What size pool pump do I actually need?

Most residential pools need a smaller pump than you think. For pools up to 20,000 gallons with 1.5-inch plumbing, 1 HP is enough; go to 1.5 HP only if you have 2-inch pipes or significant elevation change. Oversizing wastes energy and causes cavitation. The real solution is a variable speed pump—you dial in the exact flow rate you need and save 50-80% on electricity.