13-nc R2 hearth pad

[cjgaughan]

Hi all, first off, great forum! Very informative.

I've done some searching on this and have an idea, but just had a more specific question.


I just picked up this wood stove for my camp (or cottage or cabin, whatever you call it!). It is replacing an older Heritage woodstove that, although certified, was installed completely wrong.

I will be installing it on a combustible surface, so from my understanding I need some kind of hearth pad to the proper dimensions with an R value of 2. I'd like to keep this as simple/cheap as possible, so I was wondering if I could do the following:

4" cinder blocks to create a "frame", on top of which I would place a piece of sheet metal or durock and then either paver stones or some other kind of material. Simple, easy to do, and I have most of the materials already. Might not look too pretty but it is a camp after all. Would this be acceptable? The stove is on a pedestal so the weight is more spread out also.

I've found different R values for both the cinder blocks and airspace... if I create a "frame" or "studs" with the cinder blocks, would that 4" count as airspace or as cinderblocks?

Also on a side note, new stove has 6" flue size, existing chimney is 7". Will that be an issue either with operation or inspection?

Thanks for any input it's much appreciated.

 

[begreen]

Welcome. Sounds like it would be adequate. You might want to make a frame around the base of the blocks to keep them from moving over time. Also, you'll want a solid base under the Durock to support the stove weight. Make sure there is at least a flat face of the block centered under the all edges of the pedestal.

7" may work ok if the chimney is tall enough. Is the chimney straight up from the stove or out the wall and then up? How tall is the chimney?

PS: What kind of hearth was the Heritage on? Was it at least an R=1.2 hearth? I was wondering if this could be built up with a couple layers of Durock NexGen to achieve the R=2.0 requirement. That might be simpler.

 

[Jags]

Yeah - as BG was pointing to...the Durock really doesn't have much for structural strength. It will need to be fairly well supported to hold the weight of a stove.

 

[cjgaughan]

The heritage was raised off the laminate floor with some bricks and wooden shims (i said wrong! Haha). No ember pad or anything.

But if i made "studs" with the bricks or even staggerred them, would an inspector count the space as air space?

Also, chimney is straight up, single story peak roof, comes out at the peak or very close. So probably 15' or so of chimney

 

[begreen]

Sounds like it was under-insulated for the Heritage. Regular brick laid on edge (4" thick) will have an R value of .8.

Concrete doesn't have much insulation value. The air space should qualify, but that is up to the inspector. As an alternative you could put 3 layers of Durock NexGen on the bricks on edge.

The chimney is going to be close. It may work out ok but it may need an extra couple feet added to draw well. It's worth a try at least.

 

[cjgaughan]

Currently in the process of setting this up. Not sure im' going to like a 48x48 raised hearth in the middle of the main living area, but that's my plan for now.

Just for brainstorming sakes, does the R2 have to apply for the entire hearth pad, or just directly under the stove? I.e. Could I have the stove raised on a smaller raised section that would be R2, then continue around this at more "floor" height with an ember pad to achieve the required dimensions of the floor protection? Would the raised stove help with this?

I like the idea of raising the stove just not necessarily a 48x48" raised platform.

 

[begreen]

The R=2.0 rating applies to the entire hearth pad. The drop in height would help reduce heat radiated in front of the stove, but there is no spec on that to show the inspector or insurance co..

 

[cjgaughan]

Thats kind of what i figured.

What about having the stove raised where it sits, then using different materials around /in front that would still obtain R2 but with much less thickness? If i go right to the subfloor or even joists I may be able to get it to R2 with relatively little height. Do inspectors not like this "mix" either?

I guess i could create the entire pad to R2 in this fashion then raise the stove itself with bricks or something of the like non combustible.

 

[begreen]

R2 is R2. I don't see why doing it with different methods would matter as long as the coverage meets the manual's hearth requirements. However, remember that most good insulation board, like micore is a very poor substrate. It's too soft and porous and needs 1/2" cement board on top for a decent tile base.