I am trying to help my father choose a new oil fired hydronic system. He has spoke with 2 different companies, one suggest buderus with stackable tank and other system 2000. He is confused which way to go... He lives in cold northern Maine but is south in winter burning about 1100 gallons a year. 2 people live in the home for hot water use. He currently has propane storage. Nobody has suggested an on demand water heater. Any thoughts on the systems or indirect vs on demand?