Feedback on new stove sketch for water heating and space heating

Hello Folks, I've hit a plateau on my stove design project. I did this drawing a few months ago and want to assemble a prototype this Summer. I don’t know why it didn’t occur to me to ask for suggestions sooner.  I’m trying to heat my customized Motorhome as efficiently as I can with wood. And heat a trough of water for bathing, washing, and heat storage. The Motorhome space is long and narrow so I was trying to design a long and thin stove that would emit heat to the space on one side and to water on the other side. The trough is flat sided aluminum so I’m hoping to conduct heat efficiently into it from square steel pipe. The trough is going where the couch was lol.  But it will have a insulted lid and cushions for sitting and heat storage.
Im hoping to have the choice of burning pellets or wood. I’m not sure what size to make the stove and tubing? Will it draft? There’s a bypass for starting it. I have some 4” square tubing to try it out but wanted to refine it further first.
There’s some cool things about this design but will it work!? What changes would make it better?. I dislike backdraft inside my Motorhome.
How can I attach the steel to the aluminum so it conducts well? The trough is about 5 feet long. Thanks
 

Does it have too many 180 degree switchbacks?

Hi Jeremy,    Yes, I would agree that there would be a lot of drag on the exhaust that it would more than likely have trouble running smoothly and cleanly.
Also, a 4" system also has a lot more drag due to the boundary layer effect and add to your troubles.
Having 2 separate places to feed different fuels makes it more complex as well.
Instead of all that piping, have you considered making a bell instead? A large chamber (or stratification chamber) puts very little drag on the system and is easy to construct.
As for heating the water, there are lots of posts discussing different ways to do this. Non-pressurised systems are often recommended due to them being more safe and simple for a wood fired application.

Thanks Gerry.
What if I increase the size to 6” and reduce the number of switchbacks in half??! This is the only shape stove that will fit on the side of my tub and in my Motorhome. Maybe I can do a mini bell next to the stove. With a bypass going to the switchbacks?

So if I get this straight Jeremy, your wanting to channel the exhaust through pipes to act as a heat exchanger in a trough of water in order to heat it.
If so, that is not going to be easy to seal the pipes enough to keep them from leaking or rusting and would be a real bugger to clean.

How much space do you have above your stove? If you have some room, perhaps you could make a boiler similar to these ones:
Walker boiler
Rocket Water heater at Wheaton Labs  
Geoff Lawton Rocket water heater
Rocket Stove Water Heater Repair

Your trough then could become a bell bench to have some heat retention.

Thanks again Gerry. What I was hoping is that the stove and flue is attached to the outside of the aluminum tank. I was hoping to heat the air and water in the Motorhome at the same time.
I just realized with my original drawing that gases might build up at the top of the stove and then explode so have done what you suggested and added a Bell at the top of the stove so all gases exit the stove.

Things are becoming more clear now Jeremy. Thank you for the clarity.

Your new drawing is starting to look like a J tube rocket stove but not quite clear as to how well or clean it will run as your design is quite unique with extra bends and restrictions.
Is the door there for viewing the flame coming from the pellet basket (I assume) from the bottom of the drop fee tube?

The split in your piping to make a long and short run will more than likely not work to how you are expecting it to. Exhaust flows very similar to fluid dynamics - water will always seek the shortest path. Therefore, one pipe will prioritize (the short one) and the long one will get next to no draft or heat.  
Also, the surface area the exhaust being in a pipe will have very little contact with the tank so heat transfer would be poor. If you could perhaps design it so that the exhaust is free to flow around the entire surface of the aluminum tank, heat transfer would be greatly increased. I believe this is how most of the links I sent operate using this principle.

Also, when I mentioned adding a bell (what is also referred to as a stratification chamber where the exhaust stream slows down enough to be able to separate into layers - hottest gasses at the top and progressively cooler to the bottom) I meant an open chamber. If the bell you drew is a metal barrel, that certainly will work to shed a lot of radiant heat into your trailer but doesn't really slow down enough to be called a true bell.

Could you provide a picture of the proposed space your planning on using?

That helps. Sorry about my shaky drawing but I think it gets the concept across for the most part.
I need to be able to burn pellets and/or firewood so the door is for loading firewood. And the door is for cleaning and viewing the flame. So it’s a batch box variation.
I was planning on using square steel tubing to maximize the contact with the tank.
There will be a damper in the flue at the bypass junction to close the vertical flue so only the horizontal flue is open. The vertical chimney is for starting only. Once the stove is hot and drafting well I’d close the damper and redirect the exhaust gases into the horizontal flue (heat exchanger) attached to the side of the trough.  
I’ll get a picture but the space is being used for storage currently.
I’m tempted to buy some plans but don’t know if they will help me with this design. It needs to be relatively lightweight because it will be mobile. I’d prefer the steel stove to weigh under 100 lbs so I can use it outside in the Summer. The aluminum trough is about 50 lbs.
Cheers

If you can get or make a steel box of similar dimensions to your aluminum tub, that would be ideal for heat transfer and good draft/low resistance, not to mention cleaning. The steel box should be as tall as you have space for; then hot gases will be able to rise to the top and heat the tub, and as they cool they will sink to the bottom of the box where the exhaust should connect. The steel box would not need to be structural thickness, just sturdy enough to hold the tub, as it will not have super-hot combustion inside it.

Glenn.....I think I am visualizing what you are describing and I like it. I’ll stop dawdling and start doodling some more and see how it looks.
I want to get a clean burn as I can with a steel stove combustion chamber then extract heat downstream in the heat exchanger. It might need to have cleaning ports as I’m concerned about soot and creosote on the heat exchange surface.

Simplified version with a stove design similar to what we have built before. Not extremely hot or efficient The sheet metal heat exchanger is now what I’m concerned about.  
I’m interested in changing the stove to a insulated mini batch box design? If there is a prototype out there I’d like to hear about it? I’m pretty confused on how the ports are designed.