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I'm completely new to pools and planning on building an in-ground pool. Of the different bids I have so far, one builder says he uses 2" PVC for the main drain, and another emphasizes that he uses 3" for the main drain and this is much better. This is for a 28,000 gallon pool. Is this difference significant? Does the power of the pump play into this?
Thanks for any help.
For all plumbing, larger pipe will usually help increase the efficiency of the pump but only up to a point. Using 2.5" pipe for all pool plumbing is a good idea including using separate runs for the suction side so that the main drain and each skimmer has it's own line from pool to the equipment pad. You can get away with smaller pipe but the up grade usually doesn't cost that much more and will probably save you energy costs in the long run.
There's a significant difference in the maximum flow rates vs pressure in those pipe sizes. There are some charts here if you're curious but as mas985 said; larger pipe will be better (to a point). Personally I'd go with the 3". The power of the pump will play a role, but it won't change the general rule that 3" trumps 2". It could be that the first builder is using a smaller pump than the second, or just as simple as the difference isn't a huge deal. On the other hand, he could just be less knowledgeable than the second builder.
If you read the information provided here, you'll see that to figure it all out precisely will take a lot of work and a calculator... on the other hand, I'm guessing a pro pool guy probably has some more general rules they follow to make life easier.
http://flexpvc.com/WaterFlowBasedOnPipeSize.shtml