horse hair plaster
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Yeah, it doesn't matter much, as Doug said, what matters is what's behind it. Even modern drywall construction is considered combustible because of the wooden studs directly behind. Neither the drywall nor your plaster does diddly squat to insulate the wood behind from the heat of a wood burning appliance (if that's the application you had in mind). Rick
At least ya know it doesn't have asbestos in it if it has horse hair. The lath is really cumbustable but it is mostly buried in plaster.
buried in plaster or not it can still burn and there is not enough r value in that plaster to make any difference in heat transfer
Grisu
Minister of Fire
Just wondering: How much R-value would someone need? Plaster board has .45 per half inch. At 2" that's R1.8.
Yeah that may be true but we are not talking about plaster board and horse hair plaster is only about 1/2" thick not 2". So even if it is.45 that is not enough to reduce clearance at all.
Grisu
Minister of Fire
The 2" thickness is from the OP:
But I agree that someone should not assume horse hair plaster has the same r-value as plaster board. Still, in a more general sense, what kind of r-value would be considered sufficient? How many layers of brick for example someone would need?
sorry I missed that but I would also not assume that it is 2" every where else either I think that the right solution is to assume that the wall is considered combustible. As far as what r value is needed I will have to look I know that 1 brick directly over combustibles is a 1/3 reduction.
You need to post a picture and a better description of what you are trying to do It may not be an issue at all but with out seeing it it is hard to say.
https://www.hearth.com/talk/threads/new-member-old-house.127082/ this is my introduction post. You can see in pics where I chipped away the plaster. I'm planning on filling the space between the mantle and the wall with bricks. I'll see about getting some better pics.
Mantle is painted stone, I think marble. The hearth is stone about an inch thick. I don't know if it's slate or marble. It's all sand underneath. the narrow piece of stone for the mantle has what I've heard called a hearth extension. 
I dug out the back since it was loose ruble. It's about 16" deep till I hit the arch in the basement.
I dug out the back since it was loose ruble. It's about 16" deep till I hit the arch in the basement.
Grisu
Minister of Fire
I could lay the bricks two deep in the space. I'm concerned that since the bricks will retain heat that I would actually be reducing clearance since the bricks would be closer to the plaster.
How about just putting a heat shield in there? Leave a 1" gap in the bottom and another gap in the top. That should reduce your clearances the most. If you leave the mantel intact, the shield will hardly be visible from the front. And if you want you can put one layer of bricks or maybe something simpler like durock in first (or just leave the plaster), then an air gap of at least 1" and then the shield.
How far do you actually want to recess the Jotul into the fireplace? Any plans on using the side-loading feature?
ailanthus
Feeling the Heat
I have no knowledge, but good luck. A jotul in that spot will make one of the best looking installations ever. I love old houses.
Grisu, by heat shield do you mean just stock sheet metal? I was thinking of stuffing some mineral wool in and then installing the brick work. I know a mason so the brick work won't be a problem. Safety takes priority. I'd like to have the stove stick out 8" which means I won't be able to use the side door and I'd have to use the rear exit option. I could push the stove all the way back and use the top exit option but I wouldn't think the heat will radiate as well. I'm also planning on extending the hearth.
Alenthus, thanks, this was my grandfather's house so it means a lot to me.
Alenthus, thanks, this was my grandfather's house so it means a lot to me.
kennyp2339
Minister of Fire
I have a similar situation at a friends house, we are going to tare the mantel down and make the fireplace opening flush to his existing walls. The problem at his house is that last year we took out his little wood burning insert, and replaced it with a NC-30 free standing, the installed went great but this winter we found out that the stove (radiant type) needs to be more exposed to free moving air, so the idea is to rip the mantel down, we should gain about 16 extra inches on the sides of the stove. At the same time we do that I'm gona try another idea and insulate the fire box with rock wool then install cement board over it to keep heat from being absorbed into the natural stone fire box, also going to create a block off plate and insulate the chimney. I will take pictures and create a new thread
Grisu
Minister of Fire
There are several ways you can build a heat shield but sheet metal is the most common one. What is important is to leave a 1" gap from the wall and the floor that air can freely flow behind it. That will vastly reduce the heat the combustible material (lath in your case) will be exposed to. Here is a link: http://www.woodheat.org/clearances.html
See if those reductions would be enough to meet clearances to the mantel as stated in the manual for fireplace installations. Your idea may also work but there are more code knowledgeable members here than me. However, the idea of mineral wool and then Roxul would maybe be something to do in the back of the fireplace. It looks from your first pictures that it sits on an exterior wall. Thus, some added insulation may not be a bad idea to reduce heat loss from the back of the fireplace. You also know about a block-off plate?
Have you checked what people say here about loading the Jotul from the front? I vaguely remember people really prefer the side loading option. Here is a thread: https://www.hearth.com/talk/threads/my-jotul-will-have-to-be-front-load-only.113621/ The Jotul F55 is a dedicated front loader and may be easier in that regard. You could also look at Hearthstone stoves like the Manchester.
And I agree with Ailanthus: That looks like a great home. A nice cast-iron (or maybe soapstone?) stove will look great in the fireplace.
kennyp, I was going to try to keep the stove recessed into the fireplace thinking it would be best to have it sitting on as much of the hearth as much as possible and to have a straight shot up the chimney. After reading your post I'm thinking I should let it stick out as much as possible. Do you agree?
Grisu, I'll look into the heat shield idea, I have an appointment with an installer next week I'll be batting ideas around with him. I am familiar with block off plates. I checked out the link to the post you added I am considering letting the stove stick out just far enough, about 16", to use the side door plus to let the heat circulate. That will require extending the hearth out farther and wider. I don't mind the extra work, I think I'll be glad I did it when it's done. The 55 is to big to fit. I was originally thinking about the Greenville 45, After a trip back to the stove shop I realized the Oslo would fit. Since it's a larger stove I'd like to make it work. This is a big old house with high ceilings and drafty windows, the room also leads to the main hall with the large stair case. I did look at most of the big name manufacturers, most just won't fit right in the opening. I've really have my heart set on Jotul. They have the right look, detentions, and reputation I'm looking for. I made some boxes out of plywood to get a better idea of how they would fit.
Oslo 16" out.
Oslo set deep.
Greenville 16" out.
Greenville set deep.
Grisu, I'll look into the heat shield idea, I have an appointment with an installer next week I'll be batting ideas around with him. I am familiar with block off plates. I checked out the link to the post you added I am considering letting the stove stick out just far enough, about 16", to use the side door plus to let the heat circulate. That will require extending the hearth out farther and wider. I don't mind the extra work, I think I'll be glad I did it when it's done. The 55 is to big to fit. I was originally thinking about the Greenville 45, After a trip back to the stove shop I realized the Oslo would fit. Since it's a larger stove I'd like to make it work. This is a big old house with high ceilings and drafty windows, the room also leads to the main hall with the large stair case. I did look at most of the big name manufacturers, most just won't fit right in the opening. I've really have my heart set on Jotul. They have the right look, detentions, and reputation I'm looking for. I made some boxes out of plywood to get a better idea of how they would fit.
Oslo 16" out.
Oslo set deep.
Greenville 16" out.
Greenville set deep.
Grisu
Minister of Fire
I did not know that the Oslo would fit in there that tight. The manual states 11" to side trim which in your case I would assume is the lath under the plaster. It does not look like you have that and there is no provision for a heat shield. For an alcove install with heat shield it says 6" and even that may be too close in your case. Since the heat shield would also be within the fireplace it may be less effective so I would assume less reduction just to be safe. Moreover, I would be worried if your mantel will withstand the heat over time being so close to the stovetop even when it is non-combustible. Good that you will get your installer over to check things out. I would also think about sending some pics over to Jotul and ask for their opinion.
I would be concerned with the Oslo going thermonuclear with that tight of spacing. Even if somehow you could meet the C to C clearances I don't see how you could move enough air around that stove to keep it from overheating.
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