I'm wondering if someone can tell me what the rear clearance needs to be for a wood burning stove? The new hearth will be built up with 2x4s, plywood, and multiple layers of cement board. The rear wall will be built up the same. Does the rear still need to be 18" from the wall, or can it be closer? The front will have 18" of clearance, and the sides will have 24". Ideally I'd like the rear to be closer to save some living room real estate. Thanks!
Rear clearance for hearth with cement board?
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Not too sure exactly what stove I have. It came with the house. Here is a picture with a serial number.
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Bioburner
Moderator
You have a Earth stove but that's only half the story as the plate does not say what model
Post a picture of the stove proper and someone should be able to ID it so you can track down a owners and installation manual.
Post a picture of the stove proper and someone should be able to ID it so you can track down a owners and installation manual.
The diagram on the back label shows the clearance requirements. That is 36" in all directions from the nearest combustibles back or side. You can reduce the rear or side clearances by using proper wall shielding. 4" of brick will get you down to 24". A properly vented NFPA wall shield will get it down to 12".
https://www.hearth.com/econtent/index.php/articles/stove_wall_clear
https://www.hearth.com/econtent/index.php/articles/stove_wall_clear
Grisu
Minister of Fire
With a new stove you will have close clearances (like 6" in the rear) without any cementboard, potentially ember protection only in the hearth, a nice fireview, better heat output, and a happier home insurance.
If that does not convince you here is the manual for your stove: https://www.hearth.com/images/uploads/Earthstove100_manual.PDF
If that does not convince you here is the manual for your stove: https://www.hearth.com/images/uploads/Earthstove100_manual.PDF
Well I'm thinking 18" in the front, 12" in the back, 18" on each side with 1" of durock underneath and against the wall. 3" of dead air underneath and against the wall. Sound suitable?
No, dead air is not covered by NFPA specs. The rear wall needs to be a ventilated, 1" air gap, open at top and bottom.
Any references of what a 1" air gap looks like? I'm planning on tiling around the whole thing. Is that possible with an air gap?
Sure. It just requires that you leave a 1" gap at the bottom and top of the wall shield so that air can freely flow behind it.
Can anyone provide me with a picture or two of what that looks like? It's hard for me to picture it. Would I cut a 1" hole in my 2x4 framing to vent the air, and tile around it with an exposed hole?
Grisu
Minister of Fire
The link that BeGreen posted has some good schemes in there how to construct a ventilated wall shield. You set the cementboard 1" away from the combustible wall. Screw it with non-combustible spacers into the wall left and right from the stove. Leave a 1" gap at the bottom and leave the top open. After that you can put tile on the cementboard but leave the 1" gaps that air can freely flow behind the wall shield. You can close off the sides. You create a chimney effect where cool air comes in at the bottom and warm air leaves from the top. That air flow will cool the wall that is behind the wall shield.
Maybe this post helps: https://www.hearth.com/talk/threads/in-search-of-wall-shield-ideas.124840/page-3#post-1681671
Maybe this post helps: https://www.hearth.com/talk/threads/in-search-of-wall-shield-ideas.124840/page-3#post-1681671
Okay that is making much more sense. If I shim my floor and wall pad with 1" spacers, say out of plywood, and build it up in the order of: plywood spacers - > 2x4 - > plywood - > 2 or 3 layers durock -> tile, would that be adequate? What would the minimum safe clearance be to the rear wall?
Grisu
Minister of Fire
No, there cannot be anything combustible between the wall shield and the wall. So no plywood or studs etc in the wall shield. The spacers from the wall could be strips of durock or metal studs. You also need only one layer of durock under the tile unless you are concerned that one alone won't hold the weight. Adding several does not change the clearance requirement. Thus:
wall -> non-combustible spacer at least 1" thick -> one or more layers of durock -> tile
Don't forget the air gap at the bottom and the top.
In that case the stove can be as close as 12" from the wall (not the shield) provided your local building inspector and home insurance agree with your installation. They always have final say whether a stove installation is considered safe.
wall -> non-combustible spacer at least 1" thick -> one or more layers of durock -> tile
Don't forget the air gap at the bottom and the top.
In that case the stove can be as close as 12" from the wall (not the shield) provided your local building inspector and home insurance agree with your installation. They always have final say whether a stove installation is considered safe.
What about these other examples?
https://www.hearth.com/talk/threads/can-i-use-wood-studs-to-build-frame-for-hearth-pad.134464/
https://www.hearth.com/talk/threads/can-i-use-wood-studs-to-build-frame-for-hearth-pad.134464/
Grisu
Minister of Fire
A ventilated wall shield is different than a floor protection hearth. For the wall shield you have to follow NFPA 211 guidelines for wall shields. Here is an older version but I don't think that section has changed: https://woodheatstoves.com/free/NFPA211_old.pdf (page 211-38 f)
Please note that if you don't do a ventilated wall shield (like a course of bricks over the wall) then your clearance reduction will be lower.
Please note that if you don't do a ventilated wall shield (like a course of bricks over the wall) then your clearance reduction will be lower.
So for the wall, I could do 1" thick strips of durock between the entire sheet of durock and the existing combustible wall? Allowing ventilation from top to bottom, then tile? Would the same go for my floor, or should I just do metal studs for the floor and wall shield, then durock on top?
Grisu
Minister of Fire
It should approximately look like this: http://i40.photobucket.com/albums/e244/akcooper9/June Dr/2014-02-26180946_zps194da54b.jpg
Same on the bottom with a 1" gap between the hearth and the bottom of the wall shield. Then you could put tile on that cementboard.
For the floor/hearth, I don't know what kind of r-value your stove needs or if it has ever been tested in that regard. If not you may need to follow again NFPA 211 guidelines but ask also your local code authority regarding their requirements and for the current local code. The 2003 NFPA 211 states the following for a stove that has an air space of 2" to 6" underneath:
The air gap is only for a wall. Air needs to be able to freely enter at the bottom of the wall shield (min 1" bottom gap) then travel behind the wall shield (also a 1" gap behind it) then out the top through a 1" gap. You can make your spacers for the wall shield out of long 3" wide strips of 1/2" cement board, doubled up to create the 1" furring shims behind the wall shield. Or you can use ceramic spacers and make the wall shield out of a lighter material like sheet metal. As long as it is totally non-combustible the material doesn't matter. Some folks have used copper or stainless steel. Cement board will be required if the surface is to be tiled.
Leave the floor pad on the floor. No air gap needed there. One generic approved hearth method is to put 4" brick on edge with sheet metal underneath or on top. 4" of brick is R=.80. If you use two sheets of 1/2" Durock NexGen the R value will = .78. Close enough. If you want extra peace of mind you can add another layer. Stagger the seams of the layers of Durock.
Leave the floor pad on the floor. No air gap needed there. One generic approved hearth method is to put 4" brick on edge with sheet metal underneath or on top. 4" of brick is R=.80. If you use two sheets of 1/2" Durock NexGen the R value will = .78. Close enough. If you want extra peace of mind you can add another layer. Stagger the seams of the layers of Durock.
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Copper wall shield example:
https://www.hearth.com/talk/threads/copper-wall-shield-installed.140332/
Nice tiled wallshield example on page 3 of this thread:
https://www.hearth.com/talk/threads/in-search-of-wall-shield-ideas.124840/page-3
https://www.hearth.com/talk/threads/copper-wall-shield-installed.140332/
Nice tiled wallshield example on page 3 of this thread:
https://www.hearth.com/talk/threads/in-search-of-wall-shield-ideas.124840/page-3
Okay so my 2x4 framed pad is okay to stay and layer 2-3 layers of durock on top with the dead air. And for the wall, 1" gap to and bottom, shimmed with durock, with a sheet of durock across the shims acting as my shield. This sound suitable?
Yes, that sounds better. What is the spacing of the 2x4s for the hearth pad? Is there a sheet of plywood on the top under the cement board?
Before hanging the wall shield be sure to account for the thickness of the tile or stone on top of the hearth so that when all is done the wall shield bottom starts 1" above the final hearth pad surface.
Before hanging the wall shield be sure to account for the thickness of the tile or stone on top of the hearth so that when all is done the wall shield bottom starts 1" above the final hearth pad surface.
Copy that. The hearth pad 2x4s are on their side, so 3.5", then plywood, then I'll do 2 layers of durock.
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