When I bought our new house I didn't like any of the equipment, much of it was on the last leg, and so many plumbing leaks I simply poured a new pad and started 100% new, as well as a little further from the pool so noise and sight hidden just around the corner of the house. I went with all 2" PVC based on reading input here, as well as in the past having a reef tank where every bit of flow saved was a plus.
However, in regards to a pool I'm questioning the usefulness at least with my current configuration. Everything was 1 1/2" when I moved in, so everything below ground still is. Main drain dedicated line, two skimmers that tie together to a single line somewhere, two returns tied together, and one dedicated pressure return. Depending on which one they run probably 30-40 feet. At the pad everything goes to 2", the main and skimmers converted to 2" before the Tee tieing them together.
However, the sand filter has 1 1/2 inch fittings so it has to get necked down and then back up there. I'm now starting to prepare to plumb in a new heat pump and it also has 1 1/2" fittings so it will need to be necked down again. So, with everything underground at 1 1/2 and now two places even on the pad where it has to be reduced to 1 1/2" am I really saving that much trying to stick to 2" where I can other than a little more expense for fittings and making the work of plumbing a little more difficult? I understand there is less friction loss, but with it being such a small fraction of the total plumbing I'm wondering if the difference would really be measurable by anything other than a gauge or just a formula showing there's a minor difference.
If the pool itself already had 2" I'd likely worry more and even make more effort to avoid equipment that's not 2". I also have about 60 feet of 1 1/2" PVC and a box full of fittings in the garage and only 10 feet of 2", so before I run to Lowes I'm basically looking for opinions on if I should continue bothering with 2" for a small fraction of total plumbing. I won't be intentionally changing anything BACK to 1 1/2 that's now at 2", but just returning to using 1 1/2" when adding or making changes anyway. A whole lot easier for me anyway to cut right through 1 1/2 compared to 2" that barely fits into my PVC cutter Agree, or disagree that just friction loss difference probably isn't that big when most of the distance is already 1 1/2 anyway?