one idea I like is to use the very top port as a supply to an indirect water heater only (and an air vent, of course). It is often the case that the lowest usable supply temperature coming from the tank is a function of indirect water heater performance, not space heating. This is especially true with low-temp systems like radiant floors. You might, for example, have to re-charge the thermal storage once it gets down to 120F in order to be able to make domestic hot water. However, if you have radiant floors, you might be able to heat well with 100F supply. By leaving the hottest water "stranded" at the top of the tank, it is available for domestic hot water production while the rest of the tank can continue to be drawn down by space heating.