When I build my next house, I will use active solar, I got the panels & BIG 1,000gal tank cheap off craigs list.
I got a new Vie$$man dual coil 79gal indirect DHW SS tank off Ebay, $1000
My small Burnham RV3 boiler / solar system will add heat to tank via the bottom coil.
If solar tank is hot enough it will provide heat to Vie$$man tank.
The 79gal water contained in the tank will provide DHW (with TMV tempering it down to 134*F) with recirculation to fixtures.
The top coil will provide low temperature ODR controlled heat to the pex in concrete floors, continuous circulation with 3-way zone valves.
An Erie Boiler Boss 3000 Outdoor Reset Controller (another Ebay steal $160) will control the speed of a Taco 007
ECM pump can't be used here as Erie BB3000 unit uses PWM to control the variable speed of standard PSC motor pumps:
Note:
permanent-split capacitor (or PSC) motor also known as a capacitor-run motor, Power Factor typically from around 0.85 or 0.90 at full load to as low as 0.12 at no-load