hot air wood furnance

[Wallys World]

Maybe I'm nuts but I going to try! I have a hot air add on wood furnance that we used in New York state to heat our house. The house we are in now in Virginia has a set of nasty outside stairs to get to the basement and my wife will not go down them to fill a wood furnance, not to mention getting the wood down there. I thought (now there is a dangerous thing) :D, why can't I put the furnance outside? I've seen ads for a couple of this type, why not try. So i cranked up the WM LT15 and here is what I have so far.


Front view



Rear view



Side view
I am going to run insulated flex duct from the furnance and tie into the exhisting heat run and cold air retun in the house. They will be boxed in a foam "duct" I'll make from the pink foam insulation. We don't have the extreme low temperatures around here, last year it only got to 25 degrees.

[beenthere]

Now there is a project. 
I'm wondering how much heat the small room area can stand before it also becomes combustible. That would be my main concern.

Will you insulate the building or leave it uninsulated? Maybe line it with drywall to protect the wood studs and siding/roof from the heat?

The fact it is away from the house, having the building ignite might not be a major concern.

Hope it works out for you. 

[Wallys World]

The furnance is surrounded by the air jacket, it doesn't get hot enough to burn you, so i really don't know how much heat is really lost by it. I don't know if I will insulate the house, don't know if you will really gain much heat by doing it. I guess it will be by trail and error.

[ely]

i am going to do about the same thing for heat in our shop. if that works i will do it in my house too.

[Mr Mom]

I would inclose it and insulate it. Being that the unit is not insulated itself.
I am thinking about doing somthing like that next year.

Thanks Alot Mr Mom

[Wallys World]

Once i finish milling the siding and get the front door installed maybe I will insulate it. Couldn't hurt it to do. It will be at least until next week until I get back to working on it, I'm on my working 7 days straight right now.

[woodmills1]

from the picture it looks like at least the front and maybe the back of your stove are not covered by the air chamber.  I would think that the heat from front and back could set you up for a very combustable situation.

[Wallys World]

I was planning to use concrete board (the stuff you put under tile floors) on the back wall, and I could line the front door with it also. That should help the "fire" factor.

[woodmills1]

please remember that you cannot mount fireproof material directly in contact with combustables.  I have seen the results of such installations.  In one, the homeowner had applied aluminum foil directly to a wall that was about 2 feet from the side of his stove.  I noticed this when I delivered some firewood.  I pointed it out but he was a nonbeliever.  I asked him to pull the foil down and that I would put it back if all was well.  The wall behind was all charred black..........he was livid and very thankful.

proper installation requires an air space between the wall and the fireproof material, as well as air space at top, bottem and sides.  I make little spacers from electrical conduit to hold the material out from the wall.

[Kelvin]

Howdy,
Just thought i'd mention my little incident with my experiment in using a hot air furnace setup just like you are doing on my solar kilns.  I burned them up somehow.  I even seperated the building by 20' or so with what i thought to be non combustable fiberglass insulated ducts, but it jumped it.  It obviously was quite a bit different in that the internal temps were in the 160-180 range so combustion was much easier.  I'm now adding one onto my house but i'm building a mudroom addition and adding a little section onto that where i can install the furnace.  I'm doing a couple of things.  Having access to all sides of the furnace to inspect and keep clear.  using non combustible materials for wall coverings, floor and ceiling.  (i also used cement board in my previous one, but it was a lot smaller and so tighter to the walls then yours)  Having fire alarms, and so i don't think it should be anymore exposure to fire than my other woodstove.  THe advantage to keeping in the house is keeping the heat from the chimney and stove itself in the house as opposed to outdoors.  This is a big factor in why outdoor wood boilers consume about 2x's the firewood as inside burners.  You are loosing alot of heat off the units.  Maybe its warmer in your area as well.  I think it can be done just fine, but its good to make precautions like the post above about seperating the non-combustables from combustables with stand offs.  Good luck and have fun.
Kelvin

[sawmilllawyer]

Kelvin, I remember that! Why not build the building out of metal studs and cover with sheet metal?  Lot lower fire hazard, i would think.

[Wallys World]

I like the idea of the spacers behind the concrete or sheet rock. Never thought about that. I'll try it behind the concrete board. I think I'll use 2 or 3 washers.

[thecfarm]

When I was working for the state,insulating low incomes homes,if we needed spacers behind fire code board we used ½ copper unions.Seems like the state required 1" space of non combustible space behind it.

[woodmills1]

Yes I think 1" is what is needed behind the board as well as at top and bottem.  The idea is to get a convection current to carry away the heat.

[beenthere]

Here is a source document for information extracted from the fire code, that can help for guidance.

http://www.cdc.gov/nasd/docs/d001001-d001100/d001052/d001052.html

Being Wally's furnace is away from the house, he won't be needing the margin of safety like it being in the home.

As wood heats up to the higher temps (of over 150° F), it becomes very dry and the ignition point is lower, and as well it loses strength. But, discoloration of the wood will be good indicators if this is happening, before any ignition occurs. (my take on it.. )

[woodmills1]

being away from the house means when the shed burns it may not take the house with it.