New Grandma Bear install

[Frankdozer]

I’m installing a Grandma Bear in my house. The back will be against a brick chimney. There are no combustible surfaces near it concerning the back, front and 2 sides. Also I’m making a new 2” thick bluestone hearth on laminate flooring. What are the minimum clearances concerning all the above ? Thanks in advance.
Frank

 

[coaly]

I believe 3 inches was determined to be enough clearance for airflow to prevent uneven heating of sheets.

 

[Frankdozer]

Against a brick chimney, what would be the minimum hearth dimensions for a top flue Grandma Bear?

 

[coaly]

Series I unlisted, or later UL Listed?

 

[Frankdozer]

series 1 unlisted

 

[Frankdozer]

it will be installed here

 

[coaly]

Page 7 here; https://www.hearth.com/images/uploads/Fisher_Manual.pdf

 

[Frankdozer]

Thanks Coaly. I’m thinking of using 1.25” granite for the hearth, the same as used on countertops. Is this ok? The granite would lay on laminate flooring. The laminate flooring is on top of 11/32” plywood. The plywood is on top of 1” board. I really can’t find any info concerning hearth material and thickness.

 

[coaly]

Thanks Coaly. I’m thinking of using 1.25” granite for the hearth, the same as used on countertops. Is this ok? The granite would lay on laminate flooring. The laminate flooring is on top of 11/32” plywood. The plywood is on top of 1” board. I really can’t find any info concerning hearth material and thickness.

A search of granite r-value shows .05 to .08 per inch. This is because granite has high thermal conductivity. You will need double cement board over the combustible material, then use the granite like brick over the cement board.

This calculation is from page 2 in the manual requiring the minimum of 3/8 asbestos millboard or equivalent. Just noticed it gives the Grandma Bear hearth dimensions as 41 1/2 X 47 as well.

Realize this is before UL became the recognized National testing standard, and this manual is pre UL as well as the stove.

New installations as per NFPA-211 now require 18 inches in all directions. Normally the manufacturer manual trumps code, but I’m not sure about pre UL manual information. I believe technically it would be grandfathered if installed pre UL, or what NFPA required then, but a new installation needs to be to today’s standards.

Asbestos millboard was the industry standard, and Fisher manuals specify solid brick over 3/8 asbestos millboard, which the two layers of cement board would be the equivalent.

 

[Frankdozer]

All great info Coaly, I do appreciate it ! So as I understand, on top of my wood / laminate flooring, if I put 2 layers of 3/8 cement board then 1.25 inches of granite … then I’m good for floor protection per code ?

 

[coaly]

2 layers of 1/2 inch cement board under the granite.

 

[Frankdozer]

2 layers of 1/2” Durock. Ordered the 1.25” granite today to go on top. Wondering if I need a sheetmetal plate somewhere under the Durock.

 

[coaly]

I only use sheet metal when there are seams not staggered or unfinished joints.