Hot Water Heat Pump
- R410a - Arctic heat pumps - air to water - 48000 BTU only $6k - . 60k BTU $6k 
- CO2 based thus eco - R744 - but just for heating and not cooling - 
- 15000 BTU - 65C max - . $3500 for the heat pump outdoor unit only , $5400 for system . Outdoor unit already has water heat exchanger, so that's all we need. 1700W usage! One 6kW inverter runs 3 of these.
- Rheem Performance Platinum - has heat pump only mode, heat pump is only 4200BTU.  (1.2kW heat pump + 4500 electric element)
- Accelera, $3k, only 1800W heat pump output 
- Ruud - 4200 BTU compressor = $1664. If get 6 of these, that is $10k. 
- 20 gph recovery to 145F - , claims 5x more efficiency than resistance heater.
IBC totes in a crawlspace of SEH 2000 with a 12kW PV system and a $6000 off the shelf heat pump get us to full winter and summer heating/cooling with storage for 20 days if sun doesn't shine. Buffett Jones loved this when I told him this evolution, we should be able to implement this in one of our next 10 builds while coming out at a $100k SEH 2000 materials cost. Zero CO2 because it's PV power. Details at IBC Tote#Calculations, where cost is $9.5k for a 25 tote (5 day) system.
- Heat Pump
- Ground Source Heat Pump / Ground Freezing (I'll get to it later, but it would be interesting to crunch the numbers of this, vs IBC based systems, vs something akin to a pool, or Cistern but for thermal storage, also those Insulated Thermal Working Fluid Tanks i was plotting for the ultimate Solar Hot Water + Hydronic Heating System