Thanks for the welcome and the replys. Here is a little background info. I live in SW lower Michigan, and have been heating my 3000 sq ft house and dhw, with a Hawken boiler for 5 seasons now. Overall I am happy with my boiler, but I use a fair amount of wood in a season (between 10-12 full cord from Oct-May). Part of it is because we keep the house at 73-74 most of the time but hey, thats what I bought it for. I think the design of my boiler is similar to a "standard" heatmaster and I was just wondering if there was a simple mod to make to mine to make it perform like the "e" model. If the increase in effeciency comes from a double pass chimney I guess I am out of luck. The design of mine forces the gasses over water filled tubes which go across the top 1/3 of the fire box, then up again and back through a channel above the tubes along the very top of the fire box. At the time I was looking at boilers this seemed like one of the better designs for increasing heat transfer, as the tubes effectivly increase the surface area of the water jacket/firebox. When the boiler is cycling there is no visible smoke from the stack, only heat waves. Sure would be nice to be able to capture more of the heat escaping from the stack.