[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.