Outdoor Wood Furnace Info
Outdoor Furnaces - Manufacturers with NON EPA-Certified Models Only => Home Made => Topic started by: Rscott on December 07, 2014, 04:27:14 PM
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Hi yall. My first question is, can a firebox be too big? I'm thinking not, but, then I got to thinking. Maybe as the wood burns down there might not be enough fire/heat to properly heat the large and almost empty firebox enough to produce usable heat.
If kept loaded I suppose this wouldn't be an issue though.
What I'm planning is a firebox apx 36" across x 48"high x 60 deep. My plan is to build it like a stretched out octagon. If that makes any sense.
I have 3/8" mild steel for the whole build. But considering using 1/2" on the very top and possibly the bottom. Doubt I'd need to but could.
This will be a forced air furnace with a stoker blower and hot air blower on thermostats.
Also wondering about stack placement. I'm thinking through the top but also considering out the back. Both would be apx 2/3rd to halfway into the firebox to hopefully pull more heat off the available fire.
We'll, any suggestions would be great before I screw up something simple.
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Read,Read,Read, there are several threads on here regarding home built units! Allow me to ask a few important questions you should be asking yourself. Why build it yourself? What is your budget? Do you have the knowledge, Time and funds to do it right?
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Read,Read,Read, there are several threads on here regarding home built units! Allow me to ask a few important questions you should be asking yourself. Why build it yourself? What is your budget? Do you have the knowledge, Time and funds to do it right?
Why pay someone to do what I can do?
Budget? What budget? We Don't need no stinking budget. (Though actually were good there) all steel is already here. I'll make decisions on blowers etc once the main unit is built.
Time is the one item I'm in short of. But that's why I'm starting now. Once built, I should have a year our so till we build the house it's being built for. Till then it'll be used on our shop. A test run if you will.
The design seems logical, lil things could make it less efficient. Hence my questions.
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OK, Good answers, I have some Ideas that may help, I'll PM you my contact info.
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Well I think I've made a design change already. I'm thinking that 48" wide and 36" high will be more efficient for transferring heat. And will accommodate skids. Slight change on the bottom of the firebox so as to fall wood onto the grate, but otherwise the same fire box laid on its side.
Still the same volume, maybe slightly more do to bottom being sloped, and more surface area being heated directly above the fire.
Any thoughts?
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48" wide makes for a lot of dead space unless you're planning on keeping it pretty full most of the time, it's pretty much agreed upon the best way to stretch your wood is to load for 12 hour burns.
Thinking of a big single door or a double? either one that size is A: going to be heavy, B: prone to warpage.
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I'd like a single door. But barn doors wouldn't hurt my feelings. But that's twice sealing. I'm picturing the door pinned and on brass bushings.
But then I could load it with the tractor.
But upright it can soak heat.
But then again being on demand forced air it'd get hot fast for short periods.
So maybe taller is better?
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I think with doors of either single or double being a forced air instead of water cooled warping will still be a problem.
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I think with doors of either single or double being a forced air instead of water cooled warping will still be a problem.
Ok let's take the door out of the equation for a minute. Which would be more effective, a wide or tall fire box. ?
I can deal with the door when I need too. X brace and I've considered using the door as a domestic water preheater
Maybe horrible ideas but....
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I would think tall would be better than wide, a tall firebox would capture more heat if the stack exit was kept lower.
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That's what I was thinking too, but wondered if the larger surface area on top would help transfer heat.
I'm thinking that I'll go 48" high as it gives more room above the stack to catch heat.
Was hoping to start welding this week but may have to wait a couple of days while we wrap up buying some land.
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I'm thinking about a 10" stack. I assume that would be large enough? But again, is too big worse than too small? Would 8" be plenty big?
I want the large firebox more so for longer burn time vs huge heat right now.
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Look at commercial units and compare them to what you want to build, I'd think a 8 would be plenty. A 10" isn't quite double in volume.
Just how many BTU's are you shooting for?
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Well I honestly haven't done the math. I would guess I'll need 100000 but to heat the house or so. 1600sqft new construction. But would like to be able to heat the barn too. So we'll honestly I just don't know.
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My house is fairly poorly insulated, 1750 sq/ft, and,, in a wind tunnel. I keep it 70-72, and I also currently heat 2 rooms in my shop, about 16x16 each, to 65-72 constantly (these are also rather poorly insulated). Plus I run my hot water from my boiler.
I couldn't really tell a difference in wood consumption when I added the shop heat+water heater. It hasn't dipped down into "cold" weather since I finished the shop heat, time will tell I guess.
Heres a link to my boiler build.
http://www.outdoorboilerforums.com/viewtopic.php?f=2&t=53 (http://www.outdoorboilerforums.com/viewtopic.php?f=2&t=53)
As a quick overview, 8" stack which is plenty, Tall firebox (actually dont recall dimensions, would have to look- as a guess 48"x26x32)
Plan, design, and plan. Getting it right before you start welding will save you alot of time.
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Well I honestly haven't done the math. I would guess I'll need 100000 but to heat the house or so. 1600sqft new construction. But would like to be able to heat the barn too. So we'll honestly I just don't know.
How close is this forced air unit going to be to the house and barn? It gets more difficult (and expensive) to move air (and return duct it) very far from the furnace.
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I'm planning on 8 to 10'
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I'm planning on 8 to 10'
You may have already but if not you should check with your homeowners insurance, most have rules on how close the furnace can be to any structure and some will not allow ANY homebuilt unit. I had quite a tussle with my insurance, they actually cancelled me until I proved to them I did exactly what they told me to do...PITA.
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To clarify, in the post above I was talking about insurance issues with our homebuilt AIR furnace, which we used for 4 years until we built our boiler last year.
Had no insurance issues with the homebuilt boiler, it is 50' from the house.
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I'll definitely ask about that once the house is built. But around here I've seen forced air wood furnaces inside attached garages ducted into the house. But it's something that I do need to look into once the house is built.
Worst case it can heat the barn.
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Ok now that we're just about done signing stuff and talking to every government agency known to man, I may fire up the welder soon.
Should I use a different wire or shielding gas for the firebox? Or just standard. 035 mild steel wire? We are already running mixed gas (diamond shield or something they call it from Praxair )
I only wanna do it once.
I'm thinking I want the blower to force air around the firebox a crossed the long side of the firebox. Instead of along the length. Giving more time and surface area to heat the air.
But also considering 3 smaller blowers that could blow long ways and be turned on in stages.
The latter thinking, in my overly complicated mind, the blower handling the actual top of the firebox could handle keeping the house warm when it's warmer outside. And that may keep the fire stoked up a little better so it doesn't smolder out. Then the other 2 would be wired together to come on when the furnace is running full tilt and the one blower can't keep up.
Effectively It sounds more efficient to do multiple blowers. Less energy, a constant good fire (I don't want my wife to have to relight at 2 am when I'm out plowing ) and progressive heating ability.
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Far as wire goes any brand of ER70S6 will work fine, get a roll of the non coated, less splatter.
I run 75% argon/25% CO2.
If your welder can handle it go with .045 for higher deposit rate.
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Ok. Looks like Friday I'll get to start welding. I'm hoping to get the fire box at least tacked up in shape and size. And the chimney in.
I'm thinking half way down the firebox. But is there a rule of thumb on that?