Replies

1. 
   Guest_ | Jul 29, 2000 05:27pm | #1

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   Andy, you have an existing non masonry fireplace that you are replacing with another type? Is the pellet stove also rated for a zero clearance installation? What is the floor surface that you want to cover with a hearth? Joe H

2. 
   Andy_S. | Jul 30, 2000 05:48pm | #2

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   Joe:

   Thanks for the response. The floor surface is 3/4" plywood over which I have applied 1/4" hardibacker board. This runs from the rear of the freplace extending 24" outside the fireplace (ie. the hearth). Everything is as you have stated. It is a zero clearance insert being installed in a none masonary fireplace from which I have removed an old zero clearance wood insert. Here are the manufactureres clearances for this fireplace:

   Clearance from rear of insert to rear wall of fireplace: 1"
   Clearance from side of insert to side wall of fireplace: 6"
   Distance from insert to mantle: 18"

   None of these distances are any problem. The insert will extend 12 1/4" out of the fire place onto the hearth.

   Thanks again for any advice you can give.

3. 
   Guest_ | Jul 31, 2000 02:12am | #3

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   Andy, How tall is the insert you are putting in? Is it a stove on legs type thing? I've seen them sitting on the floor on metal pans & on a tile area also. I would guess the R value of ceramic tile at zero or close to it. Hardi backer might have some? Is it even rated? This sounds like a "Ask the manufacturer what is acceptable" or the supplier. Joe H

4. 
   Don_Hall | Aug 02, 2000 06:28am | #4

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   Another hearth construction question:

   I have buckets of small (2-3" diameter, 1/2" thick), very smooth stones that I want to use to build a hearth around a freestanding woodstove. Questions:

   What is suitable base material? The base of the stove stays cool. Is plywood okay?

   What should I use to adhere the stones to the base material?

   I would like the "grout" between the stones to be a dark blue or similar color. Is grout the right material to use, or something else?

5. 
   Guest_ | Aug 10, 2000 05:10am | #5

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   Is this a raised hearth? If so I can give you the details on the one I just did to meet the mfg. specs for my stove.

1. 
   Guest_ | Aug 11, 2000 12:16am | #6

   *Two comments:1: I was told, by the fireplace installer, that he simply uses one layer of concrete board for the fireplace and calls it done. This is in COMPLETE disregard for the instructions which call for about a foot of brick or stone for the hearth. So,....2: USG corporation (you know -- drywall and cement board) also sell a product with a high R value that you can use for the hearth because it is strong enough for floor tile. It ain't easy to find; I had to search their web site to find the info, call them for a local supplier (only 1 in the whole chicago area) and talk him into selling the stuff.This still means a certain amount of height above the floor for the hearth, so I hope your fireplace is raised off the ground.I don't have the information about the name here today. I will try to find it and post it early next week.

6. 
   Andy_S. | Aug 19, 2000 05:43am | #7

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   John: The fireplace installer might actually be right, depending on the specific appliance's specifications. He probably is right for my particular appliance, which is a pellet stove, and here is my reasoning. Upon further research I was able to find out that the minimum hearth specifications for the pellet stove I am planning to install is 3/8 inch thick millboard (whatever millboard is?) or equivalent with a K factor of K= 0.07 or a k factor of k= 0.84.

   K or k factors are thermal conductivity factors and are the way to relate different material's thermal conductivity. Without getting to complex: the k of concrete backer board is 0.98. The formula for relating millboard to concrete backerboard (or anything else for that matter) is:

   (k of alt./k of spec.) x spec.thickness = thickness necessary

   where:

   1. k of alt. is the k of alternate material(in this case concrete backer)
   2. k of spec. is the k of manufacturer's specified material
   3. spec. thickness is the manufacturer's specified thickness of material
   4. thickness necessary is the thickness of the alternate material, in this case concrete backer board.

   So therefore:

   (0.98/0.84) x (3/8") = required thickness

   Thus, 0.4375" (that is 7/16") is the required thickness for my particular appliance. This is less than the 1/2" thickness of many concrete backerboards such as Wonderboard(tm).

   To take this one step further, the k of common brick is 5.00. Using the above formula:

   (5.00/0.84) x 0.375 = thickness of brick required

   Thus I would need a minimum of 2.2 inches of common brick for this particular pellet stove.

   It takes much more brick than concrete backerboard because brick has a higher thermal conductivity than does concrete backer (that is a higher k or K). Another way to say it is that more heat is conducted to the subfloor by brick than by concrete backer.

7. 
   Andy_S. | Sep 01, 2000 04:16am | #8

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   I am planning on installing a pellet stove insert into an existing zero clearance fireplace in my home. There is presently no hearth. I wanted to construct a tile hearth using a Hardibacker Board. The manufacturer specifies an R rating of no less than 30 for the hearth. Does anyone have any ideas on how I can acheive an R rating of 30 for this hearth.

8. 
   Guest_ | Sep 01, 2000 04:16am | #9

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   Geeze O Petes!! Sounds like your installing a blast furnace. With the distances you have given for back and sides, what material(s) did you use?? The existing firebox opening is really arbitrary if your installing this as a freestanding unit. I guess I would start with the manufacturers suggestions for hearth material and construction. If your not getting anywhere there try the National Gypsum Association, or Lousiana Pacific, they make rated material for applications like yours.

   Good luck.