Some background here: I live at 8300' in the mountains of Colorado. I purchased a house late 2015 that was built in 1992. It has radiant in-floor heating (concrete slab), 865sq/ft lower level, partially subterranean. Upper floor is also 865sq/ft heated by baseboard radiant.
Recently my Superstor 60gal (SSU-60, installed in 2009) indirect dhw storage tank started leaking around the aquastat well. I replaced the well and that didnt solve the issue. I suspect a pressure surge from the town water supply, faulty PRV, and years of improperly configured zones/pumps (overheated water in storage) caused the premature failure.
The tank was recently replaced (same unit, updated design with permanent aquastat well) and I set out to educate myself on the specifics of my setup. I put together this diagram to help me understand the existing system and use this knowledge to update and expand it. My plan is to add a ~700sqft attached garage with in-floor radiant slab, also a ~700sqft studio above the garage with in-floor (staple up) radiant. I intend to have one boiler and one storage tank for the whole structure.
1) Living space ~2400sqft, 4 zones (pex slab lower level, staple up in-floor upper level)
2) 700sqft garage, in-floor radiant, seperate zone kept ~50F in the winter, ambient temp avg 20F
3) One Nest thermostat per zone, total 5
4) Taco ZVC406-EXP-4 OR Tekmar 306V (DHW Priority is important, also Post Purge into DHW tank)
5) Variable power Grundfos Alpha2 pumps (see #6)
6) Tesla Powerwall grid-charged for backup power to the circulator pumps during (frequent!) 1-12hr power outages
Right now, my primary concerns are 1) when DHW is calling, hot water flows through the primary pump and heats the floors, even when the pump is off and in-floor isnt calling. This causes two reasonable-length showers to take 2-3hrs of boiler time to recover. 2) related to 1, in the summer my floors are heated even when the thermostat isnt calling 3)
Any feedback would be much appreciated, including boiler sizing, zone controller (taco vs tekmar), variable power circulators, storage tank sizing, etc etc.