We are working on a simple pellet boiler that is passive. No pumps, augers, or fans. It would gravity feed into the burner and dump all the heat into a tank. The concept would work best with smaller houses or homes with small heat loads. Obviously, it is a batch fed unit that has to burn out the load put into it, but that keeps it simple and hopefully, inexpensive. A lot of work has been done on this, this is just our spin. Here is a video of our first trial which was made of sheet metal and worked pretty well. The full boiler is in the works and should be in my hands in a week or two. It is similar to the stick wood unit that we did a couple years ago.