Repiping to 2 inch vs sticking with 1.5 inch on the pad

Started by plumberdave · · 4 replies
Back to the forum
Reply
#1
Look, my pad is original 1.5 inch schedule 40 from when the pool went in and it's held up fine, no cracks, no weeping unions. But I'm swapping the pump this year and keep going back and forth on whether to bump the whole suction and return side up to 2 inch while everything's apart anyway. Less friction loss, pump doesn't have to work as hard, but it's more cutting, more fittings, more time standing in the hole next to the pad. Vinyl 18x36 here, nothing huge. Had a guy a few towns over tell me 1.5 is plenty for a pool my size and 2 inch is overkill unless you're running a bigger pump or a heater that wants more flow. Anybody actually done this swap on a similar size pool and notice a real difference, or is it just more work for bragging rights. Dave

4 Replies

#2
Funny timing, I'm on 2 inch suction with a 22k gallon gunite and even at 60 gpm I'm only seeing something like 1.5 ft of head per 100 ft on that leg, 1.5 inch at the same flow is closer to 5-6 ft per 100 ft just from the Pentair friction tables. For your 18x36 vinyl though your actual run gpm matters way more than mine does, mine's higher just because of turnover math, so not really apples to apples on whether the upsize is worth the hole-standing time.
#3
Never repiped mine but my 15k runs 1.5 inch the whole way and pump doesn't struggle, cartridge filter pressure stays normal even in August heat. If your pool size and pump gpm don't call for it, that's more cutting and gluing for numbers you won't feel on a pool this small.
#4
Ray's right that for a pool his size the pump isn't going to struggle either way, but the piece that's missing is what pump he's putting in. If Dave's going single speed at a fixed high gpm then yeah, 1.5 inch friction loss is basically baked in and he'll never notice it. If he's going VS and actually running a slow turnover speed most of the day, the affinity laws work in his favor regardless of pipe size, head loss drops with flow cubed, so at say 30 gpm instead of 60 the 1.5 inch penalty is already way smaller than people assume from the full-flow friction tables.

So the real question isn't pool size, it's whether he's ever going to add a heater down the line or run higher flow for some reason. If it's staying a vinyl 18x36 with a small to mid VS pump forever, I'd save myself the hole-standing time and leave the 1.5 inch alone, the watts you're chasing by upsizing pipe on a pool that small are pennies a month, not the kind of math that pays back the extra fittings and cutting.
#5
Marcus has it right on the affinity laws, that's the part people skip over. I'd only tell Dave to upsize if a gas heater is anywhere in his future plans, because that's where 1.5 inch bites you, a Raypak or similar wants decent flow through the exchanger and you don't want to be fighting pressure drop on both the heater and the pipe. On my own pad I'm running 2 inch mainly because I've got both a gas heater and a heat pump in series, different story than a straight VS pump setup on a pool his size. For 18x36 vinyl with no heater on the radar, save the digging.