I know people who have both indoor and outdoor boilers. As Dennis said they do consume the wood but they do get the job done in large hard to heat houses or shops. One things that scares me is the total investment can be large with any kind of central boiler system. I would hate to invest about 10K in a boiler setup and then find out for some reason I don't have the health or time to do firewood. Many people report fast payback times with a wood stove. Boilers would take quite a bit longer to break even.