Abstract
Reason of reducinng boiler-efficiency on low-load was analyzed, it became obvious thatit is mainly radiationloss. Then, the best way to be kept high efficiency on low-load is buildup of insulation. But, in case of it is difficult, high efficiency on low-load can be gained by equipping additional cooling-surfaces, for exanple, economizer or air-preheater. If fan is not replaced in this case, available load is limited. This report explaines these calculation.
