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tcmatt
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# Posted: 16 May 2013 10:26pm
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Does anyone have any ideas on alternatives to the fairly expensive ceramic spacers for a wood stove heat shield?
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ICC
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# Posted: 16 May 2013 11:50pm
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the NFPA rule simply states the spacers must be non combustible. i have used sections of brass, steel or copper tube. this is partly going to depend on what your inspector will permit. ask him/her. if there is no inspection use metal tubing or go for the gold and use ceramic. at a little over a dollar apiece they are not cheap but should not be a budget buster either.
the NFPA rule also states there can be no fasteners directly behind the stove.
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oldgringo
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# Posted: 17 May 2013 05:21am
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I built one out of Hardie board. Three pieces, hinged, free-standing.
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Steve961
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# Posted: 17 May 2013 03:12pm - Edited by: Steve961
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I used 1 1/2" steel studs run vertically behind 1/2" cement board. The steel studs were only 1" deep when rotated 90 degrees.
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tcmatt
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# Posted: 17 May 2013 03:17pm
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Steve,
Where did you get the steel studs and how much were they?
Thanks
Matt
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Steve961
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# Posted: 17 May 2013 04:27pm
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Matt:
I got them from Menards and they're only $2.73 for a 10' length. They do have 8' ones, but if your heat shield is going to be 5' or so, the 10' ones are a better value.
ProSTUD 1-5/8 x 10
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tcmatt
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# Posted: 17 May 2013 09:28pm
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Thanks Steve. Great idea. I've got an old jotul 602 that I'll be installing
, too.
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bldginsp
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# Posted: 18 May 2013 09:54am - Edited by: bldginsp
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I'm a bit mystified by this spacer thing. Obviously you dont' want to use a combustible material for the spacer, but what about heat transfer through the metal fastener? I guess the reason you are not supposed to put spacers/fasteners right behind the stove is so that the screw or nail that attaches to the combustible wall behind wont get overheated to the point that it will burn the stud it is driven into. So I've looked for, but haven't found, a non-metallic fastener, such as a ceramic. They do wondrous things with ceramics now, making router bits out of them etc. But even if they did make a useable ceramic screw it would be pricey I'm sure.
I plan to to build a brick surround for my woodstove which will allow a reduction of clearance to combustibles of 2/3. The brick has to be spaced 1" out from the wall. Standard masonry wall ties are made of corrugated metal. I'm doing a corner installation with the stove at 45 degrees, so there really isn't anyplace on the brick surround that is not 'behind' the stove. I'll just locate them as far away from the stove as possible.
Still, if the brick heats up, the ties heat up, and transfer heat to the wall behind. Maybe I just worry too much.
An alternative to the ceramic ties, along with metal pipe as ICC suggested, would be knobs from knob and tube wiring, if somehow you have access to a bunch of those.
Another alternative would be the ceramic spacers used in ceramic kilns to keep shelves apart during firing. They make them in all sizes. Pricey new, but a potter might have a bunch of old ones to give away. they are called 'bones' cause they look like vertabrae.
Now there's an idea- space your cement board out with old deer vertabrae.....
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Truecabin
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# Posted: 18 May 2013 10:49am - Edited by: Truecabin
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Quoting: bldginsp but what about heat transfer through the metal fastener?
yes there is heat transfer thru metal fastener but its only a tiny amount of heat on the cross section also the fastener is radiating more heat away along its length than whats conducting thru to the end. chasing down ceramic spacers for a one inch spacing is a waste of time , ceramic conducts heat too. unless your spacers are very thin like 1/8 or 1/4 inch then its important but if your spacer is like an inch then metal spacers and fasteners are fine. And use an inch, dont use 1/8 or 1/4 thats too close you wont get enough convective airflow behind. don't worry about the fastening which is 0.1% , just get the heat shield on there and put the other 99.9% of combustibles in the shade.
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Truecabin
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# Posted: 18 May 2013 10:55am
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vertebrae would work but might crumble over time. you can use glass or ceramic drawer pull knobs too but its a waste of time especially when you are doing this all behind a brick heat barrier. Make a temporary stack of bricks behind your stove and make a hot fire and feel the backside of the bricks your finger will be the warmer than the brick and if you can light anything on fire with your finger you have a bright future in the circus. you can use one inch slices of metal pipe or electrical conduit for spacers.
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Steve961
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# Posted: 18 May 2013 11:35am
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The nice thing about using steel stud spacers is that the fasteners used to attach the spacers to the wall are different from those that attach the cement board to the studs. Any screws that go into the wood studs in the wall have a layer of cement board between then and the heat source. The screws used to attach the cement board to the steel stud spacers are purposefully short so they don't go into the wall, only the spacers.
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tcmatt
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# Posted: 18 May 2013 03:44pm
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Steve,
I just picked up the metal studs from Menards. I was just going to lay the open side against the wall and screw into the wall studs using some leftover deck screws and use the same screws to screw my steel "firewall".
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OwenChristensen
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# Posted: 19 May 2013 06:35am
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Be sure to lift the cement board off the floor a little. That way as the airspace gets warm it draws cooler air in and the hot air exits the top. I put no spacers in the middle, only on the edge farther away from the stove. I tried hard to burn down one of my saunas last year. All the shampoo bottles melted and my solar light. It must have got over 200 deg. No wood scorching at all behind the stove.
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bldginsp
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# Posted: 19 May 2013 08:54am
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think I read somewhere that wood exposed to direct radiant heat of a woodstove will, over time, get a much lower combustion point, so that eventually it can burn at 200-250 degrees. So I'm going to put my moldings, which are outside of the brick surround, well out of range.
Thanks Truecabin- you are right that ceramic is a conductor as well. So they say, a typical masonry fireplace can get hot enough to ignite the wood around it if you keep a raging fire in it for, say, 24 hours or so, because the masonry absorbs and gradually conducts the heat.
It takes a 6 or 8 foot thick stone wall to acheive the same R value as a 2x4 wall, because stone is a conductor
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Truecabin
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# Posted: 19 May 2013 10:22am - Edited by: Truecabin
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Quoting: bldginsp radiant heat of a woodstove will, over time, get a much lower combustion point, so that eventually it can burn at 200-250 degrees.
i dont know about that, maybe if you put a match to very dry wood while its 250 deg it would burn easier a more dangerous condition but not ignite from the heat only Put a small block of same wood in your electric oven at 250 deg overnite and have a look in the morning then you will know more about that number
if you have brick behind the stove there is only the radiant heat from the backside of the brick not the stove and you can test that with a hot fire for a few housrs
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ICC
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# Posted: 20 May 2013 05:37pm
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Quoting: bldginsp think I read somewhere that wood exposed to direct radiant heat of a woodstove will, over time, get a much lower combustion point, so that eventually it can burn at 200-250 degrees. So I'm going to put my moldings, which are outside of the brick surround, well out of range.
Not sure of the exact temperature but YES if wood is exposed to high heat long enough the characteristic of the wood changes. It can then be ignited at much lower than expected temperatures. It may take a few years. There are recorded instances of fires breaking out in buildings with steam heating pipes that were either installed poorly or the wall later renovated without thought to the potential danger.
I have done remodeling on walls that had been in service with metal spacers for a couple of decades. Never seen any trace of pyrolization around the metal screws. As was mentioned the heat is likely dissipated before getting to the wood. As long as the screws are offset from being directly behind the stove though.
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bldginsp
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# Posted: 20 May 2013 06:06pm
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It's the 'directly behind' that I'm unsure of. In my case I'm putting a small stove at 45o to the corner, and the reduction in clearances afforded by the brick surround allows me to push the stove in at about 4 inches from the brick. In this case, the only place on the brick that is not 'directly behind' the stove is the outer sides of the brick. With this reasoning I can't put any masonry ties in the corner where the two brick walls meet, since that is directly behind. I'm going to put them there anyway, with air slots at the bottom so that air can circulate up behind the brick to cool it down. No ties in the brick closest to the stove, obviously.
It makes sense that heat would dissipate in a screw or nail holding a metal or other spacer. So should a metal masonry tie, which is surrounded by air and can easily cool.
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ICC
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# Posted: 20 May 2013 06:15pm
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great amount of surface area to the actual mass of the tie / screws / nails.. i think yours should work fine. the air space at the bottom is required according to the info I have read. open space at top as well to permit freely moving air.
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TheWildMan
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# Posted: 21 May 2013 12:54pm
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I used sections of copper pipe, pipe was found in a junk pile, used a hacksaw to cut into 2" sections. used a section of old roofing metal for shield (same junk pile), punched holes in the shield and passed long screws through, put the screw through the sections of pipe then screwed 2" into the wall studs behind.
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RandallD
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# Posted: 2 Sep 2015 07:01pm
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Steve916, is that a sock/glove drying rack hanging above the stove?
I love that idea.
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Steve961
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# Posted: 2 Sep 2015 08:37pm
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Quoting: RandallD Steve916, is that a sock/glove drying rack hanging above the stove? I love that idea.
Yep, that's exactly what it is. I got the idea from a friends cabin up in the Boundary Waters where he had a much larger one custom built around his wood stove chimney. Mine is just a very inexpensive Ikea hanging pot rack, but it works just fine. Unfortunately they don't sell them anymore.
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FishHog
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# Posted: 3 Sep 2015 08:36am
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Quoting: Steve961 Yep, that's exactly what it is. I got the idea from a friends cabin up in the Boundary Waters where he had a much larger one custom built around his wood stove chimney. Mine is just a very inexpensive Ikea hanging pot rack, but it works just fine. Unfortunately they don't sell them anymore.
Great idea. I might have to copy that. I just finished building my boot dryer rack. I'll try to remember to take a pic and post it after I mount it in the cabin.
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Woodeye
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# Posted: 4 Sep 2015 09:47am
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I have stainless steel sheet metal with a 1/2 in. hem to protect from sharp edges and then held off of the wood wall using ceramic electric fence insulators. The stainless may not appeal to some but I'm a cheese maker so stainless is my second favorite color, it reflects heat and with the air gap the wall always stays cool. I had cement board that did not work, heat radiated through it and I was sure I would eventually have a fire.
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Northstar6
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# Posted: 4 Sep 2015 10:09am
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I put boiler-insulation on the inside of the stove covering the sides next to combustable material - a very cheap easy fix.
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R9R Photography
Member
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# Posted: 29 Sep 2015 08:18pm
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1/2" cement board, spaced by old pallet racking parts. Stainless lag bolts through to the wall. 1" air gap at the bottom. Just installed this past weekend, touch ups to come next visit to the cabin.
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Julie2Oregon
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# Posted: 30 Sep 2015 12:21am
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This is probably a super-stupid question but WTH. I'm blonde. Is there a reason that you have to put the stove near a wall? I'm not planning to do that. Should I be?
Here's the thing. My loft is going to be above my kitchen and bathroom so it will be like the ceiling for those two rooms, not quite half of the cabin, lengthwise. I want to put the woodstove between the kitchen and the rest of the living space so that the fire is facing the living room and the stove side for kettles/pots is facing the kitchen.
That placement will also send the stove pipe straight up solely through the cathedral ceiling, not the loft, and emerge out near peak pitch of the roof, which means needing less of the mega-expensive outside pipe and creating a good draw.
Anyhoo, the stove will be about 6 feet away from its closest walls. Is this a problem for heat distribution throughout the cabin?
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MtnDon
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# Posted: 30 Sep 2015 01:36am - Edited by: MtnDon
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Our previous house was similar. We could walk around all 4 sides. Central location made for good distribution of heat. The only complication was ducting the fresh air inlet through the floor instead of anexterior wall.
Regarding the cathedral ceiling and using long lengths of black stove pipe.... some stoves have maximum listed lengths for black pipe from stove up. Too long a length can cause too much cooling of the flue. I know someone who had draft issues with a very high 2 story ceiling run. Only in early fall , late spring when fires were smaller. Our VC Aspen has a max listed length of 8 feet IIRC. Have to check that. In essence I'm saying that a tall cathedral ceiling might require some insulated pipe drop from where the ceiling thimble is ,down a ways. Not savingas much as one might hope for.
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Julie2Oregon
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# Posted: 30 Sep 2015 02:53am
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Ah, OK. Thanks much, MtnDon! I will check that, for sure, and adjust accordingly. I'm very glad to know that heat distribution won't be a problem, though!
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KinAlberta
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# Posted: 25 Oct 2015 03:11pm - Edited by: KinAlberta
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Could one use high heat silicone and 1" square ceramic tiles as spacers?
While I'm at it... Anyone use ceramic or porcelain tiles on the visible face of cement board or over an extruded mesh / metal face?
I was going to do that and just use spots of mortar or high heat silicone in order to leave an air circulation space behind every tile, thinking that otherwise the tiles would just heat up and transmit the heat through the board and closer to the wall.
Some background: I have old unrated wood cook stove that needs to sit close to a pine board wall, so I was going to build a multiple layered tin and cement board heat shield and face it with tile (or maybe just tile the left and right sides and put a metal strip up the centre closest to the pipe.
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KinAlberta
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# Posted: 17 Jan 2017 03:26pm
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Saw a partial box of these BBQ briquettes yesterday in a Habitat for Humanity store. They could be used as spacers between layers on a heat shield.
Grill Greats Ceramic Grill Tiles
Item #196-315
Modern alternative for briquets and lava-rock with superior heat distribution. Perforated ceramic tiles reduce flare-ups, and help give great barbeque flavor. 2" X 3-1/2" tiles, 45 per carton cover 315 square inches or 13" X 24" surface area.
Our Price: $24.95
In Stock: grill parts online
http://www.grillparts.com/broilmaster/?product_id=196-315
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