Hearth Pad

[Byron]

I have a question regarding a hearth pad for my Hearthstone Homestead with 4" legs. As you know, the stove has a high R-value requirement (6.6). Since I can't make clearance to my mantle with the stove sitting on the current pad, I need to move the stove out a bit over the hardwood floor. This, of course, means I need to build a hearth pad that will protect my floor. Here's my current plan. I really appreciate any and all feedback. (By the way, taking down the mantle is not an option.)

1" (+/-) flagstone
5/8" Thinset
1/2" HardiBacker
1" fiberglass insulation
1/2" HardiBacker
1" fiberglass insulation
1/2" Hardibacker

Based on my calculations, this will leave me with a hearth pad with an R-value of at least 7.44. I should also note I'm going to use specially cut pieces of HardiBacker immediately under the stove's legs to provide adequate support for its weight; this means Hardi-Backer will be stacked 3.5" ONLY immediately under the legs of the stove.

Does this setup sound good to go? Based on what I've read on this site, I know some people prefer Durock, etc. over HardiBacker; however, HardiBacker was the best option I could find locally and I already purchased the boards. Thanks, in advance, for your guidance!

 

[DriftWood]

Your at r=6.35 not 7.44

Areas under legs r= 0.11

Hardy backer is made of cellulose; I called James Hardie technical support 1-888-JHARDIE about the lack of R= 0 value off their ½ inch hardybacker product. They told me ½ inch hardybacker has no Rated R value, James Hardie technical support said “it conducts heat”. Hardy backer is not the stuff you want behind your stove or under it. WonderBoard or Durock cement boards are R rated and UL Listed for that application. I’ve only used Durock brand board because it is 100% cement with a fiberglass backing.

# note
1/4” hardi backer board is r0.13 per for specs check out this web limk to conform fire resistande and r-value

(broken link removed to http://www.jameshardie.com/homeowner/products_backerboard_halfInch.shtml)

R-value of the specified floor protector, then your setup is
acceptable. (Hearthstone)

Noncombustible Material Thickness R-value

Gypsum or plaster board > 1/2in. = 0.45
Wallboard, Wonderboard, or Durock> 1/2in. =0.20
Ceramic board (Fiberfrax or Micor) > 1/2in. =1.10
Nominal solid clay brick > 1in. =0.20
Ceramic wall or floor tile > 1/4in. =0.01
Mineral wool insulation > 1in. =3.12
Cement mortar > 1in. =0.20
Horizontal still air² > 1/8in.=0.92

1 According to Intertek Testing Services, Inc.
2 According to ASHRAE Handbook of Fundamentals
1977



1” (+/-) flagstone=.01
5/8” Thinset =.10
1/2” HardiBacker =0 not rated and not UL Listed for that application
1” fiberglass insulation =3.12 (if you use Mineral wool insulation (fire stop))
1/2” HardiBacker =0 not rated and not UL Listed for that application
1” fiberglass insulation=3.12 (if you use Mineral wool insulation (fire stop))
1/2” Hardibacker=0 not rated and not UL Listed for that application

Your at r=6.35 not 7.44

Areas under legs r= 0.11

 

[bcnu]

Welcome. My new Homestead was installed over the summer and I just started using it about two weeks ago - couldn't wait any longer for cold weather to try it out. So far it's great.
You're right about the high R value. You must be using the short leg version. I went through almost every possible plan to come up with what I needed. I was able to begin the hearth below the new wood floor we installed, but I had quite a chore getting it to code because we wanted to use an old mantle. I used micore 160 and Durock, with tile on top. I also used the longer legs so my R value was around 2.5. The stove sits just in front of my fireplace and we also used the surround kit and the upper heat shield to get enough clearance to the mantle. Sounds like your install is a bit different than mine. Let us know when you finish it. Would like to hear how it goes and find out how your stove is doing.

 

[DriftWood]

MICORE® Brand 300
r-value 1.09

http://www.acoustics.com/specs/USG_product/usg_spec.pdf#search=’micore 300 spec’

MICORE® Brand 300 Board from USG is a superior substrate for fabric and vinyl-covered wall panels, office
dividers and tack boards. An excellent core for chalkboards, stove boardsand similar applications, MICORE Brand
300 Board offers outstanding resilience, superior machinability, high “k” factor, heavy density and highest surface hardness of any MICORE

½” Durock
r=.26

(broken link removed to http://www.usg.com/USG_Marketing_Content/usg.com/web_files/Documents/Prod_Data_and_Submittal_Sheets/DrckCement_Board-Submittal_Sheet_CB399.pdf)

Composition and Materials DUROCK Cement Board is formed in a continuous process of aggregated portland cement slurry with polymercoated,
glass-fiber mesh completely encompassing edges, back and front surfaces. The edges are formed
smooth—patent No. 4,916,004. The ends are square cut.

Description
DUROCK® Brand Cement Board provides a smooth, sound base for glass and ceramic mosaics; ceramic and quarry
tile; lugged tile; and thin stone and thin brick. Suitable for application to wood or steel framing spaced 16
o.c. in
new construction and in remodeling. Board is ideal for use in partitions, walls, floors, soffits and ceilings in wet or
dry areas. It does not deteriorate in the presence of water so it is highly durable in high-moisture areas such as
baths, showers, kitchens and laundry rooms. Also adaptable for fences, fireplace fronts, mobile home skirting,
agricultural buildings,UL-listed wall shield/floor protectors, garage wainscoting and exterior finishes.

Limitations
A. DUROCK Cement Board is designed for positive or negative uniform loads up to 50 psf. For complete information
on the use of DUROCK panels in exterior systems, consult your USG sales representative.
B. Maximum stud spacing: 16” o.c. (24” o.c. for cavity shaft wall assembly); maximum allowable deflection, based
on stud properties only, L/360. Maximum fastener spacing: 8” o.c. for wood and steel framing; 6” o.c. for ceiling
applications.
C. Maximum dead load for ceiling system is 7.5 psf.
D. Steel framing must be 20-gauge or heavier.
E. Do not use drywall screws or drywall nails.
F. Do not use 5/16"DUROCK® Brand Underlayment for wall or ceiling applications.
G. Do not use DUROCK Cement Board with vinyl flooring.

My 2005 Hearthstone Heritage needs 1.2 r-value hearth pad. 5 sheets of ½” durock
OR
1 sheet of ½ “ durock+1 sheet of ½ “ MICORE® Brand 300 Board to cover the oak flooring in my house.

I put ½” micore 300 down first, then ½” durock and finished the top with stone tile.

 

[Byron]

Thanks so much for the feedback. Looks like I need to return the HardiBacker and seek Durock or Micore 300.

I know there's a difference between fiberglass and mineral wool insulation; however, will fiberglass insulation suffice? I didn't find mineral wool insulation at Lowe's, but I do have what I think is mineral wool insulation (Super-Felt insulation that says "fireproof" on the backing) in the attic of my 60-year-old home. I suppose I could swap the new roll of fiberglass insulation with some of the old stuff. Regardless, should I lay the insulation thick or loose in the 1"-deep area I create on the hearth pad?

One final question: Does the fact the r-value under the legs will be much lower than the r-value of the remainder of my hearth pad really matter? It seems to me the heat will not be directly transferred from the legs down through the supports and to the floor. If this were the case, the r-value for the Homestead with 6" legs should be the same, right? I suspect the stone and Thinset would help distribute the heat, as would all of the layers below the stove. The only way to avoid adding such supports would be to "sandwich" insulation between the Durock or whatever I use; however, I imagine this would compress the insulation so much it would lose much of its insulative qualities. Am I way off base here?

Thanks again!

 

[Gooserider]

The insulation value of fiberglass or rock wool depends on it NOT being compressed! It must be fluffed up to work properly, but that means you would be getting NO support for the Durock or other cement board, and your hearth will not have the needed structural strength. Micore 300 is not significantly compressible, and doesn't loose insulation value when used in a hearth construction - you can put it in a "sandwich" with Durock and have a solid, strong structure. I would loose the fiberglass and the Hardiebacker, go with Durock and Micore. This has the added advantage of letting you make the hearth pad thinner. The other option would be to swap the short legs for the taller ones - it actually works out that the increase in R-value called for by the short legs is the same thickness as the difference between the long legs and the short ones, so the stove top stays the same height...

Other good practices, though not required by code -

1. Incorporate a layer of thin sheet metal (I used aluminum roof flashing) into the sandwich. This will act as a heat spreader to dissipate any hot spots that develop.

2. In the area under the stove, minimize the number of screws, and use short screws that only go from one layer to the next, rather than going all the way through the entire sandwich, and stagger the screws slightly - this eliminates paths for direct conduction.

3. Use a layer of thinset between each layer of material, this fills gaps and eliminates voids, which ensures a more rigid structure (needed for good tile work) - The thinset holds the material UP, the screws hold it DOWN so that it can't move either way...

Gooserider

 

[Byron]

Thanks, Gooserider, for the great feedback!

 

[Byron]

OK, I've devised a new hearth pad plan that calls for Micore 300. That said, where can I find the stuff? How much does it cost? My hearth pad will be 3'x5'. I stopped by Home Depot this evening and the guy I spoke with looked at me like I was from another planet when I asked him about Micore; Lowe's here in Waynesboro, VA, doesn't carry Micore either.

Is there a kit that will allow me to add height to the 4" legs on my Homestead stove? If yes, I would assume adding a heat shield is also an option; would this further reduce the requirements for my hearth pad.

Thanks!

 

[DriftWood]

Micore® Distributors:

Quick Jump:
AL AZ CA CO CT FL GA IA ID IL IN KS MA MD ME MI MN MO NC NH NJ NV NY OH OK OR PA RI TX UT VA VT WA WI Other States



(broken link removed)

Call the Distributor closest to you. Some drywall suppliers carry it also, or know where to get it. I drove 60 mi one way for sheet I needed. Wood Stove retailers may have a supply on hand. Try them also.

 

[DriftWood]

Contact your Hearth stone dealer about the leg height you want. Two sizes appear to be available 6" and 4" he might swap them out if your stove is new or you could just buy a set of 6 inchers and bolt then on...


Install your Freestanding stove with 6” legs with the floor
heat shield on one of the following:

o A hearth pad listed to UL 1618 standards. These are
noncombustible floor protectors; no other type of floor
protector is acceptable.

o A composite (homemade) floor protector with an
R-value of 2.5 or more.



Install your Hearth Mount stove with 4-inch legs on one
of the following:

o A noncombustible floor, such as a slab, cement, or
stone hearth. (A noncombustible floor will not ignite,
burn, support combustion, or release flammable
vapors when subjected to fire or the anticipated heat
from your stove.)

o A floor protector with an R-value of 6.6 or more that
you obtain from your dealer. (A floor protector is any
Quality Home Heating Products Inc® 10 Homestead Models #8570F and #8570H
noncombustible on the floor underneath and extending
to the front, sides, and rear of the wood stove.)

(broken link removed to http://www.hearthstonestoves.com/documents/Homestead8570Manual.pdf)

 

[Byron]

I found a Micore 300 supplier about 1.5 hours from my house ($35.20 per 4'x8'x1.5" sheet), as well as a place about 30 minutes away that will charge more per sheet ($40.69 per 4'x8'x1.5" sheet). I just got a call back from another place even closer to home that may be able to get access to Micore 300; however, the price is in an unknown and the guy said he would be able to get back with me on Monday with numbers.

Another question: Can you cut Micore to size without altering the integrity of it? I assume the answer is yes, but I figured I'd ask anyway -- especially since I will need to cut the 4x8 down to 3x5 to meet my needs.

Thanks again for the feedback.

 

[Gooserider]

I found a Micore 300 supplier about 1.5 hours from my house ($35.20 per 4'x8'x1.5" sheet), as well as a place about 30 minutes away that will charge more per sheet ($40.69 per 4'x8'x1.5" sheet). I just got a call back from another place even closer to home that may be able to get access to Micore 300; however, the price is in an unknown and the guy said he would be able to get back with me on Monday with numbers.

Another question: Can you cut Micore to size without altering the integrity of it? I assume the answer is yes, but I figured I'd ask anyway -- especially since I will need to cut the 4x8 down to 3x5 to meet my needs.

Thanks again for the feedback.

Far as I know, cutting it is no problem, though I'd probably want to avoid breathing any dust from the cutting process. I haven't looked at the MSDS, but I suspect the dust would not be healthy stuff... If possible, I'd probably want to cut it with a utility knife, possibly with the "score and snap" method if that's appropriate. (I haven't actually worked w/ Micore myself to get the hands on...) Obviously you WOULD reduce the benefit by trying to plane it down or reduce it's thickness, but that doesn't sound like what you want to do.

Gooserider

 

[bcnu]

micore easy to work with - no problem cutting it. I could not get the micore 300 so settled for micore 160. Only difference is a lower r value.

 

[Byron]

OK, here's another question as I continue to contemplate my installation. What precisely constitutes a noncombustible floor? According the the manual, I must install my stove on a floor protector with an R-value of at least 6.6 (as discussed above in the thread) OR "A noncombustible floor, such as a slab, cement, or stone hearth." I have a hearth pad in front of my fireplace that sits flush to the floor. The hearth is topped with ceramic tile. Beneath the ceramic tile is about six inches of poured cement. The cement "block" is supported on the bottom by wood joists. The joists come into contact with the cement only on the edges. Is this a problem in terms of the supporting joists potentially being exposed to unsafe levels of heat? Does my hearth pad qualify as a noncombustible floor? Thanks!

 

[Highbeam]

The six inches of poured cement has an R-value which may or may not be 6.6. The poured slab is similar to a raised hearth. You must have some stout joists to support a 6" thick slab.

 

[Gooserider]

OK, here's another question as I continue to contemplate my installation. What precisely constitutes a noncombustible floor? According the the manual, I must install my stove on a floor protector with an R-value of at least 6.6 (as discussed above in the thread) OR "A noncombustible floor, such as a slab, cement, or stone hearth." I have a hearth pad in front of my fireplace that sits flush to the floor. The hearth is topped with ceramic tile. Beneath the ceramic tile is about six inches of poured cement. The cement "block" is supported on the bottom by wood joists. The joists come into contact with the cement only on the edges. Is this a problem in terms of the supporting joists potentially being exposed to unsafe levels of heat? Does my hearth pad qualify as a noncombustible floor? Thanks!

I don't know about an "Official" definition, but I know that in my VC manuals, they define a "non-combustible floor" as one that contains NO combustible materials, such as concrete over bare earth. Given the R6.6 requirement, and the fact that concrete is not real high R-value, I suspect strongly that this is what Hearthstone intends. In most useages, a slab would be poured over dirt, or at least they used to be before all the insulation stuff has gotten (deservedly) popular, and a cement or stone hearth could be referring to something built on a solid footing with no wood in it.

IOW, I wouldn't want to go with the "non-combustible floor" option given your description.

Gooserider

 

[bcnu]

maybe I missed this but can you use the longer legs? My Hearthstone required 2.5r with the longer legs.

 

[Byron]

I picked up the 6" legs today, which should solve my issues. A bottom heat shield is included in the package. I didn't realize this was an option when I posted much of what I did in this thread.

Another question: Which is better for a heat deflector, galvanized steel or aluminum? I plan to screw some sort of metal to my fireplace opening to serve as a deflector for rising heat. My stove will sit less than 36" from the mantle and I want added protection.

Thanks!

 

[bcnu]

Our stove sits just in front of the fireplace. I bought the metal surround and heat shield"( top) that is an option for the Homestead. That allowed me to reduce distance from stove top to mantle by 12" (from 35" to 23") Code was very specific and is shown in the install manual which was available online. I've always thought of the mantle as the top part of the wooden surround. We had a part of the surround, 12 inches below the top. It sticks out more than 1", therefore that was the place I had to use for the 23" above stovetop measurement.

 

[Gooserider]

I picked up the 6" legs today, which should solve my issues. A bottom heat shield is included in the package. I didn't realize this was an option when I posted much of what I did in this thread.

Another question: Which is better for a heat deflector, galvanized steel or aluminum? I plan to screw some sort of metal to my fireplace opening to serve as a deflector for rising heat. My stove will sit less than 36" from the mantle and I want added protection.

Thanks!

There probably isn't a signifcant difference in function as a deflector, both will do that job about the same. I would expect the Aluminum might look better since it's a more uniform material, but that depends on your tastes and the setup.

Gooserider