Hello all, hope everyone had a safe new years 8).
I'm looking into getting a new indoor furnace. In fact like the title says, I wouldn't mind building one myself. This way it would be to my specs and it would just be a good project.
The idea is to base it off the HotBlast type forced air furnaces, but with deminsions to my spec.
If I go through with it, I'll have plenty of questions so thanks in advance for any help.
I'd like the fire box to be:
Height- 28"-30"
Width - 18-20"
Depth- 30-32"+
I would probably use the doors from an old retired Ashley circulator type stove.
First, would 3/16" plate be plenty for the fire box?
And for the flue, would it be best to pipe it directly out or would it be good to make a secondary chamber or some sort?
I sure have no idea. But on my Heatmor the smoke goes up at the front of the firebox into a 4X8 inch chamber that goes the full lenght of the firewood and than out. I also have a water cool feed door. Good luck.
i have built a couple. i used 1/4" plate. first one had a smoke shelf in it. the other i used well casing. ran it almost to the door. and put the air intake in the door worked pretty good. also welded 1/4x2 flat bar on the outside on edge to help it heat and keep the firebox straight
You should check with your insurance company first. A home built furnace no matter how well built may not satisfy them. A UL tag or similar certification may be required.
That's a very good point about the insurance companies. I dont think the companies around here even like indoor wood stoves period. I'm not too worried about that part though. If something were to come up I could always convert it to an outdoor unit or something.
Quote from: snowstorm on January 01, 2015, 06:28:07 PM
i have built a couple. i used 1/4" plate. first one had a smoke shelf in it. the other i used well casing. ran it almost to the door. and put the air intake in the door worked pretty good. also welded 1/4x2 flat bar on the outside on edge to help it heat and keep the firebox straight
Since 3/16" plate would be a little cheaper and lighter, would it do the trick for the box?
Also I was thinking about welding some steel angle along the box to work as "fins" and to strengthen the box.
The insurance company's are the same around here. They won't insure houses or even out building with home made wood burning devices in them any more. They don't even like legal wood burning devices in houses and charge extra. When we were looking at adding a indoor wood furnance in our house 10 years ago the insurance company said the same as no way. so we did a Garn instead out in a out building and I heat my shop and house with it.
Woodcutter, the fire box should be fire bricked at least to over where the fire is, the reflected heat will help getting less smoke and a more efficient burn. Frank C.
OK, I was wondering if fire brick would be a good idea. Thanks for clearing that up.
Looks like 9x4.5x1.25" fire brick can be bought for under $3 each so lookin at $50+/- just for that if I do a 9" high row around the inside of the box.
I still have to price some steel plate for the box, some heavy 6" steel pipe and some other misc.
If I was going to build my own hot air wood burner I surely wouldn't model after a Hotblast. I would use a round fire box, eliminating the need for external re enforcement's. I would also use a round smoke chamber above the firebox to take advantage of all the heat possible. I would also give it a secondary air intake to burn of some of the smoke.
How big of an area are you wanting to heat? My firebox is 38.5" deep and about 18" diameter and the smoke chamber is a little smaller. The jacket is lined with fiberglass insulation and a baffle so the air blows from under up and around but can't get back to the starting point. I use a regular furnace fan and have 10" in and out ducts. My burner is outside my house, love it that way!
dave
The house is around 1100sqft I believe. I don't really mean it will be just like the hotblast, just using the basic concept with improvements. ;D
For the smoke chamber, I was thinking of using some 6" heavy steel pipe the length of the fire box with 2 inlets. Sound like that would work?
Oh, and for the draft I plan to use 1 or 2 thermo adjustable flaps. I want it to burn clean but I'm going to make it to where I can slow it down to control an over fireing condition if it happens.
I might draw up a picture of what I had in mind.
I'd be interested in seeing what you plan to build.
OK I'll try to get a pic drawn up on what I'd like to make.
Woodcutter, insted of expensive firebrick I just used cement brick from Home Depot not mortered but just laid in. They will last a long time and its no trick to replace if one does crack. Frank C.
Not familiar with the design you are talking about, is that a gassification type of furnace? I have been doing some research into building a gassifier boiler that I plan to set outside. I loved the one we had at our last place but don't want to sink that kind of $$ into another one.
Southside logger, I'm not sure what the furnace I want to build is called, but its not a boiler type. The hot air from the furnace is pushed through the ducts.
bandmiller2, thanks for the tip. I'll give that some consideration 8)
Quote from: bandmiller2 on January 05, 2015, 08:41:37 PM
Woodcutter, insted of expensive firebrick I just used cement brick from Home Depot not mortered but just laid in. They will last a long time and its no trick to replace if one does crack. Frank C.
The difference between regular cement brick and fire brick is that fire brick insulates. It will not transmit heat through to the other side nearly as much as cement. Also, as stated, it cement will crack, sometimes with energy! I found fire brick for about 2 bucks each at a rock and stone store. I used them to make a (gas) welding table. They are fairly heavy, probably 2/3 the weight of clay brick. There are also some fire brick that is extremely light weight, but very brittle, like Styrofoam. The prices varied GREATLY, so shop around.
Come to think of it I have seen concrete block explode, moisture or air pockets inside I guess :o
John, you speakth the truth but I have used boath fire brick and cement brick the heat transfer is not a bad thing. If the furnace is heated up slowly theirs no problem with the brick as any moisture within is driven off slowly. If you can find cheap or used fire brick use them they are the premium product. Just saying cement brick can be used. Frank C.
This may be a little off topic, but you mentioned the possibility of having an outdoor wood furnace. I went round and round with my insurance company when I wanted to install a wood furnace in my shop. Not at all the same for an indoor wood furnace for in a house as I found out. The insurance company was concerned with any heating appliance with an open flame that was closer than three feet off the floor. Flamable vapors from gasoline, paint thinners, etc. The only way they would allow an indoor wood furnace, was if I built a separate room to enclose the furnace. This was not feasible in my situation. They would not even consider any type of heater that did not have an appropriate testing agency stamp on it. After making sure it was acceptable to my insurance company, I installed a propane ceiling hung heater. I hated it. Last year we had one of the coldest winters I've seen, and the cost of propane went thru the roof. I used it very little because of the cost to run it. Moving ahead to this past October. I found an outdoor wood furnace that looked like it would be what I really wanted. After another talk with my insurance company, and sending them all the info they required, they approved the installation. I have been warm and toasty every day I have worked in the shop since. I put a load in a couple times a day, and now let the propane heater keep my shop at 45 degrees overnight.
I guess the reason for this post is to make sure you check with your insurance company. Every situation is different, and needs to be approved by them for you to have coverage. At least that is what I found.
Here is a picture of what I installed.
(https://forestryforum.com/gallery/albums/userpics/10927/image~39.jpg)
the fire brick on the sides of my firebox are on a slight angle so they do not have a tendency to fall over. the firebrick on the front and back are straight up and down. no problem with the ones in back moving but the ones in front move some if they get hit while loading wood. the piece (angle iron) that held them uprite broke off a few years ago. i'm going to fix that soon. my furnace firebox is made of 1/8 inch. that's what i had at the time. that was 25 years ago. i would go 3/16 or 1/4 if thats what i had. 3/16 if i had to buy the steel. a friend had one built of 1/2 inch and it was a failure according to him. most of the heat went up the chimney instead of through the heavy walls. my furnace is a downdraft design like the old tempwoods.
For a furnace to be low smoke and efficient you must have a hot concentrated fire, that cannot be maintained with fire agenst a steel jacket with water on the other side. Masonry to maintain and reflect heat back into the fire then above that your steel (or cast iron) water jacket. Years ago when steam powered our country dutch ovens were used especially with damp low grade fuel. A dutch oven is simply a masonry furnace with the exiting hot gasses passing through a boiler. Frank C.
OK so sounds like 3/16" plate steel would work fine then 8)
I planned for the fire bricks to stand pretty much straight up and down. I the plan is to make an angle iron retainer that I can just slide the bricks in from one end.
Going to call and get a ballpark price on 3/16 plate today.
Next thing is I need to figure out what to use for grates on the bottom. I want it to have grates and a decent size ashpan.
I wouldn't bother with grates. IMO they are just in the way, take up room, warp from the heat, etc.
Keep a good bed of ash in the bottom for the fire, use an ash shovel to sort out charcoal and live coals when removing some of the ash as it builds up. Amount of ash will depend on the wood species being burned. Some more, some way less.
QuoteFor a furnace to be low smoke and efficient you must have a hot concentrated fire, that cannot be maintained with fire agenst a steel jacket with water on the other side.
I have a water jacket around the 3/16" steel chamber that I burn wood in for heat. Have no major smoke problem and figure my boiler is as efficient as they come (may be some short of a gasser's efficiency but with many fewer problems).
There is a layer of creosote that maintains itself on the fire side of the steel water jacket but don't see any negative effect of that layer. Doesn't get more than about 1/4" thick, never scrape it off, and never have had the steel rust through (going on 35 years now).
I don't know, I've always liked stoves with grates.
Looks like about $3.83/ sqft for 3/16" plate steel locally.
Quote from: Woodcutter_Mo on January 07, 2015, 11:45:28 AM
I don't know, I've always liked stoves with grates. And I burn mostly oak and some hickory, occasionally some ash or walnut ect if I just happen to cut some.
Looks like about $3.83/ sqft for 3/16" plate steel locally.
Sorry, somehow quoted my own post on accident instead of modify.
Skip the grates. More bother then they're worth. Also, the very bottom of your firebox should have the firebricks angled in on a V shape, not square. The V shape will concentrate the coals and give you a much cleaner burn.
Personally, I like the rocket stoves built with 55 gallon drum for a radiator (bell). They burn very hot, very clean and with minimum wood. There are some great ideas using batch burners for the firebox.
This is the last of a 5 part series of a rocket stove built by a fellow in NZ I believe. Instead of a barrel for the bell, he fabbed a square one. It's one of the best designs I've seen. Very clever.
http://m.youtube.com/watch?v=ZJ5XbLyrVlY
I vote for grates too. I have them in my OWB for 7 years and the fire has only been out a month in all those years. They are holding up quite well. I only have grates down the middle,the edges are filled with sand.
Yea I really like grates. Pretty sure I'll install some. I'd even like shaker grates preferably but fixed grates would do the trick.
Thanks for the tip about the firebricks being set in a "V" instead of strait up and down. That makes sense.
In case you have any remote interest in outdoor hydronic, I'll describe what I did a couple years ago. 250 gal propane tank inside 500 gal propane tank, end of the 250 is the door for the wood. That is boiler plate I'm pretty sure. It's 100 ft from the house, circulates all the time, heats hot water real good with a water to water exchanger the size of a textbook. Cons: it does smoke and wastes some wood. Pros: hot water, it's 73 in the house when we get home, and the place will not be on fire, no dust mice bugs smoke in or near house. Have $2000 in parts, for install and exchangers and all. Missouri. Hot water must be a significant energy savings, use alot of wood on the weekends, washing clothes I guess. No grates, scoop it in the loader bucket every couple months.
Cutter, your furnace if you like grates use,em but you could make them easily removable and try it both ways. My furnace uses no grates I do believe you use less wood and can carry a fire longer with no grates. Frank C.
I had a old Riteway, The metal was starting to rust thu, as was only used in the summer time. So I took it apart, saving all the parts, including grates. Brought 1/8" steel, and cut it out the same size as the Riteway was. Welded it up and installed all the Riteway parts, put in new fire brick, and grates. put the doors on just like the Riteway, and heat control. Use it in the shop, and shake down the ashes, use the ash Pan. Works good, but to make more heat, keep a small fire over night. Insurance company wanted to be sure that it would be under control.
SquareG
Your boiler sounds very interesting. Sure would like to see some pics of your setup. It is an enlarged design for what I have as an indoor boiler unit. Works great.
Hope to hear more.
my furnace doesn't have grates and holds coals for 12 or more hours if we're gone and can not fire. also i have a stainless steel 'u' shaped tube inside the firebox that thermal siphons through my electric hot water heater so when there is a fire i have free extremely hot water. very simple installation if you can get the hotwater heater close enuf. jayg
Quote from: bandmiller2 on January 08, 2015, 08:36:29 AM
Cutter, your furnace if you like grates use,em but you could make them easily removable and try it both ways. My furnace uses no grates I do believe you use less wood and can carry a fire longer with no grates. Frank C.
Yea I'll probably make the grates removable, I may try it without them just to test it. I just like being able to get a lot of the ash without waiting for the fire to die down ect, don't smoke the house as bad either :)