What is propane going for in some of your areas? Ben, I can't imagine a $600 month bill for your house. It ain't that big, and it ain't that old. What do you keep it at 85?
At 6-7K for an outdoor boiler it willl take Years of high fuel bills to pay for one. I have one, I like it, but I built it. I no way would pay 7 large for one. Plus, as has been mentioned, any solid fuel appliance is work. People as a general rule, don't like work. I believe we will see a lot of solid fuel appliances for sale in a couple of years. There is a romantic element of "sticking it to the man" that is selling a lot of stoves, the reality will set in for a lot of people soon enough. There is an outdoor boiler called the "Free Heat Machine" oh how I laughed.