plate?
Thank you

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FramerJ

Member
Mar 18, 2021
64
Missouri
This is a great question and I would love to hear what others have to say. Last winter was my first burning wood so I am not qualified to answer. I have the exact same scenario. About a month ago I planned to pull out my insert to install a block off plate. I removed the surround, the bricks, the baffle, the door and started to question my decision. My insert was already a very tight fit and I didnt think it was worth the effort for what I would be gaining. Its my understanding that a block off plate keeps cold air from coming down from the chimney and keeps the heated air in, for the most part. It makes sense for a stove placed in a large fireplace but an insert (at least mine) is basically a stove inside a metal box so putting another piece of metal (block off plate) above seemed unnecessary for keeping the heat in. So to keep the cold air out I did the same as you and stuffed some roxul in the opening around the flue pipe. I would think if you install insulation around your insert you would definetely need to use your fan. I could be wrong about all of this so hopefully others will chime in.
 

Torgul83

New Member
Mar 13, 2022
33
North castle Ny
This is a great question and I would love to hear what others have to say. Last winter was my first burning wood so I am not qualified to answer. I have the exact same scenario. About a month ago I planned to pull out my insert to install a block off plate. I removed the surround, the bricks, the baffle, the door and started to question my decision. My insert was already a very tight fit and I didnt think it was worth the effort for what I would be gaining. Its my understanding that a block off plate keeps cold air from coming down from the chimney and keeps the heated air in, for the most part. It makes sense for a stove placed in a large fireplace but an insert (at least mine) is basically a stove inside a metal box so putting another piece of metal (block off plate) above seemed unnecessary for keeping the heat in. So to keep the cold air out I did the same as you and stuffed some roxul in the opening around the flue pipe. I would think if you install insulation around your insert you would definetely need to use your fan. I could be wrong about all of this so hopefully others will chime in.
Thank you very much for the response. You mentioned insulating the stove with roxul would definitely cause me to use my fan. I may have misunderstood that statement but I felt insulating around it would trigger the fan to run sooner and for longer periods since it is heat sensor activated. Being that it is an insert, we heavily rely on the fan. What do you think?
 
Last edited:

begreen

Mooderator
Staff member
Nov 18, 2005
96,414
South Puget Sound, WA
The insulation around the liner is better than nothing for containing heat in the fireplace cavity. It's ok to put some insulation behind the insert to further reduce heat loss, but I don't think putting it on top is a good idea. This has been backed up by some mfg. when asked. A 2 piece block-off plate could still be installed if there is room to get your arms up there.
 

kborndale

Feeling the Heat
Oct 9, 2008
468
LI
The tried and true method is to put in a block off plate. Insulation can be used with the plate.