variable speed pump

I think some of the newer style Electronically Commutated Pumps are Variable Speed drive just not sure if you can externally control their speed as they usually run to standard internal programs. Pretty rare to see a VFD that will drive a single phase pump. Many are single phase input but they output three phase.

Been there with control resources nimbus and stratus, they claim will work with a regular taco pump, it does on the bench rotate at 1 volt, however under a hydronic install you won’t see rotation until the output is 20 pct., making for a nonlinear response. This is fine if your using the midrange of the output but under 30 pct output it will want to oscillate to try to make setpoint. You can get a variable voltage pump from taco but it’s really just a onboard stratus. If ballpark is good then you are all set but I’m not sure how a much better a ecm pump would react? For finite control I’d recommend a 3 way valve, and proportional actuator like a belimo characterized control valve with a proportional actuator 2/10vdc or 4/20ma, that can be controlled with a pid controller. If you want simpler, same valve with a floating point actuator, tekmar makes a controller.

The only vfd I use is for controlling the speed of my 3 ph 1hp draft inducer for my boiler, the motor is a 56c frame, I’d guess 25 lbs. I wouldn’t think it would be compatible to convert efficiently into a circ.
Most circs are 1/4 to 1/25 hp for residential use, you could try mouser electronics or automation direct for a small motor.
Why not just put the stratus to a taco circ and see if it’s good for you, there’s no telling if a different motor is going to be any better, and the how are you interfacing the motor to a volute. You might also find the wink link to be the stratus.

tekmar makes a variable speed controller for circulators and works with the standard taco line (but not the new ecm pumps).

I control combustion( primary, secondary air and the draft inducer ) with a eurotherm mini8 controller. I also use it to control a tank mix pump and start the draft inducer and stop it at the end of a burn.
On the hydronic side I use a eurotherm single loop pid controller for the belimo mix valve for the reset mix temp to the house. Tekmar supplies outdoor reset calc, staging for backup boiler and all zoning.