Fisher Grandma bear Hearth

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tsimms

New Member
Feb 26, 2021
33
New York
Hello,
I made some progress on my grandma bear project. Definitely behind schedule though.

Originally my stove had a rear 8" flue that I had cut out and blocked off. I had the welder install a 6" top flue and it came out great. I refinished the stove. Sanded it down and gave it a nice clean fresh coat of stove bright paint. It really looks nice.
I now have the stove in my living room and I decided where I want it to live.

I have all the information on the chimney components, i just need to order it all. I will be using Duravent DVL with the through the ceiling kit and then from northland express.





OK, so my next step here is making a hearth pad and back shield. I plan on using coultured stone on the back and slate type of tile on the base. I'm going to build my base using 2x4's, durock on top then tile. Do I need to double or triple the durock for the base? Sheet metal?

For the behind heat shield, I'm not sure exactly how to go about this part... I have 1" ceramic spacers. . Do I need multiple layers of durock? Sheetmetal?
Will I need to remove the sheetrock from the wall and install durock in its place? and then build my heat shield 1" away from it?
I do have an electrical outlet where the heat shield will go. Do i need to remove it?

My stove measures 25 1/2" wide X 24" deep
What should I keep my clearances at? I will be using the telescoping DVL pipe up to the ceiling.. How wide should I build this hearth? How high? How far from wall?

Any information and help with this is greatly appreciated.
Thank you all in advance
Tim
 

tsimms

New Member
Feb 26, 2021
33
New York
20210924_165628.jpg 20210923_101928.jpg 20210923_100622.jpg
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
I use double cement board, then solid brick for floor protection. (Extend 18 inches in all directions from stove) Double cement board with tile gets quite hot in the center under stove, so I add a steel heat shield under stove an inch or so below stove bottom that keeps the finish tile floor protection much cooler. The manual called for sheet metal and equivalent of 3/8 asbestos mill board with solid brick covering. So I use double cement board in place of the mill board.

The material of the heat shield only needs to be non-combustible. 1 inch air space behind it, raised on spacers like bricks for air intake at bottom, and open at top to allow heated air to rise out. No wall fasteners in centerline of stove. Setting rock board on spacers only requires wall spacers to maintain the air space. They do not support weight.
The size of shield must be large enough that any measurement from stove to unprotected wall is 36 inches. Simply use a yard stick on any angle from stove to anything combustible.

Clearance to single wall pipe needs to be 18 inches to unprotected wall. If closer, double wall “close clearance pipe“ needs to be used for reduced clearance down to 6 inch minimum.
 
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tsimms

New Member
Feb 26, 2021
33
New York
Thank you Coaly.
The hearth will end up being bigger than I originally thought.. that's ok though.
What do you think about the chimney components I listed?

There is 1 outlet that will probably end up being right behind the back of the hearth. Will I need to move that? I'll probably move it either way but just curious.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,109
central pa
Thank you Coaly.
The hearth will end up being bigger than I originally thought.. that's ok though.
What do you think about the chimney components I listed?

There is 1 outlet that will probably end up being right behind the back of the hearth. Will I need to move that? I'll probably move it either way but just curious.
You do realize you will absolutely not be able to use that screen with the stove being run on 6". And it looks like it will be a fairly short chimney you may have smoke issues even without the screen.
 

tsimms

New Member
Feb 26, 2021
33
New York
You do realize you will absolutely not be able to use that screen with the stove being run on 6". And it looks like it will be a fairly short chimney you may have smoke issues even without the screen.
Well Mr. Bholler. I sure hope that is not the case.
I was told by several people and previous posts here that it wouldn't be a problem. I'm not going to know until I fire it up.
We will see
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
26,109
central pa
Well Mr. Bholler. I sure hope that is not the case.
I was told by several people and previous posts here that it wouldn't be a problem. I'm not going to know until I fire it up.
We will see
Some people get away with them on 6" just fine but I have seen enough issues with them on 6" that I will never install one that way or recommend it. I find they work best on 7"
 

tsimms

New Member
Feb 26, 2021
33
New York
I use double cement board, then solid brick for floor protection. (Extend 18 inches in all directions from stove) Double cement board with tile gets quite hot in the center under stove, so I add a steel heat shield under stove an inch or so below stove bottom that keeps the finish tile floor protection much cooler. The manual called for sheet metal and equivalent of 3/8 asbestos mill board with solid brick covering. So I use double cement board in place of the mill board.

The material of the heat shield only needs to be non-combustible. 1 inch air space behind it, raised on spacers like bricks for air intake at bottom, and open at top to allow heated air to rise out. No wall fasteners in centerline of stove. Setting rock board on spacers only requires wall spacers to maintain the air space. They do not support weight.
The size of shield must be large enough that any measurement from stove to unprotected wall is 36 inches. Simply use a yard stick on any angle from stove to anything combustible.

Clearance to single wall pipe needs to be 18 inches to unprotected wall. If closer, double wall “close clearance pipe“ needs to be used for reduced clearance down to 6 inch minimum.

What distance do I need to keep away from the heat shield directly behind the stove? I will be using cultured stone and I'd like to keep as close as I can. From what I can see from the Fisher owners manual it says 36". Will building the heat shield with a 1" air gap help me reduce this? I will be using the DVL pipe as well
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
Thank you Coaly.
The hearth will end up being bigger than I originally thought.. that's ok though.
What do you think about the chimney components I listed?

There is 1 outlet that will probably end up being right behind the back of the hearth. Will I need to move that? I'll probably move it either way but just curious.
Good choice of chimney components.

A straight up installation with the reduced diameter worked fine testing my Grandma and Grandpa adding baffles.

The wall behind the shield stays cool. I would move the outlet since it is unknown how it is wired for future service. When speed wiring is used with push in connection instead of using the screws, they need to be accessible.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
What distance do I need to keep away from the heat shield directly behind the stove? I will be using cultured stone and I'd like to keep as close as I can. From what I can see from the Fisher owners manual it says 36". Will building the heat shield with a 1" air gap help me reduce this? I will be using the DVL pipe as well
Clearance is measured to combustible wall, not shield.

Attaching non-combustible material to a combustible wall is not a heat shield. It is still considered a combustible wall. Only an air space behind shield makes it an approved heat shield. It must be raised off the floor at bottom and open at top for air flow. Air is what cools the wall, not the material used.

Solid brick in contact with wall reduces the required 36 inch clearance by 33% down to 24 inches. (Refer to chart in NFPA 211 for reduced clearances)

A UL Approved heat shield as specified in NFPA 211 for unlisted appliances (as I described) allows 66% reduction down to 12 inches to combustible wall. That 12 inch is the minimum no matter what else you do.
The size of the shield must be large enough that you cannot measure 36 inches in any direction from the stove to combustible wall or material. So angle from stove upward to wall and sideways in all directions to maintain the 36 inch clearance. That gives you the shield height and width needed for the stove.

Be advised legally for a new installation most states have adopted the International family of codes. The Mechanical Code that covers solid fuel appliances and venting now specifies ALL appliances being installed must be UL approved with UL tag attached.
Simply Google “Building codes” for the state you are in for the building code adopted for any area of the US and Canada.
 

tsimms

New Member
Feb 26, 2021
33
New York
Clearance is measured to combustible wall, not shield.

Attaching non-combustible material to a combustible wall is not a heat shield. It is still considered a combustible wall. Only an air space behind shield makes it an approved heat shield. It must be raised off the floor at bottom and open at top for air flow. Air is what cools the wall, not the material used.

Solid brick in contact with wall reduces the required 36 inch clearance by 33% down to 24 inches. (Refer to chart in NFPA 211 for reduced clearances)

A UL Approved heat shield as specified in NFPA 211 for unlisted appliances (as I described) allows 66% reduction down to 12 inches to combustible wall. That 12 inch is the minimum no matter what else you do.
The size of the shield must be large enough that you cannot measure 36 inches in any direction from the stove to combustible wall or material. So angle from stove upward to wall and sideways in all directions to maintain the 36 inch clearance. That gives you the shield height and width needed for the stove.

Be advised legally for a new installation most states have adopted the International family of codes. The Mechanical Code that covers solid fuel appliances and venting now specifies ALL appliances being installed must be UL approved with UL tag attached.
Simply Google “Building codes” for the state you are in for the building code adopted for any area of the US and Canada.
Thank you..
I made a crude drawing of my interpretation of the clearances.
Does this look like I am correct with the proper clearances ?

20211001_070809.jpg
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
Thank you..
I made a crude drawing of my interpretation of the clearances.
Does this look like I am correct with the proper clearances ?

View attachment 282524
The 36 in all directions is to the combustible wall, not shield. (or anything else combustible)
 
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tsimms

New Member
Feb 26, 2021
33
New York
The 36 in all directions is to the combustible wall, not shield. (or anything else combustible)

Got ya... thank you.. Everything else looks right then I guess.?

As far as the heat shield on the wall. I'm trying to figure out how to fasten it. Can I double up strips of the 1/2 durock and fasten them to through the sheetrock into the studs? How about metal studs? and then fasten the double layer of durock over the top of them?
There would be airflow from the bottom up through the top but not from side to side like there would be if I used ceramic spacers. Would that be ok?
How much of the side needs to be exposed for airflow?

Once the durock is complete can I have a certain amount of cultured stone that goes all the way down to the base for support? Keeping 1" air gap most of the way along the bottom? I'm thinking both corners and maybe 2 evenly spaced pieces that go down to the base to add structural integrity.
How much of the bottom needs to be exposed for airflow?

Thank you again and sorry for all of these questions. I'd like to do this once and not have to tear it down to rebuild it. Or worse, burn my house down.. God forbid...
Just trying to get it right.
 

tsimms

New Member
Feb 26, 2021
33
New York
The 36 in all directions is to the combustible wall, not shield. (or anything else combustible)

So, if I have this stove on a flat wall in the middle of a room, no corner walls anywhere near it.
How wide does this heat shield need to be?
My stove is 25 1/2" wide. If I have 12" between the back wall and back of the stove with a heat shield between, does the heat shield need to extend 36" from the sides of the stove to the heat shields furthest distance?
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
The sides of shield can be closed. Hot air rises out the top. Airflow is bottom to top. Normally the heat shield is only single thickness cement board. Spacers must be non-combustible. Cement board spacers are ok but should not be directly behind stove. With the sides closed with cement board strips, you only need spacers as wide as the stove corners, not directly behind it.
1 inch opening is minimum at bottom, open at top.
When you set the shield on brick or spacers you’ll find it doesn’t take much to hold it from wall. I prefer the ceramic spacers in the kits, but you can make your own with copper tubing and washers. Cement board does conduct heat and transfer it to wall, so never use it doubled in strips directly behind stove. I sat a piece of rock board close to a burning stove, and in time the back felt just as hot as the side facing the stove. That is why the floor protection goes by resistance to heat flow as well as conductance. The Standard (NFPA 211) only calls for non combustible spacers. I feel the less contact the better. The wall spacers only stabilize the shield and prevent flex.

Measuring on an angle as you pictured at stove top is done sideways in all directions for the shield sides as well as top. With stove 12 inches from wall, mark the wall at 36 inches angled from stove in all directions. That is the minimum size of heat shield.

de002f2.gif
 
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tsimms

New Member
Feb 26, 2021
33
New York
So if I don't know if I'm doing this correct but here is what I came up with.
36" from each side and top. I marked the wall with blue tape.
Does this look correct? Its huge.
7'6".. across.
Does the base need to as wide?

20211002_150201.jpg
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
The floor protection needs to be 18 inches In all directions.

That doesn’t look right. I think you measured straight out from stove perpendicular to wall?

If you have a yard stick, with stove placed a foot from wall, touch the rear stove corner with the end of yard stick. Holding the yard stick level, swing the yard stick until it touches the wall. Mark where the yard stick touches wall while still touching stove corner.

The arrows on the drawing I posted above is the yard stick touching the stove and wall.

When you build a shield that size, no part of the stove will be closer than 36 inches to the unprotected wall.
The farther away the stove is from wall, the smaller the shield.
 

tsimms

New Member
Feb 26, 2021
33
New York
The floor protection needs to be 18 inches In all directions.

That doesn’t look right. I think you measured straight out from stove perpendicular to wall?

If you have a yard stick, with stove placed a foot from wall, touch the rear stove corner with the end of yard stick. Holding the yard stick level, swing the yard stick until it touches the wall. Mark where the yard stick touches wall while still touching stove corner.

The arrows on the drawing I posted above is the yard stick touching the stove and wall.

When you build a shield that size, no part of the stove will be closer than 36 inches to the unprotected wall.
The farther away the stove is from wall, the smaller the shield.

That's what I did. 36" from the corner of the stove to the wall.
It's a lot bigger than I thought I would need.
Like I said it ended up being 7'6" wide.
Seems overkill.

I might have to change location due to the size of the heat shield.

Our old stove was a Better n Ben's. We used a pre fab heat shield that was way smaller than this.
Other than moving the stove further away from the wall is there anything that would make it possible to go smaller with the heat shield?
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
It does look huge in your pic.

Brick directly in contact on that wall reduces clearance down to 24. With stove 12 inches from wall see what size the shield needs to be at 24 inches from stove corners to wall. That would be the shield size behind stove with wall bricked if that’s feasible.

See what size the shield needs to be at 18 inches from wall.

If you could measure the 36 inches to unprotected wall around the shield with your old stove it wasn’t big enough.
 
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tsimms

New Member
Feb 26, 2021
33
New York
24" from each corner of the stove is WAY better..

Does this have to be brick or will the stone suffice? I think the stone ledge rock I'd like to use is 1" thick
What about double or even triple up the cement board and then this stone? + air gap?

If brick is used, are you not required to leave an airgap? Just install brick over sheetrock?
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
There is a table of tested materials in the section for reducing clearance in NFPA 211.
The brick tested is solid full width brick in contact with combustible wall that gives 33% reduction from 36 down to 24 inches. This is not a heat shield. The shield uses air circulation for cooling.

Since you are trying to reduce the heat shield size I was suggesting covering the entire wall with brick, then if you want the stove 12 inches away you only need the shield the size for the 24 inch clearance. That clearance is measured to studs, not the brick.
Double or triple cement board with stone may or may not be enough protection. The keyword is tested and approved. If the material was not tested, it is not approved even though it may work. I think the benchmark surface temperature for test criteria is 117*f. over ambient air temperature. That is where pyrolysis starts to take place. It chemically changes the material, removing moisture to a lower ignition temperature. It is not reversible. So it is not an issue of igniting right away, as many will claim they have closer clearance than required working fine..... it is a matter of time that lowers the ignition temperature until it ignites. Charcoal is a good example of a material that has reduced ignition temperature.
 
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tsimms

New Member
Feb 26, 2021
33
New York
There is a table of tested materials in the section for reducing clearance in NFPA 211.
The brick tested is solid full width brick in contact with combustible wall that gives 33% reduction from 36 down to 24 inches. This is not a heat shield. The shield uses air circulation for cooling.

Since you are trying to reduce the heat shield size I was suggesting covering the entire wall with brick, then if you want the stove 12 inches away you only need the shield the size for the 24 inch clearance. That clearance is measured to studs, not the brick.
Double or triple cement board with stone may or may not be enough protection. The keyword is tested and approved. If the material was not tested, it is not approved even though it may work. I think the benchmark surface temperature for test criteria is 117*f. over ambient air temperature. That is where pyrolysis starts to take place. It chemically changes the material, removing moisture to a lower ignition temperature. It is not reversible. So it is not an issue of igniting right away, as many will claim they have closer clearance than required working fine..... it is a matter of time that lowers the ignition temperature until it ignites. Charcoal is a good example of a material that has reduced ignition temperature.

Thank you Coaly.. I misunderstood at first. To add brick to the entire wall will not be an option here.
Either I build it the way I have it in the picture with blue tape or move it completely to a different room. I'm going to have to think about it and make a decision.
Newer stoves reduce clearances , don't they? I guess that could be an option too. Even though I just refinished this 1.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,342
NE PA
Yes, they have metal shields on the stove to reduce clearances. That would work on an older stove easily, but since they were not tested with what you add, it would not be UL approved.
 

tsimms

New Member
Feb 26, 2021
33
New York
Yes, they have metal shields on the stove to reduce clearances. That would work on an older stove easily, but since they were not tested with what you add, it would not be UL approved.
I was saying maybe I would just get a new stove with better clearance but I really don't think I will do that.
Either I'm going to just go with it or change locations.
I do have another room that would really be perfect for not just the stove but the heat shield at that 7'6" wide.
It would require alot more work though. I'd have to remove 2 windows and a door and install a door where a window was.
I'd have to redo the ceiling as well.
I'm definitely glad I laid this out with tape first.