For the most part the heat pump is left on because it takes quite a while for the heatpump to bring up the water temp most are less than 100,000 BTU/hr as opposed to gas heater 400,000 BTU/hr. You can make the system more efficient by having the heatpump run during the warm part of the day like 11:00 am to 7:00 PM. I do this by having my main pump on a timer for those times plus an hour before and after so I have 10 hours filtering time. The heatpump won't run unless there is flow in the pipes so this works pretty well. A cover really helps with nightime losses.