Determining clearance reduction when the manual just refers to code

[begreen]

Jaquith asked "can you tell me how we could reduce clearances for these stoves by adding a NSPA 2111 Heat Sheild to the combustible wall behind the stove?"

I ran into this late this week when looking into the Harman Oakwood for a corner installation. I'd like to calculate what the sidewall clearances would be reduced to if there I install a non-combustible wall shield. Also helpful would be knowing how high above the stove it has to be and does it need to continue to the ceiling if there is a double-wall stove pipe. It would be great if Harman did the work for the customer, but they don't. The manual refers to NFPA 211 code instead of providing this information. Sounds like it would be a great, short Wiki item if someone could post it.

 

[Shane]

I don't have my code book with me so I'll give you a short answer.
NFPA211 allows clearance reduction of up to 66%, when using a properly constructed wall heat shield. They have a table listing acceptable materials, required thickness etc. The shield has to be space 1" off of the wall and supported with non-combustible heat shield spacers. Those spacers can only be installed on the perimieter of the heat shield (not directly behind the stove) to prevent possible heat transfer through fasteners. The heat shield has to be open on the top and bottom or the sides and to to allow for proper air circulation.
Here's the catch though. The code is based on 36" appliance clearances. And if memory serves there is a paragraph stating that the clearances shall not be reduced below 12". Once again I don't have my code book at home, so I'll verify on Monday and quote it verbatim.

 

[begreen]

Thanks Shane. Our old installation had said spacing and was open top and bottom. I'd do the same if I go with the Oakwood. However, I swear I saw somewhere, a diagram that showed using two layers of Durock strips as the 1" spacers. These were applied to each stud (16" centers) including behind the stove. Then the surface was tiled. It sounds like this is wrong according to code. If I find the reference, I'll post it.

 

[BrotherBart]

The current working document is available here. Ya just can't print it of download it.

http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=211

 

[begreen]

The document I was looking for is posted on USG's site. It's Durock submittal sheet CB198.
http://tinyurl.com/nmmt3

BB, I get a link to the document, but it's not viewable. Maybe that's just for members?

 

[BrotherBart]

The document I was looking for is posted on USG's site. It's Durock submittal sheet CB198.
http://tinyurl.com/nmmt3

BB, I get a link to the document, but it's not viewable. Maybe that's just for members?

Can't be so. I am sitting here reading it. Go down to the preview the document link at the bottom of the page.

 

[Shane]

I can read it, go to 211-40, 211-41, 211-42.

 

[begreen]

Thank you! I missed the link for previewing at the bottom of the page. Reading up now.

 

[begreen]

So the recommendation to not use spacers behind the appliance seems almost impossible with a corner installation. There has to be some support for the heat shield in the corner. The code book shows using a conducting metal like washers or metal pipe as a spacer. It seems there is a better way.

I want a safe installation, but think that if I follow Durock's recommendation of "not" using a heat conducting spacer, but instead create a 1" furring strips out of 2 layers of Durrock strips, that I would be safe and compliant. The only heat conductor would be the screw embedded in the Durock and tiled over. Elk, would you pass inspection on such an installation?

 

[Shane]

The screw is the area of concern. The shield will extend down to 1" above the hearth and extend x amount of inches above the hearth. For corner support install the spacers in these areas above and below the actual firebox. You will still support your shield properly and won't have any connectors directly behind the firebox.

 

[MountainStoveGuy]

Bgree, what about the ceramic spacers that imperial manufacturing sells?

 

[Jaquith]

I don't have my code book with me so I'll give you a short answer.
NFPA211 allows clearance reduction of up to 66%, when using a properly constructed wall heat shield...Here's the catch though. The code is based on 36" appliance clearances. And if memory serves there is a paragraph stating that the clearances shall not be reduced below 12". Once again I don't have my code book at home, so I'll verify on Monday and quote it verbatim.

It appears (according to the downloaded HS manual) that you can reduce clearances at least for some of the HS stoves. I have read the manual and it does give you reduced clearances for 2 of the 3 stove manuals I read. If I am reading the manual right that is.

"The code is based on 36" appliance clearances." can you explained that please?

Jaquith

 

[Shane]

What I meant by the code is based on 36" clearances is that the default NFPA211 clearance to combustibles is 36". If hearthstone states that you can have a clearance under 12" then you can. But if a stove company say had a 22" clearance on their stove and that was the only manufacturer listed clearance and they recommended that you use the NFPA211 clearance reduction then you wouldn't be able to go under 12"

 

[begreen]

Bgree, what about the ceramic spacers that imperial manufacturing sells?

They'd work too, but they still need a screw in the center. I like using durock as the spacer because the material is inexpensive and already on the job as the wall shield tile backing board.

I am amazed that code is worried about the heat transmission of a screw. Has there been a single documented case of wall heat shield failure due to heat transmission of a screw holding up the heat shield? I will ask our inspector what he thinks.

 

[MountainStoveGuy]

I would have a hard time believing a screw can burn a house down, (in this application) now there is a idea on how to transfer heat to other rooms. I can see it now, the living room backs up to the bed room, the bedroom is on the same wall as the stove. you run some extra long screws through the wall and wa laa! your bedroom is heated! SWEET. :cheese: (and silent too, unlike vents!)

 

[begreen]

LOL I can see me explaining that to my wife. Honey, I'm gonna put a few, extra big screws behind the stove so that the bedroom is nice an toasty.

Her - yeh, sure. wishful thinking -

 

[elkimmeg]

Begreen sorry out of town the past few days Pittsburg. I have diagrams detailing where screws and spacers can be installed.
ITs not as impossible. Remember they can not be situated directly behind the fire box but can be located below and above the stove but not in the middle behind the fire box and hottest position. Many use 1" 3/8" copper pipe for spacers. The maxium you can reduce a proper reduced clearance suround is 12" There are two factors here the actual stove and satisfying the connector pipe requirements. Double wall pipe can be installed or single wall with a shield. Even if the stove sits 12" away and you use single wall pipe the clearance is now the 18" or the single wall pipe. Use double wall pipe and the stove clearance is 12" and the manufactures specs of the double wall connector pipe ,6" like I said you have to address two issues the stove placement and the connector pipe clearances

 

[begreen]

OK, I can see how to do that using strips of durock or wonderboard as well. I'm kind of bummed out because we were leaning towards the Jotul Oslo, but now find out that one can't use the side door in a corner installation. Not sure what we're going to do now. I guess we could move the stove over to gain clearance on the door side. Or we are back to the Oakwood or PE Classic. I'll try to figure code calculations in for this stove with a wall shield, but what a PITA. It would be soooo much easier if Harman provided this info. I don't really want to discuss this to death with the new-on-the-job building inspector.

 

[MountainStoveGuy]

why cant you use the side load in the corner? because of the side door hearth requirments? is it a lack of space? i know you are battleing a window problem.

 

[elkimmeg]

What about a top and front load stove? if side load will not comply with clearances? What if I can fax you the NFPA code or International Mechanical codes, which depicts the proper installation requirements Submitt them with your installation permit application then when p=ush comes to shove refer to them that their dept approved the installation and you built according to the approved plans

 

[begreen]

why cant you use the side load in the corner? because of the side door hearth requirments? is it a lack of space? i know you are battleing a window problem.

The Oslo manual says that one must have the side door locked shut for corner installations. Sadly, it is either not use the side door due to the window sill on the left side or move the stove much further to the right, into the room, thus giving up desirable floor space.

 

[MountainStoveGuy]

news to me, i will have to check out the new manual. Last years model stated that as long as you had 16" clearance on the left, and 6 on the right you were ok. Thanks for the heads up. Heck i didnt even know that they offerd a lock for the side load. Side loads are overrated any way.. LOL

 

[begreen]

What about a top and front load stove? if side load will not comply with clearances? What if I can fax you the NFPA code or International Mechanical codes, which depicts the proper installation requirements Submitt them with your installation permit application then when p=ush comes to shove refer to them that their dept approved the installation and you built according to the approved plans

I like top-loaders. We went over the Encore, but we are going with a 6" flue and the installer said they have had two installations where there was a small problem with smoke coming out from the top load with the 6" flue. He is expecting to have at least one offset (pair of 30's) which will slightly reduce draft even more. So, I'd rather get a stove that is designed for the 6" flue from the get go. But, the Harman Oakwood is still in consideration. Also considering the Hearthstone Phoenix and the PE Spectrum Classic. The Classic presents the least installation issues with its tight clearances and seems to have a near legendary reputation on this site, so it is a strong contender.

 

[begreen]

news to me, i will have to check out the new manual. Last years model stated that as long as you had 16" clearance on the left, and 6 on the right you were ok. Thanks for the heads up. Heck i didnt even know that they offerd a lock for the side load. Side loads are overrated any way.. LOL

It's in the technical info, page 38:
4.3 Walls
Note! The side load door must not be used in corner installations.

Locking is also mentioned for reduced hearthpads and for all alcove installs:
Alternate hearth protection
A hearth pad measuring 46”wide X 50,5” deep
(1168mmx1283mm)can be used only if the left side door is looked (sic)
to prevent use.

 

[begreen]

What about a top and front load stove? if side load will not comply with clearances? What if I can fax you the NFPA code or International Mechanical codes, which depicts the proper installation requirements Submitt them with your installation permit application then when p=ush comes to shove refer to them that their dept approved the installation and you built according to the approved plans

Thanks Elk. Unfortunately if the inspector says 'I don't think so', the building dept. is happy to discuss this to death with you @ $118/hr. We're trying not to get involved with a hassle here and would rather the installer had a clearly documented case from the stove manufacturer to make this a simple and quick inspection.