Having a new geo system installed, a Waterfurnace 7 series and need to figure out how to configure water heater(s). The install guide for waterfurnace suggests best results for using the DSH is with a buffer tank and I have read that elsewhere on this forum. I currently have an oil boiler hydro system that provides heating but also supplies hotwater through an indirect buderus logalux ST300 (80 gal) which I think could work as a buffer tank. This tank is ~10 years old but appears to be in good shape (given I can't see inside its plastic shell) and have had no problems with it. This tank has always provided enough hot water. I have read in other discussions that in northern climates, it is better to have a smaller 50 gal buffer tank than a 80 gal tank. But I already own an 80 gal tank that i think (need to confirm) could be used as a buffer tank so a few questions: Question 1: For a buffer tank should I: A. Use the buderus 80 gal as unpowered buffer tank since i already have it or B. Ditch the 80 gal and get a conventional 50 gal water tank as a buffer tank - efficiency of 50 gal over 80 gal out weights the fact I already own the 80 gal and it is 10 years old Question 2: What size finishing tank? - 50 or 80 gal? I am thinking 50 - having a buffer tank plus a finishing tank of 50 will provide the same or more hot water as the 80 given normal use for a family of 4. Question 3: What type of finishing tank - conventional or hybrid/heat pump? (I have heard that finishing tank electric use can be so low that getting high efficient model might not justify extra purchase cost) Question 4: Or should I scrape the buffer tank and just install one 80 gal hybrid tank? Any thoughts / suggestions and reasons appreciated. Thank you in advance.