I'm interested in learning regarding the feasibility and advisability of using a hybrid "small tank" condensing or tankless condensing hot water heater to provide both DHW and space heating for new construction in a heating climate. Examples include Navien America 180/210/240 (EF .98-.95), Eternal GU195 (EF .96), Takagi TH2 (EF .93), Rinnai RC98HP (EF .93), Quietside ODW199 (EF .92), or Noritz NCC199 (EF .92). Alternative configurations could be desirable: a)circulator with a fan coil in the HRV duct; or for higher heat load b)circulator with baseboard hydronic distribution (easy to zone); or c)maybe both with priority to the HRV fan coil. First priority goes to DHW and no potable water used for space heating. Advantages could include high efficiency, avoid the cost of a separate furnace or boiler, and compact form factor. Any advice or experience re is this possible, initial cost, long term reliability, availability of aftermarket service and parts, longevity?