air space for hearth wall????

[someguy]

I was referred to this site by a post I saw on a tile site I frequent. I plan to build a hearth for my wood stove using 1/2" durarock backing and either ceramic tile or some kind of stone. I was wondering if it is necessary from a code pov to have an air space between the tile backer and the sheetrock. We don't have inspections here and barely any code, but I like to do things as well and saftely as possible.

Thanks for any help.

Ian

 

[Crisnnik]

https://www.hearth.com/econtent/index.php/forums/viewthread/10569/P0/

This is what I did - very similar. The opinions in here should help you out.

 

[begreen]

Ian, welcome. Can you tell us a bit about your stove and what the current clearances are? That will determine how the hearth and the back wall are constructed.

 

[someguy]

I have a steel stove rated to heat 1500 sq ft area. I have the clearances somewhere if you need them but would have to dig them out. Let's just say it gets pretty hot when i crank it up. I want to build the hearth to accommodate this stove, naturally, but eventually probably a bigger one, so clearances would change.

Ian

 

[babalu87]

Need to know the clearances before we could give any solid advice.
The 1" air space behind a non-combustible (IE cement board with/without tile) allows a reduction in clearance to combustibles of , I believe, 50%.
If the clearances of the manufacturer allow 18" to combustibles (a 2X4 sheet rocked wall) then the concrete board on 1" spacers would allow the stove to be 9" from the concrete board.

 

[someguy]

How does closing in the air space vs. having airspace open at the top and bottom effect the clearance requirements.

Ian

 

[babalu87]

It must be open air space on all sides for clearences to be reduced by 50%

 

[someguy]

Is there some kind of vent on the market that could be put in the exposed edges of the airspace to give it a finished look?

Ian

 

[someguy]

How thick would a hearth wall need to be to avoid an air space. (A possible range would help). I know it depends on the stove clearance, but for a biggish stove that required say 18" to the side/back, would double, tripple durarock plus a 3/8" tile get you past an air space requirement? What if you built out from cumbustable a few inches with some metal framing first?

 

[begreen]

Ian, what make & model stove is this? Post a picture if you are not sure.

 

[JimWalshin845]

Welcome Ian,

Forget about code.... remember you want SAFTEY... if you really want SAFETY for you and your family then you will start to look at the codes!

Safe journeys and good luck in your project,
Jim & Kathy

 

[someguy]

My stove is a Century model s273e (the s might be a 5) - Menards about 7 years old. The clearances were on a separate sheet not with the manual and i can't find it at the moment.

 

[someguy]

How does the discance to combustables vary with changes in the width of the air space behind a hearth wall? How does the thichness of the wall effect the distance to combustables? Is there a formula one could use to calculate these variables.

Hoping for help.

Ian

 

[JimWalshin845]

Ian,

This should be your VC manual:

http://www.vermontcastings.com/catalog/elements/files/S19219REV5(E).pdf

Jim & Kathy

 

[begreen]

There is no penalty for exceeding manufacturer's recommended clearances. If you want a margin of safety you can either increase the distance from combustibles by expanding the hearth size and moving ithe stove away from walls or you can add a wall shield that is open at the top and bottom and has a 1" air space behind it.

So far I haven't found the exact manual. I did find one for the Century s274e. Ian, is this very close to your stove model?

http://www.vermontcastings.com/content/products/productdetails.cfm?id=206
clearances s274e:
http://www.vermontcastings.com/catalog/elements/files/S19220REV4E_F_S-0205.pdf

 

[someguy]

Yup, thanks. That looks like my stove. Thanks. Do you know how eliminating the open air space from the hearth wall relates to clearance?

Ian

 

[begreen]

I'm not following the question. I don't think you can reduce the documented factory clearances.

 

[someguy]

I must be having trouble with wood stove speak or something..... sorry for the confusion. I'll try again. I don't like the idea of an open air space for astetic reasons, first of all. I understand it's function.

So that said I want to build a hearth wall that complies with mfg clearances but without an open air space around the hearth, so I'm thinking if I make the hearth wall thicker while eliminating the open ends there should be a formula to accomplish that. I can still leave a space between combustables I just don't want to have a gap on visible edges especially. Does that make any more sense. I am a construction guy for the past 20 years I should be able to make myself understood, but every area has it's own language.

Bye the bye I would be ok with some kind of grilled vent on the open space it anyone makes such a thing.

Hope this makes more sense.

 

[Crisnnik]

This is how I accomlished it. There is a one inch airspace on the top, bottom, sides, and behind the wall tile/Durock. I trimmed the edges to hide the raw ends of the tile and cement board, but left the airspace. After painting the wall, you hardly notice it at all. Even my wife who was against it for aesthetic reasons is pleased with the result. It is my understanding from threads on the forum that a wall must comply to this standard in order to be nfpa approved.

 

[begreen]

What may be confusing is that many stoves provide two options for clearances to combustibles. One table is for an unprotected wall and the other table is for a protected wall. In your stove's case there is only one clearances table provided.

Sorry, if I get this wrong, but it appears that the concern is whether it is mandatory to have a heat-shielded wall with a 1" air gap behind it. Is that the correct? If so, relax, this is not required as long as you meet or exceed the manufacturer's recommended clearance to combustibles. There is no need to add the extra 1" gap behind the heat shield, unless you are trying to reduce clearances as per the manufacturer's tables.

In your case, increase the distance from the wall to the stove beyond the stove specified distances if you want to add an additional margin of safety.

 

[someguy]

Sorry, if I get this wrong, but it appears that the concern is whether it is mandatory to have a heat-shielded wall with a 1” air gap behind it. Is that the correct? If so, relax, this is not required as long as you meet or exceed the manufacturer’s recommended clearance to combustibles.

This wasn't my concern. I just wanted to get the stove a close to the wall as possible within safety margins. I like the previous post with the picture, that solves my problem about the air space, thanks.

One concern I have in additon the the others stated is that even though my stove currently exceeds the clearance to combustables on an unprotected wall, one wall closest to the stove in back does get very hot when the stove is cranked up. Too hot to keep your hand on. This is a little worrisome, but I assume that it is not a problem as long as my clearance is ok. Am I right is this assumption?

 

[JimWalshin845]

Ian,

I am not sure what you are relating to? The specs are clear and if you want combustibles closer than what is recommended or what meets code then you are probably looking/barking up the wrong tree.

Please be more specific.

Thanks