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  1. #1
    Join Date
    Aug 2004
    Location
    Milan Michigan
    Posts
    1,690

    Default Building a out door wood furnace for shop addition

    I built a 40 x 80 addition onto my existing 38' x 40' shop, the ceiling is 18' tall.
    I used to have a wood stove in the existing shop that worked really well but I sold it a week ago.

    I figured that I'm going to need a bigger wood furnace and I called the mechanical inspector to find out what the code is just to find out that they dont allow a wood stove in a shop where oxygen and acytelene are stored because you never know when a spark might cause the oxygen cylinder to blow up.
    I said ( Do you realize that I'm a welding shop and thats what we do make sparks all day long and alot of the time we do it with the oxygen and acytelene torch ) He said
    ( Ya I know, You can call the state inspector and find out what he says. It turned out to be the same response )

    Years ago I would have pushed the issue but because of insurance reasons its easier to do what they say. That and my new stove wont be UL Listed.

    I now have to heat 4,720 sq ft with a 18' ceiling.

    I bought a 550 cfm blower that kicked butt by itself but was useless when trying to push air out of two 8" ducts so I removed it and ordered a 1,400cfm blower.

    I have a 2-1/2" gap on the sides and a 3" gap on the top and bottom, The air has to run back and forth 5 times before it comes out of the 2 ducts 8" diameter.

    The inside fire box can take a 35" long log and is 27" wide x 26" tall now that I installed the fire brick

    I'm going to start on a fire proof building to put it in tomorrow and my plans are to pack insulation between the walls of the building and the stove, I will install a furnace duct with a filter on it for the cold air return, There will be approximately a 12" gap between the 2 buildings and I will have to insulate the two 8" duct pipe.

    All constructive criticism is welcome.

  2. #2
    Join Date
    Dec 2010
    Location
    kamloops bc canada
    Posts
    1

    Default

    By now you probably have your furnace finished.

    I was going to say, you need much more duct than two 8 inchers. Maybe fab a duct out of 45 gal drums, that would be the size you would need.

    How about some pics of your completed furnace?

  3. #3

    Default

    I'm an amateur for sure, but in the process of becoming a total pro ; )

    Can you house the oxy/acy in a seperate shed and pipe it in to be legal? Then you're golden.

    The most efficient home made wood burners seem to be designed to produce low temp wood gas in a lower chamber, then burn it at high temp with additional air input in a small upper chamber.

    Or, use a wood fire boiler and a heat exchanger (like a truck radiator) to put the btu's into the building but that get's slightly more complicated but more efficient I believe.

    I agree that you have too many cubic feet to heat using those small ducts. A 1000 sq ft house has ductwork that large.

    4700 sq ft with 18' ceiling requires a lot of heat in low outside temps. Is the building insulated? Lot's of heat and a large air mover is what comes to my mind.

    HVAC professionals with wood burning experience may have a lot better input than me : )

    My last tip is: Carhartt, they make groovey arctic gear. Two pairs of good wool socks with waterproof insulated boots. good expedition weight long handles, wool glove liners under welding gloves and over surgical gloves and silk liners, neck gaiter + US GI cold weather face shield, Carhartt stocking cap, two or three Carhartt long sleeve t-shirts (one a turtleneck), sweatshirt, hoodie, insulated bibs, arctic coat. There ya go, sleep comfortably in 40 below but dexterity will suffer a bit.
    Of course I only work outside, but that's my recipie for low,low temp/high, high wind.
    Or, better yet make your living in the temperate months and sit in the recliner and watch "Gunsmoke" reruns during the winter, drinking coffee/Kentucky Bourban with the Lovely Bride.
    Last edited by JTMcC; 12-10-2012 at 04:36 PM.
    Some days you eat the bear. And some days the bear eats you.

  4. #4
    Join Date
    Aug 2007
    Location
    St. Paul Park MN
    Posts
    132

    Default shop wood stove

    Quote Originally Posted by Portable Welder View Post
    I built a 40 x 80 addition onto my existing 38' x 40' shop, the ceiling is 18' tall.
    I used to have a wood stove in the existing shop that worked really well but I sold it a week ago.

    I figured that I'm going to need a bigger wood furnace and I called the mechanical inspector to find out what the code is just to find out that they dont allow a wood stove in a shop where oxygen and acytelene are stored because you never know when a spark might cause the oxygen cylinder to blow up.
    I said ( Do you realize that I'm a welding shop and thats what we do make sparks all day long and alot of the time we do it with the oxygen and acytelene torch ) He said
    ( Ya I know, You can call the state inspector and find out what he says. It turned out to be the same response )

    Years ago I would have pushed the issue but because of insurance reasons its easier to do what they say. That and my new stove wont be UL Listed.

    I now have to heat 4,720 sq ft with a 18' ceiling.

    I bought a 550 cfm blower that kicked butt by itself but was useless when trying to push air out of two 8" ducts so I removed it and ordered a 1,400cfm blower.

    I have a 2-1/2" gap on the sides and a 3" gap on the top and bottom, The air has to run back and forth 5 times before it comes out of the 2 ducts 8" diameter.

    The inside fire box can take a 35" long log and is 27" wide x 26" tall now that I installed the fire brick

    I'm going to start on a fire proof building to put it in tomorrow and my plans are to pack insulation between the walls of the building and the stove, I will install a furnace duct with a filter on it for the cold air return, There will be approximately a 12" gap between the 2 buildings and I will have to insulate the two 8" duct pipe.

    All constructive criticism is welcome.
    i pushed the fire marshall and insurance company over the wood stove in the shop. I have heated a 40' x 128' with 16 foot ceiling with a wood stove in the shop for 33 years now. Finally got them to understand which is more dangerous molen metal flying around the shop from torch or welding and what about the grinders throwing sparks every where? They finally decided a fire in a barrel made of 1/4" shell was less dangerous.

  5. #5
    Join Date
    Aug 2004
    Location
    Milan Michigan
    Posts
    1,690

    Default

    Sorry no pictures yet, I lost my digital camera.

    The building is done other than my cranes and finished electrical and completely liner paneled paneled on the inside, The walls have R-19 insulation and they came back the other day to blow the ceiling so I have R-38 up there. The temputure is about 30 degrees F. outside and the building is at 65 degrees.

    The forced air wood furnace is heating the new portion that is 40' x 80' with 18' ceiling and my original building that is 38' x 40' with a 16' ceiling and I have the furnace in the old section turned down to 55 degrees so its not comming on.

    As far as the duct work size having ( 2 ) 8" ducts blowing heat into the building with a 8" x 16" cold air return ( Yes this is what you would have to heat a 2000 sq ft house normally but the difference is that it comes on and off in a house while in the shop it stays on full time. )

    When I come in in the morning the thermometer reads about 56 to 58 degrees and by 3 hrs later its up to 62 to 65 F and the thermometer is on the other side of the shop from the stove.

    The new stove eats alot of wood probably a face chord a week.

    I'm also going to install a 150,000 BTU radiant tube heater for when it gets real cold and to maintain temputure at night or for when we are out on jobs for a week at a time to keep the shop heated to a min. of 50 degrees.
    Last edited by Portable Welder; 12-15-2012 at 08:01 AM.

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