Building a Hearth

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naughted

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Feb 4, 2007
24
I need to tap the brains of the experts. I need to build a Hearth and according to the manual it needs to be made of a UL Listed material. A pre-made hearth will not work for me so I need to build my own. I wanted to make it out of slate or tile but could not find anything that stated it was a UL Listed material. I then decided I would use brick but again nothing stating it was UL Listed except for firebrick. Anyone have any ideas how to build a compliant hearth? What materials to use, how thick it needs to be? Any help is greatly appreciated.

Ed
 
For that size stove, two sheets of cement board with tile/slate top would be more than enough. Not sure what they mean by UL listed. Unless they are talking about the prefab stove boards etc. Those are UL listed. Im sure others will chime in with more technical info soon.
 
They should list an R value that you need to meet, along with required clearances in you manual. I'm no expert on how to achieve this, based on the materials you use, but there are others here who can help with that.

You may want to re-name the thread, including the stove you have. I'm sure that Mike will pick up on it and be able to help with the requirements.

BTW, welcome to the forum.
 
Okay, I bought a 4x8 sheet of 3/4 in. plywood to double up for the bottom layer, so with a 4 x 4 hearth I can get 1 1/2" in height. I have 2 sheets of 1/2" Durock for the next 2 layers which will get me an additional 1" in height and also acts as the insulator, and 3/8" slate tile. This will give me a roughly 4' x 4' hearth almost 3" thick. I'm thinking this should provide a compliant hearth for a Englander 25-PVDC Pellet Stove. Anyone see any holes in my plan?
 
naughted said:
I need to tap the brains of the experts. I need to build a Hearth and according to the manual it needs to be made of a UL Listed material. A pre-made hearth will not work for me so I need to build my own. I wanted to make it out of slate or tile but could not find anything that stated it was a UL Listed material. I then decided I would use brick but again nothing stating it was UL Listed except for firebrick. Anyone have any ideas how to build a compliant hearth? What materials to use, how thick it needs to be? Any help is greatly appreciated.

Ed

As mentioned earlier, the first step is to look in your manual and find where it describes the required R-value for the floor protection, along with the needed dimensions. This will vary with the stove or insert brand and model, it doesn't hurt to 'overbuild' if you think you'd ever want to put something bigger in, and I would especially consider any clearances in front of doors to be minimums that it won't hurt to exceed.

You then need to build a "sandwich" out of appropriate fireproof materials to meet or exceed that listed value. A handy "cheat sheat" on the various common materials is this one put out by one of our other Hearth.com members. It isn't mentioned, but many people consider it good practice to incorporate a layer of sheet metal into the sandwich to help dissipate any hot spots. Once you've designed your sandwich, it is a simple matter of covering it with your choice of non-flammable stone, tile, etc.

Micore is very soft, so most people that use it put it under a layer of Durock. Micore can also be hard to find and is on the expensive side.

Probably the most common approach is to use several layers of durock covered with whatever tile you like - note that you might as well ignore the value for the tile, as it really won't significantly increase anything.

It is OK to put wood molding around the outside edge as trim, so long as the dimensions INSIDE the molding meet the minimum clearances, though I'd advise going for an inch or two extra.

If you want a hearth that is flush with the surrounding floor, it is possible to cut out carpeting and subfloor as needed to make the depth for the sandwich, and this is where Micore works really well.

For a raised hearth, it is probably easier / cheaper to do the durock stack approach. If you want a really tall raised hearth, many people put a frame of steel studs down first, insulate between the studs with unfaced fiberglass, and then build the durock sandwich on top of the studs.

It is also important to check with your building inspector about what kinds of documentation and/or intermediate inspections he will want to proove that you have met the standards, also how you should document the construction so that if you ever want to replace the stove there will be a record showing what the existing hearth offers for protection. Otherwise you might have to rip it up just to show it was done right.

There are lots of threads in the forums on hearth construction, use the search engines to find them.

Gooserider
 
naughted said:
I need to tap the brains of the experts. I need to build a Hearth and according to the manual it needs to be made of a UL Listed material. A pre-made hearth will not work for me so I need to build my own. I wanted to make it out of slate or tile but could not find anything that stated it was a UL Listed material. I then decided I would use brick but again nothing stating it was UL Listed except for firebrick. Anyone have any ideas how to build a compliant hearth? What materials to use, how thick it needs to be? Any help is greatly appreciated.

Ed

Please tell us the exact R-value your stove manufacturer requires...only then can you determine what materials and what thicknesses you need......
 
I have been through the entire manual and all it says about floor protection is this:

"This unit will require floor protection if installed on a combustable surface. The minimum floor protection for this unit is 31" x 32" which should give you at least one inch (1") of protection at the rear, 4 inches (4") at each side, and six inches (6") Minimum at the front of the unit."

Then it says the protection should be U.L. approved or equal, the website says the same thing. It does not say anything about R or K values required. Thats why I went with 1" of Durock, I thought I would be safe.

As far as the inspection, there is only a final inspection so they will not want to see how the hearth is constructed. The town says as long as everything is installed by the manufactures specs it will be approved, and they took a copy of the manual. I wonder if they too are now scratching their heads.

I'll event add more layers of Durock and take away a layer of plywood if it will help with the compliance, I do want to raise it up a few inches anyways. Should I put a layer of sheetmetal under the Durock?
 
For your pellet stove all you really need is a good non-combustible hearth built to the dimensions required by the manufacturer. It will not get very hot under the stove. You should be fine and safe. Open up a beer and relax. You've done well.

Though I will agree that Englander could improve their installation manuals. Printing is relatively cheap. And if they want to save more, put better detail information on the web. But hey, this is a bargain stove right?
 
Thanks BeGreen, thats what I thought but I just wanted to be sure. I only want to have to do it once. I'll go with what I have planned now, maybe add 1 more layer of Durock. I didn't think it was going to give off that much heat beneath. Should I add a layer of sheet metal for good measure? What layer would it go in?

BTW already got the beer open, Thanks
 
You can build the Taj Mahal beneath it if it suits your fancy. It's your nickel. But this is not a woodstove.
 
Given that it's a pellet stove, probably it won't matter that much if you use the sheet metal, but if you do it can go under the sandwich, or between any of the layers. The basic idea is that if you have a hot spot on the surface the metal will spread the heat over a much larger area so that you won't have as much in any given area.

If you are wanting a raised hearth, I'd go with the metal 2x4 framing, with a couple layers of durock on top - The only thing I'm not sure on is what the spacing needs to be for the studs under the durock to get enough strength - how does durock compare to plywood?

(Sorry if we were starting to have you overbuild - not all of us recognize model numbers, it helps if your sig says that it's a pellet stove when an outfit is noted for making both...)

Gooserider
 
The Englander 25-PVDC is a pellet model. I was hoping Mike would chime in but he's off to Myrtle Beach.

Ed, contact Englander tech support for peace of mind. My understanding with your stove it that all it needs is a non-combustible barrier underneath it. The manual is vague by just saying "UL approved barrier".
Englander (800) 245-6489

from the manual:
If your floor is constructed of a non-combustible material such as brick or concrete, there is no need for floor protection. If the floor is constructed of a combustible material such as hardwood, linoleum, or carpet, then you will be required to use floor protection between the unit and the combustible. The protection should be U.L. approved or equal, and should be large enough to provide a minimum of one inch (1”) behind and four inches (4”) on both sides of the stove. The clearance in front of the stove should be at least six inches (6”). This freestanding pellet unit will need a minimum 31” x 32” floor protector.
 
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