[throwaway4aday]

If you have hydronic heating anyways then why not get a wood fired boiler? They're extremely common where I am. Why would you need to store the heat? A wood fire isn't instant on but it doesn't take that long either plus you get the heat from the stove itself well before the baseboards heat up.

[endisneigh]

I have a pretty high efficiency tankless boiler so it would be expensive and wasteful to switch at this point. It is possible to buy a wood fired boiler and hook it up to the house to supplement the tankless but I'm skeptical that makes financial sense.

[throwaway4aday]

I'm a bit confused since I thought you were talking about hooking up a wood fired furnace of some type. Putting a solid fuel boiler in line with an existing system is pretty common and doesn't have any impact on the system as a whole efficiency wise except for a tiny bit of heat lost to the length of pipe in the boiler when it's not in use but if you don't mind turning valves on and off you can avoid that with some simple plumbing. When I say boiler I'm talking about the heating part of the unit btw, the tank itself is generally separate if you have one at all.

[endisneigh]

my understanding is that a wood furnace is meant to be used with wood pellets or properly seasoned wood. using random rotting decaying dead wood outside probably wouldn't be a great idea - I'll need to look into it more.

[throwaway4aday]

Ok, yes that's true, if you burn wet, green or rotten wood it's going to make a lot of smoke. Wood really begins to rot after the first year if it isn't cut, split and properly dried. If you have deadfall around you that you want to use then you need to process it into firewood as quickly as possible and store it somewhere it won't stay wet.

[acidburnNSA]

Not OP, but biofuel combustion is not necessarily better than gas from particulate air pollution or climate metrics.