I have a Jensen Wood or Coal indoor boiler. It attaches to my Oil Boiler. It is the bigger model (100,000 BTU I think) is holds 24" logs easy. We only stoke the fire 3 or 4 times a day. (morning, noon, dinner, bedtime) It self regulates the temperature.
We used 0 gallons of oil this winter. We burned about 3.25 cords heating our house and domestic hot water. We keep the main part of the house (kitchen, dinning room, living room) at 70 and the rest (all the bedrooms and bathrooms) at 68
I added a switch to my oil boiler so I can actually turn off the burner but still let it control the circulater pump and zone valves.
I would not want an outdoor boiler because I wouldn't want to have to go outside and stoke the fire. It is nice to walk down in the warmth in my underwear and check the fire. Plus the heat the boiler sheds warms my basement and that heat rises up through the floor. The main living area zone rarely kicks on.
I would not trade my indoor boiler for anything. When I move I will take it with me.
I have helped two others install Jensen boilers and they agree you couldn't pry it away from them. You can buy them used for about $600 in excellent condition.