Batch Box Outdoor Wood Heater idea

Ok, here's another idea that I'll never get around to but it might possibly change the world so I'll throw it out there.  If you make it, sell thousands and get rich, please send me a small cut of the money :)

Batch Box Outdoor Wood Heater

In my part of the world, people pay a bunch of money to install an outside wood boiler that heats water and sends it to their house, shop and garage for heat.  The mess stays outside and it can't burn down your house.  But they sit there and smolder a lot of the time and smoke out the neighborhood.  They also consume about double the wood of a normal wood stove.  They also rust out or die after about 10 years.

What if someone made a 8-10" batch box that heated up a liquid mass.  This liquid wouldn't be water, maybe an oil or other liquid that could handle some real heat.  The liquid could either be pumped to the house for heat, or water could be pumped through the liquid mass to heat up and then heat the house.  With enough mass (500 gallons?), and a big enough batch box, it might only need to be lit and loaded once a day.  

No smoke, efficient use of wood and fewer insurance/code issues to work through to implement.  Wood boilers are already big and heavy so delivering them is a process.  Manufacturers could make them and use their existing supply/sales routes.

Hi Mike;
Well, it sure could / should work but it would take quite a bit of work and a fair amount of money.
A ten-inch batch and all the things needed to build it.  
A 500 gal. tank filled with an oil. I would use hydraulic fluid myself, used if I could find it in a shop.
A building heavily insulated to hold that heat. Piping to move your fluid to the house.
Having electricity, of course, is crucial for pumping.
A house system with radiators...

I'll stick with a batch and a bell but maybe someone will refine this and make a million bucks!

This is something I want for myself.
I've been scheming on it for years...

Note that many comercial stoves could burn much cleaner if they were run properly.
If we throttled back a rocket stove it would also burn dirty and inefficiently.

My first exposure to thermal mass plus wood burning was  a guy who kept his of grid cabin warm all night by burning a hot fast fire in a barrel stove.
Said stove was in the un-insulated cellar of his cabin, and happened to be surrounded by many tons of creek rock that he had piled on and around it.

I say all of this to suggest that what is needed most for outdoor wood burning boilers to be cleaner and efficient is indoor mass in the form of vast amounts of water.

For reasons of economics, I want to use water as my heat exchange medium and for other reasons of economics, I want to boil off the water and condense it inside.


5000 gallons of water is roughly equivalent  10 to 11 water heaters in one's basement.
Not unreasonable and more importantly,  not expensive.
Ganged together with PEX, the whole set up could cheap.
PEX has tempature rating that is close to 212F, but that is under mains pressure.
Lowering the pressure will up the rating and I want an unpressurized system anyway.
Rather than adding radiators in each room, one heat exchanger in the return air duct of my forced air furnace should do.
When the thermostat calls for heat, the furnace would turn on the the fan, drawing air across the heat exchanger.

For reasons of easy use and stacking functions,  I've decided my heat source should be one that produces charcoal.
I've three in mind, only one of which I've tried out.
That's the boiler powered by a tlud that burns woodchips.
It's the one I see my wife being willing to use.

The other two are a design from DriveOnWood and a weird version of a pocket rocket.

The last house I lived in, had an outdoor boiler and, as you mentioned, it smoldered away most of the time.  I have also thought that a batch burner of some sort would work well.  I would use antifreeze and water mix just like a car rad., which is what I used in my last boiler.

William Bronson, there's a lot of DIY tank options, which are a more efficient use of space, and probably less expensive per gallon than water heaters. Take a look at builditsolar.com for examples.

Mike Hassl, If you are using oil to exceed 212*F, then you are looking at needing a steam heating system in the house? or just trying to heat a non-pressurized water storage tank? I'd also be happier to circulate water or glycol mix than any petroleum oil; veggie oil maybe, but I think that has mobility issues. I'm thinking of two things... "boom-squish" and deep fried turkey fires.

I think William's massive water storage is a good idea, it can also have a solar hot water collector as an input, domestic hot water as an output, and built under a house the heat losses are reclaimed somewhat.

I don't know of anything less toxic, more available, or more efficient at storing and moving heat, than water.

My thinking along these lines is that you need to heat up a large masonry/cob mass and have a network of copper tubes embedded in the mass that can pick up the heat and move it to wherever you want to pump it to.  Not a thermodynamics guy but there should be sweet spot between how much mass you need to warm and how much water you need to heat to warm x amount of space.  Of course you'd want to insulate that mass as you probably don't want to lose the heat to the environment.

All this of course predicated on a careful analysis and dutiful respect of the boom squish risks involved.  I think embedding the water lines in the mass reduce this threat greatly.

I love builditsolar but I think you are confused, I was talking about using free junked waterheaters.
These are commonly available as scrap, indeed one local plumbing supply house has 20 plus available for the asking at any given time.
They usually have 4 openings threaded in 3/4" npt and rarely have a leak that is detectable.
They are insulated,  but they could certainly use more.

Since we are only paying for the connections, I think they are the cheapest water storage option available.

William, not confused. 10-11 water heaters definitely sounded like it was a salvage operation! Yeah, not all water tank replacements are leaks, sometimes bad heating elements, replaced at end-of-warranty but not failed yet, or system alterations (fuel to electric or to tankless). A courteous plumber might even write a note as to why it was taken out on the tank...
I was merely commenting on the home-built tanks being more space efficient, and seemingly easy to make heat exchangers with just coils of PEX inside.

My thinking with oil for the mass is that it doesn't boom/squish as badly.  I *assume* that the regular wood boilers spend all that time smoldering so that they keep from overheating the water past 212F or so they stay lit until the next time some heat is needed.

I'd probably prefer to transport the heat with water (like a normal outdoor wood boiler system).  Ideally, this new device could take the place of an existing, worn out, boiler and use the water/antifreeze circulation system that's already there.  

The mass could certainly be something like rock/cob/pebbles but then getting the right amount of heat to the water becomes tricky.  If you're circulating water through a solid mass the only adjustment you have is how fast the liquid moves through.  And the heat has to transfer within the mass to the liquid.  With a liquid mass you can pump some into a smaller tank with a coil of antifreeze lines running through it.  Let's say that small tank has a target temp of 160-180.  When the tank temp drops below 160 just pump a bit more hot oil into the tank until it gets back up to 180.  The antifreeze going to the house is pumped based on the house thermostat.  The hot oil going into the heat transfer tank is controlled by its own thermostat.  All that's left is to light a batch box every once in a while.  The oil mass could be sized to handle two firings of the batch box so if you foresee a cold night you light one at dinner time and go put more wood in before the coals are gone a few hours later.

Maybe there are better ways to control it or do this, but that's what pops into my brain.....

Oh, you are thinking to keep the mass outside and move the heat inside on demand.
Oil does have an advantage on how high it can be heated.
You will need a very insulated enclosure,and you might need a pump that can handle high temperature oil.
You might be able to skip the pump  and use a convection loop, and/or some boiler valves.

And here is the hot oil pump you are looking for!
https://permies.com/t/33523/world-famous-SBC-pump
You can run this with a cordless drill if you needed to.

Yes William, that's it exactly.  The current wood boilers are insulated and I suspect they have a decent amount of water as their mass.  

This would be a unit that contains the batch rocket, the mass (oil?), the heat exchanger (oil? to antifreeze/water), pumps and insulation.  Weather proof and delivered with a truck and a forklift.

I think they generally have a water jacket or boiler tubes, but not a mass of heated water.

I think your rocket boiler would live nicely at one end of a hoop house filled with dry/ing lumber.

Just thinking about some of these concepts for related reasons with deep winter being so ever-present... :-/      The idea of an outside RMH just seems like so much heat would be wasted, but I could be missing something.  At least in North America, however, a common home configuration is the house-with-attached-garage.  
     
Please forgive the crude drawing and I hope it conveys the important features. With the understanding the building code may not be any more lenient towards a RMH stationed in an attached garage, it would seem a win-win to heat the garage space with the bell-portion of the RMH and let the heat-exchanging u-turn piping....in some as yet undetermined configuration and composition....project into the basement or subfloor region for supplemental heating.  In our current old farmhouse, the previous oil-burner used the surrounding basement air as a large part of its intake air for the forced-air movement of the heat in the ducting.  Our new propane furnace uses an outside air duct for air supply......and cold air it is when below zero degrees F!  Yet if desired, our installer even mentioned that removal of a door on the furnace would simply allow bypass of the air-intake and let the furnace use basement air for the intake.  To be clear, this rather drafty farmhouse allows that kind of air to be used with little concern about oxygen debt.  Nevertheless, my point would be that, with some creative engineering and planning, a fair amount of heat could be brought into the home space via an RMH heat exchanger+ while leaving the RMH bell and combustion gymnastics within the garage space.  Perhaps this has already come up as an option many times before?.....

It just seems that, in the spirit of getting RMHs in front of as many people as possible, this option would reduce home modification (that might depreciate home value among other things) while providing a home-owner with a chance to install an RMH and maximize its benefit to the home, even if not located directly in the living space.