Back in 1999, my circulator was replaced along with the furnace. The old unit was a Taco model where the motor rested in a C-Frame with a spring-loaded couple to the impeller shaft, the whole thing was about 1.5 feet long. I now have a Taco 007, 0-20GPM and head-range=0-11ft. What's the difference between the old model, and this newer model? What are the symptoms of a pump that's under-specd? Over-specd? Is 'head-range' the number of feet the pump must be able to lift the water given the piping structure of the house? No DIY, just wondering if this affects efficiency at all...