Choosing a variable speed pump shouldn’t feel like a guessing game. We walk through a simple, field-tested way to size the right unit by matching your current single-speed horsepower to modern total horsepower (THP), accounting for plumbing size, distance, and voltage, and then using RPM control to hit your flow goals without wasting energy. No fluff—just practical rules you can apply the moment you step onto the equipment pad.

We start by translating old-school horsepower labels into today’s THP ratings and explain why you can safely choose equal or slightly higher THP and run it slower for quiet, efficient filtration. You’ll hear how pipe diameter, elbow count, elevation, and equipment distance shape total dynamic head, and why most backyard pools don’t need elaborate TDH calculations. We compare VS and VSF pumps, demystify how auto-flow control can handle minor resistance changes, and outline clear ranges: what to buy if you’re replacing a 1 HP, 1.5 HP, or 2 HP single-speed. We also unpack voltage realities on older 120 V systems so you don’t overbuy a pump that can’t deliver its full potential.
We break down how to size a variable speed pump by matching total horsepower to your existing single-speed, factoring in plumbing, distance, and voltage, and ignoring noise metrics that don’t move the bill. Clear steps, practical ranges, and brand tips help you buy once and set it right.

• matching single-speed HP to VS total horsepower
• when TDH matters and when it does not
• pipe size, distance, elevation as key resistance factors
• voltage limits on older 120 V systems
• VS vs VSF and why auto flow can help
• practical THP ranges for 1, 1.5, and 2 HP replacements
• why WEF differences are marginal for cost
• using a flow meter to set RPM and GPM
• brand consistency for easier install and automation

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