Briefly, last year we took ownership of a new "old" pool with our home purchase. The owner at the time did not have an eyeball on the closest jet to the pump, and the two times I heated the pool last fall i noted that the water from this "open" return was nice and warm if not a little hot. This year I heated the pool for the first time last night. The pool was covered with the solar, starting water temp was 57, air was 48. I started heating at 11pm. At 6am the water was only 62, but by 11am it climbed to 66, so the heater did its job of the 1degree per hour rule even fighting an uphill battle.
So the open jet from last year, I did put a 3/4 inch eyeball there. It is my most powerful jet and also the only original (still with the old black pipe) I think this may leak under the concrete deck and perhaps the owner did not use an eyeball to reduce the pressure. Anyways feeling the water with the heat on, it did not seem as "warm" as it did last year. So I removed a different eyeball and viola - the water felt really warm. So is this a perception thing where the force from an eyeball just blows the heated water by so fast drawing in the cold surrounding water where you can't tell by hand and removing the eyeball slowed it down where you "can feel it" or in my case would there be a benefit to slowing down the water and thereby allowing more time spent in the heater core even if milliseconds?
New to all of this so thanks in advance, and BTW thanks to TFP so far I have sparkling water after reading here all winter.