I've looked at the outdoor wood furnaces from
Central Boiler. It is a multi-day burning "shed" that gets heat to your central air and water heater via insulated pipes. This seems like the easiest retrofit for wood burning in a house not designed for it. I wonder if it would be hard to use the same loop for going through the solar water heater to do hot water only in the summer, without wood burning, and assist with pre-heating the return in the winter. The price is a little steep, at about $5k to start.