"Right-sizing" a system after renewable additions

2manyprojects

I recently added renewable fuel options (wood, pellets) to a fairly large thirteen year-old home that has previously relied on a single boiler for heat and DHW.  Now my boiler is oversized and I'm looking for more efficient options.  In addition, I plan on adding solar hot water to the mix in the future and need something that will integrate well.

  **The home**: 1200 sq.ft./floor (Basement, 1st, 2nd); 3600 sq.ft. heated space.  Attached 1000 sq.ft. mother-in-law appartment on the other side of the garage. 

  **The system**: Radiant floor heating throughout.  Shared DHW with a 230' round-trip insulated recirculation loop to the appartment controlled by an aquastat set to 5-degree differential.  Fuel: Propane.  Boiler: Buderus G234X-45 paired with a Phase III HL-60 indirect water heater.  Both the water heater and radiant supply are fed directly from the main boiler loop.

  **The situation**: The house is 5-star energy rated and we found that the wood & pellet heating options eliminate the need for radiant heat (warm floors aside).  This means the Buderus G234X-45 is waaaaaay oversized for the DHW needs and is running inefficiently.  I tracked the on-off cycles for the recirc loop and boiler.  Results: Recirc cycles apprx every 1/2 hour.  At 3.5gal/cycle I calc'd a 300BTU/hr. energy loss.  Boiler cycles apprx every 1.5 hours and runs about 4-5 min. each time.  Including showers, dishes, etc. that makes about 1.5-2.0hrs run time per day.  I have all lines including the boiler loop insulated but sure I'm losing a bunch of heat from the boiler.

  **Questions**: Some questions I see are these: 1) Should I get a separate DHW source for the apartment and eliminate the recirculation loop?, 2) Should I continue to use the Phase III tank?, and 3) What are the best options for  DHW supply for the main house and/or apartment that will integrate well with solar in the future?

I have considered options ranging from on-demand units for each side to just replacing the boiler with a high-efficiency low-mass unit.  I'm not a pro but trying to do my homework.  All opinions welcome.  Thanks.