Closed loop woodstove powered water heating loop

The reason they have it on an open loop set up is temperature and pressure.
Solid fuel has no way to be regulated. Its not like electric, gas or oil. In those cases you turn off the fuel and no more heat goes into the system...cant do that w/ wood solid fuel.
If you close up and pressurize the system in effect you have created a serious bomb.
Water when heated and pressurized is a VERY powerful force.
Just look up watts water heater explosion videos on YouTube.
Please dont do this...

Hi, I just saw the diagram of an "open" system. It doesn't look that way to me. Open would have a vented pipe or tank at the top, so that pressure could never build up over the pressure created by the vertical column of water.

Yours, Larry

That diagram is a catastrophe waiting to happen. Not only is it a closed system -- I can't even find a pressure/temperature relief valve on it -- but it mixes the radiant loop heating water with the domestic hot water. If it doesn't blow up the bacteria will make you very sick.

Now. That is to say that you can't do what you want to do, but not exactly in the way you describe it.

First place, what exactly is an open system? As the name implies, it is a system which is, in fact, open to the atmosphere -- the easiest way to do that, assuming there is a tank on the system somewhere (there will be -- see below!) to have a good big vent on that tank -- for a wood stove as the heat source, I'd be inclined to use 2 inch black iron pipe going straight up, then turning over at the top with the outlet -- unobstructed -- pointing down. The purpose of the vent is simple: when the wood stove gets carried away (which it will, trust me) and starts boiling the water, you don't want any pressure to build up at all, and the vent will allow the steam to escape without building any pressure.

Now I mentioned a tank. Your primary loop water capacity is way too small. So, the next thing you need -- on the part of the system connected to the wood stove -- is a tank big enough to absorb all of the output of the wood stove for a reasonable time -- which I would say would be the maximum burn time of a fully loaded stove. There should be some water left over at the end. So... take the rated output of the stove (which you can likely find somewhere stated as BTUh) times the maximum burn time in hours and multiply -- that gives you the number of BTUs which you are trying to absorb. Divide that by how much heat you can get rid of in terms of steam, which is about 7,000 BTU per gallon of water. That gives you gallons. Double that, and that's the tank size you need. That tank should be set up so that it is above the wood stove (any water left below the wood stove won't be usable -- don't count it) and can be hooked up, as you suggested to thermosiphon.

You can tie your sidearm domestic hot water heat exchanger into that thermosiphon loop very handily.

Do not use any glycol in the system. As has been noted, the stuff cokes when it gets too hot -- and it will. Use only water. If you are concerned about freezing -- and living in Alaska, I can see you might be -- arrange your piping with a drain for the tank so you can dump it if you anticipate freezing for some reason.

Someone mentioned using the heat rejected from the diesel engine, assuming you plan to use it from time to time. And why not? There is no good reason why you can't hook it's cooling system up to that nice big tank I mentioned above. You could have a conventional radiator hooked up in parallel, with the circuit to the tank. To prevent overcooling the diesel, though, both those circuits need to have the usual bypass and thermostat arrangement. That would take a little ingenuity, but would work; the only down side is that most automotive diesels these days are designed to run at around 195 Fahrenheit, so you would need to arrange your engine thermostats to maintain that. I can't say I'm much of a fan of the idea of a heat exchanger on the exhaust, though. First place, there really isn't that much heat there (yes it's nice and warm -- but there aren't that many BTUs available) and unless you bought a marine dry exhaust exhaust cooling heat exchanger -- which would be pricey -- you have a very real risk of creating an unwanted carbon monoxide source for your building.

Keep asking questions!

A simple 'on-demand system' for domestic hot water is just a pot sitting on top of the woodstove. Compact, no risk of explosion, easy to monitor, easy to clean. Plenty for doing the the dishes or making tea.

For baths & showers, you could just trickle water through the boiler attachment and directly into the tub, with no extra storage tank. Just make sure there isn't a second valve (after the wood stove) that could allow pressure to build up.

I put a Cubic mini wood stove in my TC. It heats nicely with a couple of dielectric fans, and can also be used for cooking. Tried a few versions of a water jacket without much luck. Even if you get the pressures under control, you end up overheating the space before you have enough hot water to shower

The RV industry has quite a few options for heat and or hot water generation with LP, diesel, or gasoline fired units.
Here is a company that supplies some of the RV manufacturers. For the amount of DHW you need I would consider the truck fuel as your DHW heat source.

Some of the former long hairs here may remember the gasoline powered heaters in VW microbuses