How to Insulate Massive Ash Dump Before Insert?

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jmon22

Member
Jan 2, 2017
9
Ohio
Good Morning All!

Getting ready to place an insert in my inefficient wood burning fireplace. I currently have an ash dump underneath that is leaking cold air badly that I want to insulate/seal up before doing so. The only problem is that it is over 5 feet long, almost 3 feet wide, and 12 feet deep. Couldn't believe it when I opened up for the first time.

What is the best way to manage this? Dump shake/rake insulation in to fill it up? Just seal the door as well as I can and not worry about insulating? Something else?

Appreciate any help you can give!
 

jatoxico

Minister of Fire
Aug 8, 2011
4,350
Long Island NY
I would use rockwool not the pink stuff. Its naturally mold resistant IIRC If used as intended where do you access the cleanout, from outside? Is so I think first insulate there heavily then air seal with whatever/however makes sense then insulate at the dump in the firebox just for good measure. I probably wouldn't feel the need to fill the entire void unless it somehow was a benefit.
 

jmon22

Member
Jan 2, 2017
9
Ohio
I would use rockwool not the pink stuff. Its naturally mold resistant IIRC If used as intended where do you access the cleanout, from outside? Is so I think first insulate there heavily then air seal with whatever/however makes sense then insulate at the dump in the firebox just for good measure. I probably wouldn't feel the need to fill the entire void unless it somehow was a benefit.

Correct. The only problem is that I only have the ash door on the inside and the cleanout on the outside and both are tiny. Not sure how I would get rock wool in/down there. Could shove batts I guess but they would just fall randomly.
 

xman23

Minister of Fire
Oct 7, 2008
2,347
Lackawaxen PA
This void sounds like the fireplace foundation that goes down to the footers. My concern with filling it is, If any water in there, and gets soaked up in the insulation, it will never dry out. Smelling bad, etc. Can you create access to this space from the basement or outside? It maybe usable space? If not, I don't know what I would do.
 

jmon22

Member
Jan 2, 2017
9
Ohio
This void sounds like the fireplace foundation that goes down to the footers. My concern with filling it is, If any water in there, and gets soaked up in the insulation, it will never dry out. Smelling bad, etc. Can you create access to this space from the basement or outside? It maybe usable space? If not, I don't know what I would do.

That may be the case, however I'm not sure why they have an ash dump going into it with an access door outside. There must have been services that emptied these out for you in the past.

It is behind a block wall in the basement so not worth opening to access. Perhaps just best to seal it off the best I can?
 

rwhite

Minister of Fire
Nov 8, 2011
1,802
North Central Idaho
I would get a piece of steel larger that the 7x9 opening and use high temp sealant to glue it down to the fireplace floor. Rock wool is pretty stiff. I would imagine you could wedge some in there fairly tight before you covered it. Maybe use some sealant to glue a 7x9 piece to the plate steel?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,077
central pa
Just stuff some insulation in the hole and cover the top with sheet metal siliconed down
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,480
South Puget Sound, WA
What insert is this for? Some have an option for outside air connection that could take advantage of the ash pit as a source of air.