Sounds like a good application for an outdoor boiler. Pump hotwater indoors to an HX..
Maybe a DIY version of one of these..
Outdoor Wood Furnace | Affordable Home and Hot Water Heating | WoodMaster
Of course, sooner or later the EPA will fine you $2,000,000 a day..
I hear they carry guns now. And SWAT teams.?.
Maybe Solar hot-water would be safer..