Hearth extension

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Marc77

New Member
Sep 3, 2021
2
Canada
Hello, I need some clarification concerning the hearth extension for a wood insert.

Here is a quote from the manufacturer: "COMBUSTIBLE FLOOR MUST BE PROTECTED BY NON-COMBUSTIBLE MATERIAL EXTENDING (E) 16 IN / 405MM TO FRONT AND (G) 8IN / 205MM TO SIDES FROM FUEL DOOR. IN CANADA MUST EXTEND 18” TO FRONT. THERMAL INSULATION WITH A R VALUE = 1.4 AT A DISTANCE OF 18" FROM FRONT OF DOOR OPENING FOR CANADA AND 16" FOR USA. IF UNIT RAISED 4.5" FROM FLOOR, NO THERMAL INSULATION IS REQUIRED."

My insert will be sitting on the old firebrick which in fact raises the fireplace off the concrete floor by about 5". The hearth will be built at the same height as the top of the firebrick as per the installers reccomendation. Is the hearth considered the floor height or not, meaning do I need to meet the rediculous 1.4 R value? Never thought there was so much thought into a hearth extension, originally I was just planning on a box covered with plywood then capped off with slate tile. Any help is greatly appreciated as this is supposed to be my project for this weekend.

For reference, the fireplace wood insert is a Regency, model Alterra.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,200
central pa
Hello, I need some clarification concerning the hearth extension for a wood insert.

Here is a quote from the manufacturer: "COMBUSTIBLE FLOOR MUST BE PROTECTED BY NON-COMBUSTIBLE MATERIAL EXTENDING (E) 16 IN / 405MM TO FRONT AND (G) 8IN / 205MM TO SIDES FROM FUEL DOOR. IN CANADA MUST EXTEND 18” TO FRONT. THERMAL INSULATION WITH A R VALUE = 1.4 AT A DISTANCE OF 18" FROM FRONT OF DOOR OPENING FOR CANADA AND 16" FOR USA. IF UNIT RAISED 4.5" FROM FLOOR, NO THERMAL INSULATION IS REQUIRED."

My insert will be sitting on the old firebrick which in fact raises the fireplace off the concrete floor by about 5". The hearth will be built at the same height as the top of the firebrick as per the installers reccomendation. Is the hearth considered the floor height or not, meaning do I need to meet the rediculous 1.4 R value? Never thought there was so much thought into a hearth extension, originally I was just planning on a box covered with plywood then capped off with slate tile. Any help is greatly appreciated as this is supposed to be my project for this weekend.

For reference, the fireplace wood insert is a Regency, model Alterra.
Will the stove be atleast 4.5" above the combustible floor?
 

Marc77

New Member
Sep 3, 2021
2
Canada
Will the stove be atleast 4.5" above the combustible floor?
Not once the dricore and hardwood go down, i'll be at 3.5" approx. Would it be easier to throw in some 1" firebricks under the insert to raise it, this would give me the height. If I do it this way can I just go with my plan of using plywood and slate tile? I'll be honest, alot of this doesn't make sense to me,I guess i'm just having trouble comprhending why all this is necessary, seems like major overkill.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,200
central pa
Not once the dricore and hardwood go down, i'll be at 3.5" approx. Would it be easier to throw in some 1" firebricks under the insert to raise it, this would give me the height. If I do it this way can I just go with my plan of using plywood and slate tile? I'll be honest, alot of this doesn't make sense to me,I guess i'm just having trouble comprhending why all this is necessary, seems like major overkill.
It probably would be easier to do that yes. But the hearth extension will need to be atleast the 4.5" lower as well.

It is nessecary because they determined through testing what is safe. If the hearth extension is to high it will get to much radiant heat from the glass so it needs insulation so the combustible material under it doesn't combust.
 

EbS-P

Minister of Fire
Jan 19, 2019
1,504
SE North Carolina
Here is diagram from another insert manual. Pictures help. Use your raised height of 4.5” (F in the diagrams) and R value of 1.4 If you can raise the insert that would be ideal. The raised height is measured from bottom of insert to top of floor/hearth extension. So you need to take into account the thickness of the extension(and flooring you will add underneath it) when measuring.
Evan

7F46C371-3C56-4766-B328-7629E291836C.png
 

EbS-P

Minister of Fire
Jan 19, 2019
1,504
SE North Carolina
originally I was just planning on a box covered with plywood then capped off with slate tile.
Adding enough micro-core to get 1.4 under the slate is a possible option.