Water heating using descending gases

I think i have a way to heat water in a separate tank using the descending gases. Oil fired boilers in the UK often blow the fire up through a square steel water jacket tube (30cm x 30cm x 100cm) with baffles. I found one at the scrap, removed the baffles and the base and have what could be a great riser chimney that i think would work as a water heater if lined with insulation and then with the thin heat bricks as the actual riser chimney. As the secondary combustion gases descend the outside of the water jacket will pick up the heat and once hot set up a thermal siphon to an adjacent hot water tank. The chimney encapsulation will be made from brick and a fire mortar mix to allow the flow and return pipes to be built in using 300C silicone sealant. The tank is vented. The top will be a steel plate from an old range for cooking on. There will also be a small radiator on the return loop to shed excess heat. What do you think?

Nick Waitz : Welcome to Permies.com,and a Big Welcome to the Rocket and Wood Heaters Forums/Threads, with over 20,000 fellow members you can come here 24 / 7
and usually find someone who wants to talk about what you want to talk about ! You will find that your fellow members bring widely, even wildly different experiences and
points of view, I learn something new every day, both here and at our sister site richsoil.com

I always find it very interesting dealing with those fellow members who live, or have lived outside of the United States, and who pose questions here at permies.com .
Here in 'The States' we take our super abundance for granted !

I have no experience with The type of oil fired water boilers you describe, can you send us a sketch or a couple of pictures before and after ?

I am sure that the best place to take off excess heat energy for water heating purposes would be as the hot descending gases reach the lower end of the barrel, and I am
glad that you so clearly mentioned that your hot water holding tank is vented ! With a large enough water jacket you should never have to worry about your water ever
flashing to steam, because of this risk, usually referred to here as 'Boom, Squish' we have little anecdotal evidence relating to the smallest size of tubing that will support
thermo-syphoning over what distance, somewhere within the Solar hot water community this information should be generally available, and deserves a Forum Thread of its
own ! Good luck with your investigations !

I have been told that non-vented boilers fired by solid fuels are banned in the U.K. It often seems that the two biggest problems we deal with here at Permies are members
exposed to the crap on You Tube who want to build Rocket Heater like devices entirely out of steel, and then want to construct a pressurized boiler for their radiant -heat
floored Air Castles !

Sorry I did not mean to turn this into a rant ! Welcome Aboard ! For the good of the craft ! Think like fire, flow like a Gas, Don't be the Marshmallow ! As always, your
comments and questions are solicited and are Welcome ! PYRO - Logically BIG AL !