Question on wood stove clearance without airspace behind wall shield

[eikeland]

My Vermont Castings Encore is being delivered today, and I am a little confused about the minimum clearance required for what I had planned to do. The manual of the stove lists the minimum clearances to combustibles with and without wall shields. However, all the wall shields are listed as having a 1" air space behind it. I was hoping I could use 3/4 Micore 300 (R-value=1.545) with 1.5" stone on top of that without using the airspace. However, I am not sure if that will meet code. I also checked NFPA 211 and table 13.6.2.1 has a clearance reduction chart. However, it just lists some examples without showing how it was calculated and what the R value is. (b) in the table lists 1/2 insulation board with 1" glass fiber without airspace, but doesn't list the R-value of it so I cannot really compare it. Section 13.6.2.7 says I can use insulation material that has a thermal conductivity of 1.0Btu-in/hr-ft2-F or less. This value is the inverse of an R value, so that should give me a value of 1/1.545=0.647. However, it doesn't say how much I can reduce it by. I haven't found any other references to clearances to combustibles without using airspace. Since my living room is kind of small, I'd like to keep it as close as possible to the wall while still meeting code (obviously). Can someone help me out with what I need or point me in the right direction with respect to minimum clearance without air space?
Thanks

 

[begreen]

Micore is not a good substrate, you want to use cement board. The air gap is necessary for a proper NFPA 211 wall shield. Using it you can reduce the back and side clearances to 12" Which model # Encore is this?

 

[eikeland]

Can you explain why a cement board is better than Micore 300 (I would be using one of those metal grids on top of it so that thinset would stick)? Would you recommend 1/2" Durock instead? Hearths don't have a airspace in them, so you would think if you could reproduce the thermal resistance of a hearth that meets code if you also install a rear heat shield (the stove has a bottom shield) and thereby reduce the clearance.
It's the 2040 (Classic Black) model.

 

[begreen]

"Clearances may be reduced only by means approved by the regulatory authority, and in accordance with the clearances listed in this manual."

Most of the heat is radiated from the side, front, back and top. There is only one tested and approved form of wall shield, that is NFPA 211. It is an industry tested and accepted standard. This will be recognized by the inspector. The 2040 manual very clearly illustrates how to make the wall shield. Cement board will provide a much more solid backer. It is designed for this purpose. Micore is soft and fibrous. An easy way to make a wall shield is to snap off long 3" wide strips from the cement board. Double them up on each stud to create 1" spacers. The manual lists the accepted clearance reductions under the Protected Surfaces column. The lowest rear clearance with a, top exit, double-wall pipe with vertical flue shield in place and an approved wall shield is 5" which is remarkable for this stove. Remember that 5" is from the combustible surface, which is the wall behind the ventilated wall shield. If you build an approved wall shield and it projects say 2" from the wall the stove clearance to the stone will be only 3", 5" to the drywall behind the shield.

 

[eikeland]

The reason why I would like to use Micore is that it has more than twice the R value of Durock for the same thickness and I used this to make a Hearth that was thinner than that I could have made out of Durock. I know the manual is pretty good at explaining how to make a wall shield and so is NFPA 211, but I was hoping I did not have to have the air gap. It doesn't make that much of a difference though since the distance is to the combustible and not the stone veneer so I should be OK. However, since this is a new addition I didn't put sheetrock on part of the back wall, but that's not a big deal to add this.
I also plan to talk to the local inspector before I make the stone veneer to make sure there are no other building codes that I need to be aware of.

 

[begreen]

The ventilated air space is what is doing the work. It is constantly convecting away the heat. No need for sheet rock behind the wall shield. Actually, you could build the wall right down to the floor if you have clear access top and bottom to the wall cavity on the other side of the wall. Stud width 2x14" vents could be installed at the top and bottom of the stud cavity to vent it. Be sure your inspector agrees, but that should work ok. The main thing is that the grilles never be blocked by furniture or appliances.