All our air to water heat pump installations require buffer tanks and it is also a common option to pre-heat domestic hot water using indirect tanks.  Traditionally buffer tanks for closed-loop hydronic installations are made from carbon steel while indirect tanks used for potable water are made from stainless steel.  The larger the tanks or more coils they contain the higher the price - something that was driving the cost of installations higher than we would like to see.  The solution was designing and bringing in our own competitively priced line of 316L & Duplex stainless steel water tanks, starting with 80, 105, 120 & 200 USG 4 port buffer tanks and single coil 40 USG and double coil 120 USG indirect tanks.  Our latest innovation in this product category is a pragmatic solution to reducing domestic hot water heating costs without the high complexity and cost usually associated with doing it properly.  It's a 120 USG Stainless Steel tank with an internal 40 USG tank resulting in 80 USG of hot water buffer storage and 40 USG of preheat for DHW - all you need to do is connect your 3/4" potable cold line into the bottom of the inner tank and feed the preheated water to a conventional tank or tankless heater.  In summer chilled water mode the buffer tank will not preheat DHW but instead uses economizer mode by pre-cooling chilled water tank with incoming cold potable water; alternatively you may choose to use two buffer tanks or bypass the preheat in summer.