I have a Heatmaker 130HWLP propane boiler, and am considering adding a hot water tank. Should I get an indirect hot water heater and run it off my boiler, or should I get a direct gas water heater (it would have to be a power-vent tank, because there is no chimney downstairs). Which is more efficient, and which heats water faster? Thanks!
An indirect water heater has the advantage of not requiring venting. The boiler you have with a 40 gallon indirect will create 100 gallons of hot water in an hour; this should be sufficient, if not, you can get a very large one and store more. Usually the indirect water heater has more insulation than a gas-fired water heater. You can read a design discussion of the concept at: http://www.hydronic.net in the Lessons section.