Dale in my system the thermostat's only control the the zone valves the circulator runs continuous , I have a by pass loop at the circulator to pervent cavitation if all four zones are closed. Pictured the by pass loop, the flow control is at the top left side.The dead end at the bottom of the loop is for drying gloves !
I haven't done any electrical measurements yet, but I'm hoping that my two Taco delta T circs will save money over time. One, on the pellet boiler is controlled by an aquastat surface mounted on the pellet boiler's output and set to close at 140 degrees, never stops running, although its rpm is very low when the return line is near or at 140 and when the output is near 140. The greater the deltal T between the two, the faster the pump runs. If constant running is good, then slow and constant have to also be good, or better.
The 007 was about $173 and the 0012, $380. I really think that the standard or 3 speed pumps might be a much better buy because, although I haven't calculated energy savings, I don't think these pumps would use the difference in price between the Delta Ts and regular pumps over their lifetime. I wanted the potential savings, but I also wanted the least noise, especially after listening to a big ol' centrifugal blower from my hot air wood furnace rumble on a set a worn bearings. Now the house is too quiet and I can still hear a 3 speed Grundfos kick on when any thermostat calls for heat. Can't complain though because compared to before, it's very quiet in here.
