I will reiterate what is in my signature.
17K gallon 18X36 inground pool.
75K BTU natural gas heater.
1 HP pump.
My question is what can be expected for a temperature rise of my pool? It seems like it takes forever to heat my pool. I do not know what is normal. I did an experiment where I measured the pool temperature. Then I measured the temperature of the water from the return jets. There is a 2 degree rise.
What concerns me is that my heater is 30 years old (yes, 30 years old!) and perhaps the exchanger is plugged or not working properly. I replaced the burner tray 5 years ago. The flames from the burners are nice and blue. The heater when on consumes 55 cubic feet of gas per hour.
Perhaps the real problem is that the heater is undersized?