I had a sneaking suspicion about that. How can my 40k BTU/hr pellet stove possibly heat as effectively as my 120k BTU/hr boiler running at 84% efficiency? Then I thought about the way the EPA calculates efficiencies for pellet stoves. How can they take into account exchanger efficiency in one case and not the other?!?!?! Just goes to show you can't trust those numbers. I can imagine some meeting at the EPA..."If we calculate it that way, nobody will qualify. Better change the calculation then.."