I was told the pool is 21k gallons, but I think it's a bit higher based on measuring. The main body is 16x29, 5.5 ft average depth for 19,140 gallons. I have two half-circle sections on either end that are 12x4. I plugged a 12x8 at 3ft for the shallow end into an oblong calculator, then took half for it to be a half-circle, then half again to account for the steps into the pool, which added 500 gallons. Did the same with a 12x8 at 8 ft for the deep end, halfed only once for the semi circle to add 2,650 gallons, so a total of about 22,290 gallons. So ideally I think I'd aim for about a ~45 GPM flow rate to get a turnover in a ~8.5 hours. I'd also be fine with aiming for ~37-38 GPM and running for 10 hours, as the pumps I've been looking into would still net about $150 in energy savings due to the lower amperage, even with the increased run time.

The pool came with the house so I don't have any designs or anything for the pipes in ground, but I've measured piping on how I think it would be laid out. This is all 1.5" PVC.

- Skimmer 1: 80 linear ft. Assuming 2ft drop, 3 ft raise, 85 total
- Skimmer 2: 40 linear ft. Assuming 2ft drop, 3 ft raise, 45 total. Not sure where these two join, so I'm assuming they join underground closer to the pump.
- Main drain: 45 linear feet, assuming a max of 1ft drop, then max of 10 ft raise. Probably ~55 ft total
- Equipment lines: 12 linear feet. 2ft raise up to sand filter included
- Return line: 70 linear feet, total of about 3-4ft drop to pool

I've counted 10 elbows above ground. 1 is going away for sure, I believe I can remove another 2 placed right outside the filter as well. I speculate there are about 12 underground, so a total of 22 currently. I have one 3-way valve right before the pump, and the tee into the booster line but that will be removed if the booster line is going away. I've counted 18 couplings total, though I should be able to remove at least 8 when replumbing the stuff around the equipment. I'm sure there are more under ground with the length of some of those runs though.

Outside of that, my pump is about 1 ft above the pool surface, and my filter is a Hayward S244T2, and based on the head loss rates in its manual, 45 GPM would add ~13 ft of head loss to the system, or about ~9 ft at 38 GPM. I'm not sure if that includes the Hayward SP0714T multi-port valve on top, which adds in ~7 ft at 45 GPM, or ~5 ft at 38 GPM.

I plugged all that into Pentair's calculator (~275 linear feet, 1.5" diameter, 1 foot lift, 21 elbows. Then either 45 GPM/20 feet misc or 38 GPM/14 feet misc) for about ~66 feet at 45 GPM, or ~48 feet at 38 GPM. Is that roughly accurate? I've ran these numbers through the stuff on InyoPool's guide subbing in Schedule 40 flow rates I've found through either Sta-Rite or Watts Water using my intended lower flow rates instead of the 70 GPM they use in various places, but it ended up higher than the Pentair site. However, I've seen a few places say InyoPools guide gives higher numbers than expected. I've also run them through InTheSwim's guide, again trying to account for the differences in flow rates but get ~79 feet at 45 GPM and ~59 feet at 38 GPM. I'm not sure if the latter are over-estimating in general/the unions are adding up or the Pentair one is under estimating.

As far as pump selection, I've mainly been eyeing the Pentair Whisperflow as a replacement. If the Pentair calculator numbers are accurate, then I figure I can either pick up a 3/4 HP model and run it for ~8.5 hours (66 ft/45 GPM), and it will likely be a bit oversized, though that might be good incase there's anything underground I can't account for. I'm not sure how the 1/2 HP would work, assuming I'm aiming for a lower flow (48 ft/38 GPM), the chart indicates it would run at 55 GPM, which should then... result in increased head loss? Regardless, if the latter, larger numbers I got are more accurate it seems like a 1 HP version would be slightly underpowered at 79 ft/45 GPM, and a 1/2 HP model would be right on the money for 59 ft/38 GPM, but not leave any room for unknowns in the system.

I've read about using a vacuum and pressure gauge into the pump basket and pump volute, respectively, to measure the current TDH of the system, which might give me a better idea of what's going on underground, but I can't see anyway to get both gauges into the pump without separating the pump itself from the basket since the volute drain plug is between the volute and pump basket. Can you run these on a short hose and still get accurate results? Or will it even help if the pump itself is being replaced?

Any advice on better sources or head loss rates or pump models?