DIY vertical wood stove design questions

[TechnoWeenie]

So, I know almost zero about wood burning appliances... But I'm smart enough to realize that there are people that live wood burning appliances and love to share their knowledge, and that's why I'm here...

As with most unknowing people, I have lofty design goals and ideas that will quickly be dashed by reality and expert knowledge..


I have an 8x17 'room' (Military comms van 'box') that needs to be heated, and bonus if I could boil water (should be a non-issue). Insulation is 2" of XPS foam, but with 10 windows, hahaha... yeah..

So, I have a spot that's about 2 1/2' wide, 3' deep, and 7' tall, that I want to utilize to fit a stove in.

I have access to as much steel plate in any size that I need/want, and welding materials. I have all the materials, but none of the knowledge (which is why I'm here)

I have seen small/thin wood burning stoves for boats, which is where my idea came from... But I do have quite a few questions.

I would like to fit a smaller size log in there, whereas most of the small wood burning stoves I've seen (for boats) essentially want you to burn what amounts to twigs..

1. How will a log burning vertically vs horizontally impact heat, burn time, etc.? Is there any reason why burning a log vertically would be a bad idea?

2. As far as baffle systems are concerned, would either of these be good?

The prime concern would be to produce as little smoke as possible, with secondary being to retain as much heat as possible and spread it into the area instead of wasting through the exhaust pipe.

3. I already have an air inlet, a 3" pipe hole... which I plan on using with a foot or so of piping, with a flapper valve/flue control in it as means to control air flow. This way all my air will be coming from fresh air outside instead of using air from inside the cabin area. Similarly, I wanted to to use a flue control setup on the exhaust side as well, going straight up, to retain some heat and retard the burn (?). My concern is that by drawing air from the bottom, and exhausting out the top, all my heat will be lost outside through the exhaust vent, instead of being used to heat inside.

4. As mentioned above, I want this to be vertically oriented, so the logs would be placed and burned vertically instead of horizontally.

5. I intend to use 1/4" steel, and use heat brick to line the bottom..

6. Alternatively, I do have head space to run a 'less insulated' exhaust pipe along the length of the interior, at a slight incline, to allow more heat to dissipate inside rather than outside, but I don't know anything about flow calculations, deposit or condensation issues, etc. or if that would even be needed.


Thoughts? Critiques? Ideas?


I'm just at the beginning stages, obviously, but trying to get a better idea, to make sure it's built properly, and not something that's gonna melt after the 4th time I use it, or dump 90% of my heat outside, or burn through a log in 3 minutes.. :D

 

[SuperSpy]

I'm by no means an expert, but here are a few things to consider:

Cleaning. Everything on the inside is going to get creosote on it, so you need to center your design around every surface on the inside being accessible to a brush of some sort. Snaking baffles like in your #2 design will give you headaches in the future.

Radiant heat. With such a small space for it to live, you're never going to get reasonable clearances from the stove to prevent it from overheating surfaces nearby. What sort of material will it be near? Most normal stoves have a pretty wide exclusion zone around projecting away from any uninsulated surface on the furnace (and inserts are well insulated as to not heat the wall they're mounted in too much). With the stove in such a tight space, you might end up spending a lot of space insulating the surfaces around the stove to prevent autoignition of materials in the room.

Vertical vs horizontal burning is more of a loading issue than a burning issue. How you are going to be constantly fighting the material falling over if it's stacked vertically for the burn. Much easier would be to just cut the wood to length so you can add wood to a partially burned pile.

Ash. I don't see any area to allow ash to accumulate. You should have some kind of shelf/grate for the wood to sit on that allows ash to fall through. Bonus points if you can get a scoop of some sort under it so you can remove accumulated ash without shutting down the stove. This arrangement also greatly improves the burn as it allows fresh air to get under the wood.

Years ago I was mulling the idea of making my own outdoor wood boiler and one thing that really helped me was to look at designs of existing commercial units to see how they differed from the one in my mind to get an idea of things I might be overlooking.

 

[barnaclebob]

Why not just buy a simple stove made for a hunting tent or copy the design of one? They are basically just boxes with a chimney, door, and air control.

If you are looking for efficiency you'll need a secondary air system instead of complicated baffles at which point you are out of the DIY realm.

I'm a DIYer myself but only when the final product will be as good as what I can pay for.

What surrounds the location where you want to put the stove, clearance to flammables is a concern.

 

[Ludlow]

My question is of what value is your time?

 

[webby3650]

I would look at the Jotul combi-fire stoves. They were vertical burners, simple design, and they burned unbelievably clean. Maybe you can copy that design.

 

[Pertzbro]

whats wrong with something simple and cheap?

https://www.northerntool.com/shop/t...edirectid=15379779123640835840110080302008005

 

[bholler]

whats wrong with something simple and cheap?

https://www.northerntool.com/shop/tools/product_200665045_200665045?utm_source=CSE&utm_medium=Shopzilla&utm_campaign=Heaters&szredirectid=15379779123640835840110080302008005,%20Stoves%20%2B%20Fireplaces%20%3E%20Wood%20Stoves&utm_content=52733&szredirectid=15379779123640835840110080302008005

Whats wrong with it? Well it is a poorly designed and very poorly made pos that is dangerous to use.

 

[blades]

Seen more than one of those or copies glowing red over the years.

 

[Pertzbro]

Alright, maybe not that one but you're heating an extremely small insulated metal box. You dont need much.

 

[bholler]

Alright, maybe not that one but you're heating an extremely small insulated metal box. You dont need much.

No but being a small space you need good sheilding and very good control. You dont get that from the cheap stuff.

 

[Poindexter]

www dot permies dot com

See the "rocket stove section", a guy with a PhD from Holland, Dr. Peter somebody is the guy you want to be reading up on. Who knows what he has gotten up to since I was reading his stuff, gosh, five or six years ago.

 

[bholler]

www dot permies dot com

See the "rocket stove section", a guy with a PhD from Holland, Dr. Peter somebody is the guy you want to be reading up on. Who knows what he has gotten up to since I was reading his stuff, gosh, five or six years ago.

I think rocket mass heaters are a good idea woth some promise. But the guys on that site who are associated with paul wheaton greatly exaggerate the benifits and have no clue how modern wood stove work. They also seem to have zero concern with clearances to combustibles.

Again the idea has promise but dont listen to those guys.

To the op i would look at marine stoves. They are designed to safely heat small spaces.

 

[Jan Pijpelink]

Whats wrong with it? Well it is a poorly designed and very poorly made pos that is dangerous to use.

I 2nd that. I had one and I couldn't get rid of it soon enough. If I only knew better before I got it.

 

[TechnoWeenie]

I'll try to answer questions in order...

Construction of the box is steel tubing framework, with xps insulation, and I can face it with whatever I want. Metal to reflect heat, thin firebrick as barrier, etc so I'm not concerned about clearances. Some of the stoves I've seen only require 6" of clearance.. I'd be more likely to use a combo of steel and brick to partially reflect and absorb whole insulating to get the most efficiency and protection.

As far as pre-built ones, the ones I've seen have either been poor designs, sub-par materials, or too expensive.

Baffles and Secondary air or whatever can be designed in but I'm over my head ob the secondary air part, TBH.

My time is worth what it is, part of this is being able to say I built it VS bought it, and save some $.

I've seen the jotul stoves and they look decent but all the reviews I've seen say they crack and while they deliver instant heat they also cool down very quickly, meaning constant stoking/filling to maintain heat.

As far as weight and size, it both is and is not an issue. The box is mounted on a vehicle, but the vehicle is a military 5 ton... Think deuce and a half, then double it, heh. I can't have 3k lbs of stucco and mortar to make a conventional rocket mass heater...

For reference...

That's an M1031 towed behind it for scale, essentially a full size 1 1/4 ton Chevy truck with a service body...


The space is the area seen where the 3 phase breaker panel is on the left, which has been removed...

 

[maple1]

I'll try to answer questions in order...

Construction of the box is steel tubing framework, with xps insulation, and I can face it with whatever I want. Metal to reflect heat, thin firebrick as barrier, etc so I'm not concerned about clearances. Some of the stoves I've seen only require 6" of clearance.. I'd be more likely to use a combo of steel and brick to partially reflect and absorb whole insulating to get the most efficiency and protection.

As far as pre-built ones, the ones I've seen have either been poor designs, sub-par materials, or too expensive.

Baffles and Secondary air or whatever can be designed in but I'm over my head ob the secondary air part, TBH.

My time is worth what it is, part of this is being able to say I built it VS bought it, and save some $.

I've seen the jotul stoves and they look decent but all the reviews I've seen say they crack and while they deliver instant heat they also cool down very quickly, meaning constant stoking/filling to maintain heat.

As far as weight and size, it both is and is not an issue. The box is mounted on a vehicle, but the vehicle is a military 5 ton... Think deuce and a half, then double it, heh. I can't have 3k lbs of stucco and mortar to make a conventional rocket mass heater...

For reference...

View attachment 229993

That's an M1031 towed behind it for scale, essentially a full size 1 1/4 ton Chevy truck with a service body...


The space is the area seen where the 3 phase breaker panel is on the left, which has been removed...

View attachment 229994

Metal not only reflects heat but also conducts it so just facing your insulation with it or the like won't help you clearance to combustibles out a whole lot.

 

[bholler]

I'll try to answer questions in order...

Construction of the box is steel tubing framework, with xps insulation, and I can face it with whatever I want. Metal to reflect heat, thin firebrick as barrier, etc so I'm not concerned about clearances. Some of the stoves I've seen only require 6" of clearance.. I'd be more likely to use a combo of steel and brick to partially reflect and absorb whole insulating to get the most efficiency and protection.

As far as pre-built ones, the ones I've seen have either been poor designs, sub-par materials, or too expensive.

Baffles and Secondary air or whatever can be designed in but I'm over my head ob the secondary air part, TBH.

My time is worth what it is, part of this is being able to say I built it VS bought it, and save some $.

I've seen the jotul stoves and they look decent but all the reviews I've seen say they crack and while they deliver instant heat they also cool down very quickly, meaning constant stoking/filling to maintain heat.

As far as weight and size, it both is and is not an issue. The box is mounted on a vehicle, but the vehicle is a military 5 ton... Think deuce and a half, then double it, heh. I can't have 3k lbs of stucco and mortar to make a conventional rocket mass heater...

For reference...

View attachment 229993

That's an M1031 towed behind it for scale, essentially a full size 1 1/4 ton Chevy truck with a service body...


The space is the area seen where the 3 phase breaker panel is on the left, which has been removed...

View attachment 229994

You have xps insulation which is extremely flammable so you really really need to be concerned with clearances. Yes there are stoves designed by engineers and tested extensively that get down to 6" or even less. But yours will legally have 36" clearances. Which can be reduced to 12" with a proper ventilated sheild. Jotul stoves really are top quality those complaints you heard are most likely due to operator error. But they are cast iron which is not cheap. And they are all going to be way to large for your space. You need to be looking at stoves designed for small spaces like marine stoves or tiny home stoves.

 

[bholler]

In your list of concerns you top one should be to not kill yourself. This could happen with fire, fumes from the xps foam, or co poisoning. The other things are very minor concerns compared to that.

 

[TechnoWeenie]

Fresh air from outside = no concern of hypoxia.
Sealed combustion chamber, direct exhaust outside, and CO detector = no concern of CO poisoning.
Small burn chamber, possibly double walled with small fan pushing air around the outside wall would drastically increase heat output and lower Temps on the outside. But I'd have to figure out what thickness and distance the outer wall should be. I could also stick with single wall and use a fire brick as insulating material on the wall of the box body.

I understand I haven't explained my background, but 'idiot' isn't part of it..

 

[Pertzbro]

If this is mounted on a truck, I wouldn't waste any further time or effort and just go propane heat.

 

[showrguy]

Fresh air from outside = no concern of hypoxia.
Sealed combustion chamber, direct exhaust outside, and CO detector = no concern of CO poisoning.
Small burn chamber, possibly double walled with small fan pushing air around the outside wall would drastically increase heat output and lower Temps on the outside. But I'd have to figure out what thickness and distance the outer wall should be. I could also stick with single wall and use a fire brick as insulating material on the wall of the box body.

I understand I haven't explained my background, but 'idiot' isn't part of it..

How old are you ??
Just curious ..

 

[webby3650]

I've seen the jotul stoves and they look decent but all the reviews I've seen say they crack and while they deliver instant heat they also cool down very quickly, meaning constant stoking/filling to maintain heat.

This is not a good representation of any Jotul stove. They are high quality stoves! Iron does not make instant heat, nor does it cool down quickly. They produce good solid burn times. I don’t think a Jotul would be good in your application, but it’s a solid product.

 

[bholler]

Fresh air from outside = no concern of hypoxia.
Sealed combustion chamber, direct exhaust outside, and CO detector = no concern of CO poisoning.
Small burn chamber, possibly double walled with small fan pushing air around the outside wall would drastically increase heat output and lower Temps on the outside. But I'd have to figure out what thickness and distance the outer wall should be. I could also stick with single wall and use a fire brick as insulating material on the wall of the box body.

I understand I haven't explained my background, but 'idiot' isn't part of it..

I never said you were an idiot. But i have seen lots of pretty smart people do really stupid things. You also cant rely on a fan to keep the outside temp low enough to be safe. What happens if you loose power or if the fan dies? As far as co goes what detecor will you be using? And how do you plan on sealing everything including pipe joints well enough that co could not escape? You will be running a very short stack wich means relatively low draft. That increases the risk of co when the fire burns down. I will agree that outside air all but eliminates the risk of hypoxia which is why i didnt mention that. But the other issues are still very real concerns.

 

[bholler]

Even with double wall construction and firebrick i would not go below 12" clearance to combustibles.

 

[blades]

firebricks inside stove- besides the bit of insulation/shielding of burn chamber walls, primary purpose is to reflect and retain heat in the burn chamber to achieve temps high enough for secondary combustion- secondary combustion can be built rather simply - air intake for 2nd burn to a tube being preheated by fire then 1 or 2 tubes across top of fire box with a bunch of small holes cross drilled ( 1/16-1/8) along its length- above tubes should be a baffle of some sort covering almost all of the top area ( horizontal) of the burn chamber - at the short end exhaust gas flow up into the remainder of the burn chamber and out the flue pipe- generally a baffle is placed in front of the flue exit in the exhaust stream-, another way is to use a catalytic converter ( just like on a car) to burn residuals before exit- that exhaust can reach some 4 figure temps so a heat exchanger ( simple large chamber)area is utilized to draw off heat before exhaust exits unit. Very basic descriptions

Back a bunch of years ago many retrofitted units with simple 2nd burn systems - the involvement of the EPA in stoves really snuffed out a lot of interesting designs due to the cost of getting certified.

Vertical stoves are more of a external appearance than operation- closet thing to a true vertical burn would be the classic rocket stove design- burn up center from fuel at base hits top hat deflector travels down outside burn tube then exhausts at about the same point as the base fire. the initial design was for cheap fast cooking heat as such it is not a long time heater hense the mass function to absorb heat from exhaust stream and slowly return same to area.

it would be possible to use a rocket type unit and use water as the thermal storage by making a subfloor and running piping under that possible it could operate as a thermal cycle system bonus is hot water for whatever.

 

[bholler]

firebricks inside stove- besides the bit of insulation/shielding of burn chamber walls, primary purpose is to reflect and retain heat in the burn chamber to achieve temps high enough for secondary combustion- secondary combustion can be built rather simply - air intake for 2nd burn to a tube being preheated by fire then 1 or 2 tubes across top of fire box with a bunch of small holes cross drilled ( 1/16-1/8) along its length- above tubes should be a baffle of some sort covering almost all of the top area ( horizontal) of the burn chamber - at the short end exhaust gas flow up into the remainder of the burn chamber and out the flue pipe- generally a baffle is placed in front of the flue exit in the exhaust stream-, another way is to use a catalytic converter ( just like on a car) to burn residuals before exit- that exhaust can reach some 4 figure temps so a heat exchanger ( simple large chamber)area is utilized to draw off heat before exhaust exits unit. Very basic descriptions

Back a bunch of years ago many retrofitted units with simple 2nd burn systems - the involvement of the EPA in stoves really snuffed out a lot of interesting designs due to the cost of getting certified.

Yes it may have snuffed some. But it did make stoves on the whole work much much better. Yes there were a few companies working on clean burning and efficiency before epa regs. But i guarantee that without those regs the majority of stoves on the market would still be basic smoke dragons.