Since the pump is down in the well suction head would e determine by the difference between water level and how much further underwater it is. 2.3' per lb. so if the pump in 23 feet under = 10 lbs. If you would time a 5 gallon bucket on the return side close at the well head it should get you close. It use to be when using city water 2 gpm per ton.
The unit what are the in and out water temps, supply return temps.