Woodstove floor protector / R value ??

[ejb]

Hi guys.

I am looking to build a "pad" for my woodstove to sit on. It must meet or exceed code, and the code requires I do what the manual says.

The manual says I need a "noncombustible" floor protector with an r-value of at least 1.2.

It includes the attached table that shows the r-value of different materials I can use...surprisingly, ceramic tile is only 0.01, so I would need 120 layers of it to get to 1.2...airspace is listed as .94, but not sure how I can use that...

Anyway, I want to start with a 3/4 piece of plywood on the bottom and build up from there. I am thinking 3/4 plywood (does not count to R-value), 3- 1/2" thick sheets of gypsum board (.45 each) and then 1/2 cement board (0.20) topped by ceramic tile 0.01 for a total value of 1.56...

How does that sound? Suggestions/comments?

Chart also lists fiberfrax and micor in 1/2 thickness having a value of 1.1...but I have no idea where to buy these...anyone?

 

[Slacker]

Hi guys.

I am looking to build a "pad" for my woodstove to sit on. It must meet or exceed code, and the code requires I do what the manual says.

The manual says I need a "noncombustible" floor protector with an r-value of at least 1.2.

It includes the attached table that shows the r-value of different materials I can use...surprisingly, ceramic tile is only 0.01, so I would need 120 layers of it to get to 1.2...airspace is listed as .94, but not sure how I can use that...

Anyway, I want to start with a 3/4 piece of plywood on the bottom and build up from there. I am thinking 3/4 plywood (does not count to R-value), 3- 1/2" thick sheets of gypsum board (.45 each) and then 1/2 cement board (0.20) topped by ceramic tile 0.01 for a total value of 1.56...

How does that sound? Suggestions/comments?

Chart also lists fiberfrax and micor in 1/2 thickness having a value of 1.1...but I have no idea where to buy these...anyone?

How about the cement board then a layer of red bricks? Trim it with 1x4 oak.
Thats how I did mine and it looks great (to me). I broke 6 bricks in half to offset every other line of them. Bricks were free. I used a dab of liquid nail under the corner bricks to keep things in place while I trimmed it up.

 

[ejb]

How about the cement board then a layer of red bricks? Trim it with 1x4 oak.
Thats how I did mine and it looks great (to me). I broke 6 bricks in half to offset every other line of them. Bricks were free. I used a dab of liquid nail under the corner bricks to keep things in place while I trimmed it up.

I think that would look nice, but not pass code for my stove. Cement board plus brick don't seem to add up to a "safe" value of 1.2 or more in my case.

 

[Highbeam]

I see that you have purchased a Hearthstone, perhaps even a Heritage like I have.

You may not use sheetrock when the table calls out gypsum. The paper is combustible. So scratch that.

You have a couple of realistic options:

You can stack 6 layers of durock/wonderboard and then top with tile. Durock weighs 96 lbs per 3x5' sheet and is pretty easy to work with. This stack will be 3 inches tall and not very movable. Note the required hearth pad dimensions are pretty big with the side door.

You can try and find micore which is a soft foam board type stuff and is not suitable for tile or for the stove feet. You'll need to top the micore with a layer of durock and then tile. This is a great option if you can find micore. I couldn't find it in my entire state so I chose the next option.

Use an air gap. The horizontal still air gives great R-value, is cheap, is lightweight, and you can build it easily. I actually used steel 2x4 studs on edge to build a platform (remember, non-combustible stuff only) and then put two layers of durock on top of that followed by tile.

You can create an air gap with strips of durock as well but I went steel. The stove must be supported and it is a heavy dog. The airspace is horizontal STILL air meaning you dno't need to vent it in any way. Compare it to the layer of air between the glass of a double pane window.

Plenty R-value there and the raised hearth has grown on us. I originally wanted a low hearth but quickly found that it wasn't going to happen with the high R-value requirement from Hearthstone.

 

[ejb]

Yep, Hearthstone heritage (used it all last year but now I need to get it correctly installed)...great stove.

I was thinking that 2" of concrete was going to be too heavy, by my calcs I would need almost 4 cubic feet of concrete at about 130lbs per cubic feet...almost 600lbs, but 6 layers of durock would be the same (almost).

I was leaning towards the gypsum, but didn't consider the paper facing - I'll need to reseach that more. I also haven't been able to locate micor or fibrefrax sheets anywhere...

Can you elaborate more on the airspace...does it need to be a sealed air cavity? If air works so well, why could I just put all 4 legs up on a 2" brick and pickup 2" of air space which would exceed the r-value...must be more complicated than that.

 

[ToadHill]

I built a raised pad about 6" off the floor. I covered it with cement board and then put on ceramic tile with a foam backing ( I got it from the stove place, it's made for this purpose. I drilled 1" holes in the front and left a 1" gap in back to clear the wall. The stove and riser have been in for over 20 years and all has been fine.

 

[scott_vt]

I see that you have purchased a Hearthstone, perhaps even a Heritage like I have.

Mornin Beam,
I fell in love with that stove the moment I saw it !!! I have their website in my favorites under buildings ! When I put the addition on the backside of the Vt house I plan on getting that stove !

HearthStone Wood Stoves

 

[Highbeam]

The heritage is cranking along as we speak. We really like the stove. I recognized the R-chart that you had posted since I too spent some time with it.

I actually dealt with the Hearthstone tech man quite a bit since this air space issue was a bit new to me. He, Jim, was very helpful and would gladly send a clarifying letter from Hearthstone about the airspace if I wanted it. I do not think it needs to be sealed, or vented, just a gap of air. My worry was the other way, I didn't want to vent it and that was fine. I have seen elevated hearths that are more like low steel tables made of noncombusibles and they passed in their jurisdictions. You still need to have the hearth pad dimensions right and that eliminates the raised brick idea though it was a good thought. Using bricks to create the airspace below a layer of durock might work but I would prefer two inch wide strips of durock every 12" or so as a more stable air gap creator. My theory is that the air gap must be below a solid surface that will act as a heat shield to block radiant heat, then the air gap eliminates the conduction, then since this whole mess is below the stove convection is eliminated.

Remember that the hearth pad made of solid durock might add up to 600 lbs but then you have a 500# stove, the connector pipe weight,two guys lifting it, and maybe even a full load of firewood. There will be a good amount of weight involved which is a good benefit of the airspace. A solid subfloor is so important. Just imagine what would happen if itfell through while cooking along at 500 with a full load of firewood ablaze.

Oh hey and don't forget that there are some companies that make these hearth pads with adequate R-values for this stove. The manufactured hearthpads use magic to accomplish this and still be portable. I wanted a big hearth so I site built mine.

I attached some photos of my steel stud work plus the durock layers.

Scott: The bloody stove is made in Vermont. Go check them out. I would have loved a factory tour. So set down your syrup making machinery and take a look. The only other similar stove maker with soapstone is the woodstock stove which is also a fine product. It uses a catalytic converter and has larger clearances to combustibles though. Soapstone is where it's at. I showed my wife the Hearthstone website and she thought they were nice but our big steel Lopi was doing OK. When I showed her the stoves in person seh was gung ho! They really have a nice presence, with good cast iron castings and the stone.

 

[scott_vt]

The heritage is cranking along as we speak.

Scott: The bloody stove is made in Vermont. Go check them out. I would have loved a factory tour. So set down your syrup making machinery and take a look. The only other similar stove maker with soapstone is the woodstock stove which is also a fine product. It uses a catalytic converter and has larger clearances to combustibles though. Soapstone is where it's at. I showed my wife the Hearthstone website and she thought they were nice but our big steel Lopi was doing OK. When I showed her the stoves in person seh was gung ho! They really have a nice presence, with good cast iron castings and the stone.

Afternoon Beam,
While I have you answering questions, I see that the Heritage model will heat 1900 sq ft ! The addition Im eventually planning is going to be 18 x 30 maybe a bit more with two bedrooms above. So Im probablly looking at 1100 sq ft or maybe a bit more. My question is do you think that stove would be too big for that area ? I just really like the looks of the Heritage over all the other models, although all the stoves are very nice !

 

[randy41]

i think the stove's legs take care of the clearance issue.