The Taco Delta-T pump on the tank side of HX would work.
This should work well for recirculation to get almost instant hot water at fixtures.
There will be a small 10W El-Sid 24vdc pump at each of the 3 bathrooms & at kitchen island sink with temp. controlled pumping back to HX via a 3rd return line. The hot water out to fixtures & return line will be well insulated.
The well water input into the HX load side has been preheated in solar storage tank.
http://www.taco-hvac.com/uploads/Fil...ry/102-143.pdf
Pump requires a Run signal OR I could jumper this so it's always on at lowest power (8W).
Pump dip sw controls: #5=off, #4=on, #3=on, #2=off, #1=on
Sensors:
S2 (source) would be on pipe between top of tank & HX.
S1 (load) would be on pipe between bottom of tank & HX.
5*F is the minimum switch selected Delta-T.
Pump slows to it's minimum speed (8W) if S1 is hotter than S2 - Delta-T)
When load (shower etc.) is drawing hot water S1 will drop in temp. relative to S2 & pump will speed up trying to maintain 5*F Delta-T.
This setup will cause a constant circulation in tank, which has good and bad effects.
Good = tank is almost completely up to the temp. set by aquastat, on a long draw the 40 gal. tank will provide as much hot water as say a 60 gal. stratified tank.
Bad = heating tank with DSH & HP will not draw cool water from bottom, which decreases Eff. & thus will take longer run times, I think.