I'm using 50' x 3/8" with a chugger pump throttled back about 10-20% and I have excellent flow. I have a buddy that has 40' x 1/2" running a march 809 that needs to be restricted well over 50% to slow down his flow to achieve sufficient heat transfer. I also pump into the top of the coil, not sure if he does.
What are you guys using to dial these back? Valve's or maybe a dimmer switch?