Raised hearth construction for basement woodstove installation?

[jcims]

Hi Folks,

We will be installing an Englander 30-NC in our basement in about three weeks and i wanted to set it up on a raised hearth, approx 8-12" above the floor. (New house, poured floor). I would like for the raised area to be adequate for the stove and for accessories, probalby 4'x6' or so. All of the exposed surfaces will likely be stone, with a look not unlike our upstairs hearth, pictured here: http://imgur.com/mVUeO

What do people typically use for the framing of this type of platform? The finished top surface that the stove will be resting on will likely be an inch and a half, if not two inches of stone and mortar, so i'm thinking a (heavy duty) wood frame would be fine, but am not sure. Block seems to be another option, but i have no experience building anything with block.

Any input?

Another thought i have was to place a squirrel cage blower inside the belly of the hearth to pull cold air in from the floor and blow it (gently) up near the stove to help reinforce the natural convection. Thoughts on this? Seems like blowing right on the stove is a bad idea (yes/no?) but mixing in with the really hot air in the vicinity might help even out the temps in the room.

Again, suggestions appreciated!

Thanks

 

[CarbonNeutral]

You need to find the required r-value for the hearth. Stone is a pretty good conductor of heat, so you may be surprised by how little stone contributes.

 

[Backwoods Savage]

We built a raised hearth (16") and love it. We used 2 x 4's but spaced them close together. It is solid. On that we put 1/2" plywood, then cement board, ceramic tile, etc. As stated, it has worked out very well. We especially like it because it raised the fire door high enough so that when sitting on a chair we can load the stove without bending way down to do it.

I don't like the idea of the blower though. You would get much, much better results sitting a small fan in the doorway or hallway and blowing (slow speed on the fan) the cooler air into the warmer room which will have the effect of warming those cooler rooms much better than any other way I've figured out. It sounds backwards; but it works.

 

[CarbonNeutral]

From the manual it looks like you need an r of 1.5. From chimneysweep online you get this table.

For flagstone, or similar, 1"only gives about 0.08, so even 2" wouldn't even get you close. You should probably look to metal tracking and air spaces - I have seen other forum posts about this - don't know much myself

 

[jcims]

You need to find the required r-value for the hearth. Stone is a pretty good conductor of heat, so you may be surprised by how little stone contributes.

Isn't it funny how there's a right way to do everything. Call me a n00b (because I am), but I had no idea that there was such a thing as a consideration of r-values for a hearth. I thought it was just another way to spend money. Thanks for the heads up (all of you) and I'll be doing a bit more research!

I'm liking the 2x4 construction with the 'laminated' top as described. That sounds relatively easy to build and keep level.

 

[ProjectX]

If you have a poured floor i would use cement block (for height) then scratch coat and tile or rock face it no r-values to worry about.

If you use a irregular Natural Stone type product to face imperfections are either not noticed or add a kind of charm to the hearth.


Just my 2 cents


John

 

[Wet1]

I'm liking the 2x4 construction with the 'laminated' top as described. That sounds relatively easy to build and keep level.

Except what Dennis described will not meet your stove requirements. His hearth is basically nothing more than amber protection, which is fine for his application (with his current stove anyway) since that's all that's needed in his case.

If you're going to do this, the easiest/safest way to build would be with noncombustible products. Use concrete block (hollow is a better insulator) or steel studs for the base. Ideally, you don't want to use wood products anywhere. Finish the top off with a layer or two of 1/2" Durock (R.26 each I believe) and then tile or stone over this. Use thinset to bond everything, mortar with the stone if you decide to go that route. If you want even more protection, place a layer of Micore in there as well, but it wont be needed unless you use combustibles in the base.

Good luck.

 

[CarbonNeutral]

Excellent ideas about the concrete blocks - if you do avoid using any wood or combustibles, no need to worry about r-value at all as you are on concrete. Micore is great, but costs some money and isn't that strong. I would just use blocks and maybe cement board (not hardibacker) to level if necessary - thinset all round

 

[ProjectX]

The mind is a terrible thing to waste.

You could build a form with correct height put a zigzag of steel pipe in the form connected so there is one in and one out fill with cement.Then Face with the look you want. Then insert small PC fan in one end of the pipe to blow air through the little pipe maze to circulate.

Hey my screen name is "ProjectX"

Just a idea

 

[Wet1]

LOL, I thought about throwing some Pex in mine (earlier thread), but the general consensus was that there's not enough heat in the heath to bother with a HX. After giving it some more thought and taking some temp readings around the stove, I came to the same conclusion. It's not worth the time, money, and effort.

 

[ProjectX]

Yea but it would give you something to talk about as you chill be the fire plus people that didn't know better would think you a genius lol.

 

[meathead]

Build the face walls first, point them, and let them set up, and then pour the center. Pour to about 1/2" lower than the top of the face walls (so the mortar for the top has some extra grip), and let the center set up. Then mortar on the top pieces - stones/tile/whatever.

Why mix in wood with an otherwise foolproof area to run the stove

Edit - if you don't have a mixer and don't feel like mixing by hand in a wheelbarrow, you can rent one for the weekend at any equipment rental location. Put some tarps down in your work area and work right in the basement right next to the hearth.

 

[CarbonNeutral]

Thinking about it again though, a layer of micore low down in slab could help with losing heat downwards into the ground

 

[meathead]

Thinking about it again though, a layer of micore low down in slab could help with losing heat downwards into the ground

No way - you want as much masonry mass as you can have down there to soak up heat. A 1' thick by 4' x6' hunk of rock will give off a lot of heat, just let it soak it all up

 

[CarbonNeutral]

That's why it's low down - you don't want to be losing that heat to the ground

 

[meathead]

That's why it's low down - you don't want to be losing that heat to the ground

He's just got more cement down there - probably at least 4 more inches under the hearth.

I'd let it soak it up and do its thing, but you can probably apply logic to it either way.

 

[Danno77]

crap, some of you guys will do anything to spend extra money and overthink things. if we're taking votes (and I don't think we are, lol) then count me in for the super cheap and sturdy concrete/cinder blocks with stone top, or if you make a nice full cement block platform then you could just throw tiles straight down on that. Man, that would be cheap and easy like nobody's business. 18 cement blocks at $1.50 (or less) = 27 dollars. nice tiles (16 at <$3) = 48, so you have 75 bucks for the bulk of the install. add another 25 for the tools and grout and whatnot and you've got an 8"+ hearth for 100 bucks.

 

[ProjectX]

If that slab is not insulated under it it will suck the heat right out into the ground. Without insulation the hearth will be a heat sink.

 

[Wet1]

I used 1" of foam at the base of the heart to minimize heat loss/soak to the foundation/earth. Although, I'm going to be insulating the entire floor in my basement as well.

I also see no point in spending all that time and money pouring the entire hearth with solid concrete, blocks are fast and cheap... that's the way I(did) go.

 

[meathead]

I used 1" of foam at the base of the heat to minimize heat loss/soak to the foundation/earth. Although, I'm going to be insulating the entire floor in my basement as well.

I also see no point in spending all that time and money pouring the entire hearth with solid concrete, blocks are fast and cheap... that's the way I(did) go.

Time and money? Guys - it's concrete. $4 to $6 a bag, mix with sand and water and dump in desired location.

If you end up going with blocks, I'd pour them full anyway just for the masonry mass. Seriously, a solid block that large will hold a lot of heat and let it off nice and slow even after the stove is cool.

And if you're going to end up facing the blocks anyway, it will be faster and cheaper to just build walls out of the material you want to face with and then pour the center

 

[Wet1]

I used 1" of foam at the base of the heat to minimize heat loss/soak to the foundation/earth. Although, I'm going to be insulating the entire floor in my basement as well.

I also see no point in spending all that time and money pouring the entire hearth with solid concrete, blocks are fast and cheap... that's the way I(did) go.

Time and money? Guys - it's concrete. $4 to $6 a bag, mix with sand and water and dump in desired location.

If you end up going with blocks, I'd pour them full anyway just for the masonry mass. Seriously, a solid block that large will hold a lot of heat and let it off nice and slow even after the stove is cool.

And if you're going to end up facing the blocks anyway, it will be faster and cheaper to just build walls out of the material you want to face with and then pour the center

Yes, time and money. Don't forget time equals money. Not to mention the time it's going to take for that concrete to dry. Blocks are fast and dirt cheap, and they make solid blocks as well (a 4"x8"x16" block is a whopping $1 at Lowes or HD). I did my large hearth in block for about $30, it took about 10 minutes for this foundation. I see your point with getting the mass to work for you, but only if it's insulated from the slab underneath. As Projectx mentioned, w/o insulation your stored heat will just be going directly to mother earth since solid concrete is a terrible insulator.

Regardless, I think we've given the OP several good options. I have no doubt he'll get the job done right.

 

[Danno77]

I hate mixing cement. For a job that big you'd almost have to rent a mixer. PITA.

 

[meathead]

Yes, time and money. Don't forget time equals money. Not to mention the time it's going to take for that concrete to dry. Blocks are fast and dirt cheap, and they make solid blocks as well (a 4"x8"x16" block is a whopping $1 at Lowes or HD). I did my large hearth in block for about $30, it took about 10 minutes for this foundation. I see your point with getting the mass to work for you, but only if it's insulated from the slab underneath. As Projectx mentioned, w/o insulation your stored heat will just be going directly to mother earth since solid concrete is a terrible insulator.

Regardless, I think we've given the OP several good options. I have no doubt he'll get the job done right.

haha - time equals money at work when you are making money for your time. rushing through a home improvement project does not equal more money in your pocket.

Not that the blocks are rushing it - they are a perfect sollution if you don't want a faced hearth.

To get the dimensions the OP is looking for, he would need to be 3 blocks high, 6 deep, and five (4.5) wide. Total of 90 blocks = $90.00 at the cheapest

Mixed 9 sand to 3 cement, a bag of portland type I/II will fill about 2.6 cubic feet - 10 bags will fill the same cubic footage with 3/4 of a bag left over, and cost about $50 to $60 + $8 for sand. It is a lot more work than the blocks, but if he wants a faced, permanent hearth like the one he said he wanted I think it is the way to go - money and probably even time wise. To rock face a block hearth, you have to buy venir rocks, cement them to the blocks, point everything, then cement a top on. If you build the walls first and then pour, all you have to do is bring some field stone into the basement ( a lot cheaper than venir and it is what imitators are trying to look like with their venirs). Build the walls, point them, throw the remaining field stone into the center making sure it is lower than the walls, and pour over everything.

As far as insulation goes, the more I read the more I realize carbon was right about it. Insulate away, but get as much mass as you can above the insulation.

 

[Danno77]

those cement blocks with the holes in them are 8x8x16, and I thought he said he wanted the hearth 8" to a foot. that's one block tall with a little extra after tile.

 

[meathead]

those cement blocks with the holes in them are 8x8x16, and I thought he said he wanted the hearth 8" to a foot. that's one block tall with a little extra after tile.

Yeah, but you'd have to pour them full to get the mass of the solid blocks or a poured slab.