Got the Email today from Jotul.. a little cut and paste. "We've conducted a test of some of the biomass bricks available as fuel for woodstoves that are currently available on the market. The results of the test indicate that there is a likelihood that over firing of a Jøtul woodstove can occur with the use of biomass bricks as a fuel in Jøtul woodstoves. Jøtul recommends the use of seasoned natural cordwood as fuel for it's wood-burning products. If you sell these products please be aware of the potential for over firing."