Author Topic: insulation behind wood stove  (Read 11671 times)

0 Members and 1 Guest are viewing this topic.

Offline CWhite

  • Full Member
  • ***
  • Posts: 160
  • CountryPlans member
    • The Funky Chicken Art Project
insulation behind wood stove
« on: January 22, 2008, 07:55:55 AM »
Hi there,

I am trying to plan ahead for the rock face I want to put behind my woodstove.  The stove will be located tucked into the L shape of the staircase, and there is already a triple wall constructed through the upstairs floor and up through the roof.  The floor under the stove is concrete, so no worries there. 
My question is, how to make sure the stove heat doesn't translate to the wall behind it?  It will be positioned a bit more than code requires due to the fact that the stove pipe comes out the back of the stove instead of the top, but even so, I want to do the proper layers of stuff to make it right.  I have a memory of needed an inch air space behind a rock board of some kind that I then, adhere the stacked stone in front of. 
How do you space the rock board one inch from the wall?   
Thanks if anyone can advise.
Christina

Offline MountainDon

  • Administrator
  • Journeyman
  • *****
  • Posts: 15,793
  • Gender: Male
  • Jemez Mountains, NM; that's pronounced HEY-mess
    • My 15.75 x 30 Jemez Cabin
Re: insulation behind wood stove
« Reply #1 on: January 22, 2008, 11:09:24 AM »
Do you have the stove manufacturers clearance list? UL approved stoves should come with the minimum clearance specs. Usually there are two figures given for side and rear clearances. The distance from stove to unprotected  surfaces and the distance to protected surfaces.

For example the stove I'm going to use, Vermont Castings Aspen...

            unprotected surfaces         protected surfaces
sides               24"                                   16"
REAR               13"                                    9"

The clearances for a stove with a rear smoke pipe exit can be different (greater) than for a top exit. Once again full info should be supplied by the stove manufacturer. There are also clearance minimums for the space above a stove, as well as under the stove. From my experience the inspectors give no leeway at all in these measurements. And if they did, and/or you cheated, and had a fire, the insurance adjuster could refuse any claims.

By protected surface they mean a non combustible product (metal, stone, etc.) that is spaced away from the combustible wall behind with a 1" air space. Everything about that surface must be non combustible. Drywall does not count as non-combustible because of the paper layers, for example. When using a protection system like this the reduced clearance measurement is taken from the stove to the combustible surface behind the shield, not to any surface of the shielding product. There must be an air space under this protection for air to enter the space behind. As well there must be a free exit space at the upper edge.

The spacing is usually done with ceramic or metal tube just large enough for the screws used to mount the protection. Mounting hardware should not be installed directly in line with the stove itself, but to towards the front, rear or outer sides.

Some stoves have heat shield kits available for them from the manufacturer. In the example of the VC Aspen the use of a rear heat shield on the stove, reduces the non-protected wall clearance to 11" from 13". There is no further reduction if a protected wall is used.

So, if you have the required clearances for your stove's listed figures, stove to finished wall, you don't need to have an air spaced system. It would not hurt, but is not listed as necessary.

I have read that when using stone or brick materials mortared to a combustible surface the clearance measurement must be taken from the stove to the stone surface closest to the stove, not from the combustible substrate behind the stone.

Just because something has been done and has not failed, doesnt mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline Redoverfarm

  • Journeyman
  • *****
  • Posts: 6,302
  • Gender: Male
  • Applachian Mtns, West Virginia
Re: insulation behind wood stove
« Reply #2 on: January 22, 2008, 12:30:48 PM »
Christine IMO and what I have done in the past works really well.  Using 1/2-3/4" plywood screwed to the studs. This is followed by Metal Lath which is nailed in place to prevent buckling.  Then  parge that lath surface with 3/8-1/2" mortar parging.  Then come back in 3-5 days and apply your mason product whether it be cultured stone, brick veneer.

This will also give you some added heat when the stove heats up the mason product and you will get some thermal mass.

If you are concerned then still use the manufacturers recommendations for clearence to the rock face.  This is a pretty fun project if working with veneer stone as you can customize the way "you" want it to look.

Offline glenn kangiser

  • The Troglodyte
  • Administrator
  • Journeyman
  • *****
  • Posts: 24,686
  • Gender: Male
  • Central California Sierras- Home of Yosemite NP
    • Underground Cabin
Re: insulation behind wood stove
« Reply #3 on: January 22, 2008, 02:25:57 PM »
My mom and dad had a brick chimney in the house and when they tore it out, the wood contacting it was charred.  It had nearly started a fire, so if under the manufacturers spec I would still use the air space to combustibles or even sheetrock on studs.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

Offline CWhite

  • Full Member
  • ***
  • Posts: 160
  • CountryPlans member
    • The Funky Chicken Art Project
Re: insulation behind wood stove
« Reply #4 on: January 22, 2008, 02:51:02 PM »
Ok, thanks for the responses.  I have every intention of using a 1" airspace, but didn't know how to create it.  You have given me 2 viable ways to accomplish it.  I also intend on using a contact board that is flame proof behind a built up stone wall.  We have left plenty of room where it will be.  I just didn't know how to do it.

Thanks again.  I can quit worrying about that now.  On to gutters....and muddy pathsways, and sheetrock. 
Christina

Offline Willy

  • Senior Member
  • ****
  • Posts: 562
  • Gender: Male
  • Fighting Wildland Fires for a Living! Okanogan, WA
Re: insulation behind wood stove
« Reply #5 on: January 22, 2008, 02:59:47 PM »
Ok, thanks for the responses.  I have every intention of using a 1" airspace, but didn't know how to create it.  You have given me 2 viable ways to accomplish it.  I also intend on using a contact board that is flame proof behind a built up stone wall.  We have left plenty of room where it will be.  I just didn't know how to do it.

Thanks again.  I can quit worrying about that now.  On to gutters....and muddy pathsways, and sheetrock. 
Christina
Go with triple wall insulated stack all the way. You can cut clearences way down and still get heat off it. Single wall stack will get RED HOT FAST! It cost more but you can sleep better at night knowing that if you left the damper out a little your stack is not getting red hot! It is easy over the year to miss a damper once in a while as I have done it 2-3 times in 20 years and would have had a fire because of it. One time the top of my stove was red hot but the stack was OK. Don't cut corners on your stack to save money it could cost you your life some day. PS I have never faenll asleep with the damper out but many times got up and double checked it was in all the way!! Mark
« Last Edit: January 22, 2008, 03:39:48 PM by Willy »

Offline Redoverfarm

  • Journeyman
  • *****
  • Posts: 6,302
  • Gender: Male
  • Applachian Mtns, West Virginia
Re: insulation behind wood stove
« Reply #6 on: January 22, 2008, 03:10:19 PM »
Christina if you were up this way you wouldn't have to worry about the mud. It's all frozen.  When I moved in my house the winter caught me. I had to wait until spring to get grass sowed and get rid of the mud.  Just lay down some straw and 2X to walk on and forget it.

Offline Redoverfarm

  • Journeyman
  • *****
  • Posts: 6,302
  • Gender: Male
  • Applachian Mtns, West Virginia
Re: insulation behind wood stove
« Reply #7 on: January 22, 2008, 04:05:33 PM »
Christina you got my curiosity up. I checked the clearences on my Hearthstone stove which is a 80,000 BTU. It is 29" from the flue(top draft model) to wall and 20" from the stove wall to house wall set 45 deg angle in the corner. Standard 90 deg it is 12" flue to wall and 11" stove back to wall.  I think I have about 10" in back and 6" to partial side but all of mine is Mason constructed with cultured stone.

Offline MountainDon

  • Administrator
  • Journeyman
  • *****
  • Posts: 15,793
  • Gender: Male
  • Jemez Mountains, NM; that's pronounced HEY-mess
    • My 15.75 x 30 Jemez Cabin
Re: insulation behind wood stove
« Reply #8 on: January 22, 2008, 04:15:46 PM »
Re: what Glenn said...

Over time the character of the wood can be changed by extended exposure to heat.

Temperature        Time (days)        Condition
107C   224F           1050                light chocolate color
120C   248F           1235                brittle, dark-chocolate color
140C   284F           320                  lost 45% of weight, became like charcoal
150C   302F           165                  lost 65% of weight, became like charcoal
Just because something has been done and has not failed, doesnt mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline MountainDon

  • Administrator
  • Journeyman
  • *****
  • Posts: 15,793
  • Gender: Male
  • Jemez Mountains, NM; that's pronounced HEY-mess
    • My 15.75 x 30 Jemez Cabin
Re: insulation behind wood stove
« Reply #9 on: January 22, 2008, 04:26:45 PM »
I do believe in the efficacy of the air spaced wall shield..

http://countryplans.com/smf/index.php?topic=2335.msg36511#msg36511
Scroll down to the picture of the dial thermometer. Maybe you've seen it before, maybe not.

Just because something has been done and has not failed, doesnt mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline cholland

  • Junior Member
  • **
  • Posts: 77
  • Gender: Male
Re: insulation behind wood stove
« Reply #10 on: January 22, 2008, 09:39:04 PM »
I once installed a wood stove in a travel trailer.  Since I was going to be sleeping in there I wanted to be sure I wouldn't burn up.
Quality stoves will have a manufacturing plate with the minimum spacing needed.
For the one inch spacing I used 1/4" steel tube cut to one inch length.  I used long sheetrock screws and hung rockcrete board with one inch space at top and bottom.  Looks were not important to me so I left the rockcrete bare.
For the first month or so I would occasionally check the temp behind the board.  It was never much warmer than the rest of the room.  The wood paneling was hardly warm.  That one inch air space allows plenty of movement to prevent a fire from radiant heat.

Offline CWhite

  • Full Member
  • ***
  • Posts: 160
  • CountryPlans member
    • The Funky Chicken Art Project
Re: insulation behind wood stove
« Reply #11 on: January 23, 2008, 04:29:42 AM »
The stove I'm going to install is one I bought off of craigslist.com.  I have heated with wood for over 30 years, and for most of that time, without using back up systems. 

It is a fisher, brick lined, and air tight.  It is so heavy we can't move it into the house without a real plan.  I bought it from an older couple who moved up from Florida about 23 years ago, installed it in their basement after advice from folks afraid of our 'severe' weather .....they lived a bit south of Atlanta, GA.....and then only used the stove once for about 20 minutes before they put it out.  The woman told me she was afraid of it. 

Anyway, it's like brand new!  It was kept dry, and dusted for 23 years.  I got it for $250.00.    There are no specs written on it anywhere, about distances, probably due to its age, but I'll search the Fisher site to see what they recommend for this size stove currently.  The sub-contractor who installed the triple wall pipe through the floor and roof gave me an idea of how far, and set the pipes that distance. 

I like the idea of using screws through pipes cut to  1" behind rockcrete board.  That will work.   Then, I'll stack the rock on it.  There is room, because the pipe comes out of the back of the stove. 

Thanks again.
Christina

Offline MountainDon

  • Administrator
  • Journeyman
  • *****
  • Posts: 15,793
  • Gender: Male
  • Jemez Mountains, NM; that's pronounced HEY-mess
    • My 15.75 x 30 Jemez Cabin
Re: insulation behind wood stove
« Reply #12 on: January 23, 2008, 06:53:00 AM »
If that stove has no UL label it's possible you might have a problem with your home owner insurance.   :-\
Just because something has been done and has not failed, doesnt mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline glenn kangiser

  • The Troglodyte
  • Administrator
  • Journeyman
  • *****
  • Posts: 24,686
  • Gender: Male
  • Central California Sierras- Home of Yosemite NP
    • Underground Cabin
Re: insulation behind wood stove
« Reply #13 on: January 23, 2008, 07:26:30 AM »
Seems there was an allowance for unlisted stoves - no label - but distances increased.  Sounds like a Fisher from the early years if no tag.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

Offline NM_Shooter

  • Journeyman
  • *****
  • Posts: 2,759
  • Gender: Male
  • Sometimes I sit and think. Mostly I just sit.
Re: insulation behind wood stove
« Reply #14 on: January 23, 2008, 03:10:14 PM »
I was right at the limit for clearance.  If I measure to the rock face it does not meet clearance, but it does to the wood studs behind.  I still wanted a sheild, but did not want to mount it permanently to the wall.  I made a hinged frame out of angle iron, and bought some scrap polished stainless to put in the frames.  It provides some "shade" for the wall behind, but does not completely obscure the stonework.  Here is a picture, assuming I can get photobucket to work right...

-f-

"Officium Vacuus Auctorita"

Offline tc-vt

  • Full Member
  • ***
  • Posts: 160
  • Gender: Male
Re: insulation behind wood stove
« Reply #15 on: January 23, 2008, 03:26:37 PM »
Re: what Glenn said...

Over time the character of the wood can be changed by extended exposure to heat.

Temperature        Time (days)        Condition
107C   224F           1050                light chocolate color
120C   248F           1235                brittle, dark-chocolate color
140C   284F           320                  lost 45% of weight, became like charcoal
150C   302F           165                  lost 65% of weight, became like charcoal

...and I believe the flash point gets lower and lower as the wood carbonizes.  This reminds me of something I ard or read about a woodstove showroom (it might have been VT Castings) that was undergoing renovation.  When one of the stoves was moved they were surprised to see the wood floor beneath it had turned black. 

Tom

Offline MountainDon

  • Administrator
  • Journeyman
  • *****
  • Posts: 15,793
  • Gender: Male
  • Jemez Mountains, NM; that's pronounced HEY-mess
    • My 15.75 x 30 Jemez Cabin
Re: insulation behind wood stove
« Reply #16 on: January 23, 2008, 03:40:13 PM »
...and I believe the flash point gets lower and lower as the wood carbonizes. 
Correct. Normal wood will ignite somewhere between 450 - 500 degrees F, whereas carbonized wood my ignite as low as 250 F or thereabouts.

Many years ago when steam heating was first being retrofitted there were some cases of fires in walls where a vertical steam pipe had been installed close to vertical studs or boards. It took a few years, but they blamed the fires on the extended elevated heat levels caused by the steam pipes.

Info for non-rated or uncertified wood stoves and clearances...
http://www.woodheat.org/safety/safeinstallation.htm
http://hearth.com/econtent/index.php/articles/wood_stove_clearances_installing_it_safely
http://www.hearth.com/content/images/uploads/nfpachart1.jpg

Unfortunately there seems to be some conflicting info. In the first link it states that an unlisted solid fuel appliance must have 48" to a combustible surface and in the second link it states 36".  ??? These are for non-protected surfaces. The chart uses the 36" as base point.   :-\

Hope this helps more than it muddles.
Just because something has been done and has not failed, doesnt mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline glenn kangiser

  • The Troglodyte
  • Administrator
  • Journeyman
  • *****
  • Posts: 24,686
  • Gender: Male
  • Central California Sierras- Home of Yosemite NP
    • Underground Cabin
Re: insulation behind wood stove
« Reply #17 on: January 23, 2008, 04:08:50 PM »
I always heard the 36" and thought that was ridiculous, but that sounds right to me.
"Always work from the general to the specific." J. Raabe

Glenn's Underground Cabin  http://countryplans.com/smf/index.php?topic=151.0

Please put your area in your sig line so we can assist with location specific answers.

Offline MountainDon

  • Administrator
  • Journeyman
  • *****
  • Posts: 15,793
  • Gender: Male
  • Jemez Mountains, NM; that's pronounced HEY-mess
    • My 15.75 x 30 Jemez Cabin
Re: insulation behind wood stove
« Reply #18 on: January 23, 2008, 04:16:53 PM »
There's also a difference between Canadian and American requirements.  d*  IIRC, the Canadian standards call for greater clearances.  ???
Just because something has been done and has not failed, doesnt mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?