Low Pressure Wood/Biomass Steam Boilers?

I was just wondering if anyone has any experience with, or information on, low pressure steam boilers that use wood or biomass for fuel. A quick search on google brings up several companies producing large wood fired boilers for industry and electrical generation, but nothing on the small side (less than 20hp). If they exist, I would be interested in learning more and trying to price and source one. My requirements would be a minimum of 350,000btu's output but not more than 500,000btu output. Can systems like this (if they exist) be run inside a building? Anyone know of anything like this?