Component failures and system performance degradation in SHW systems due to scaling are common in areas with hard water, it appears that many valve and pump failures on the potable water side are related to scaling, and any scale build-up on heat transfer surfaces will result in performance degradation. Different designs are compared in regard to their suscepribility to problematic scaling. Indirect systems utilizing external and tank wall heat exchangers are compared in regard to the rate of scaling and the consequences of scaling on system performance. The tank wall heat exchanger appears preferable over a doubly pumped external heat exchanger, both in terms of system reliability and resistance to performance degradation.