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Why slower wins: the cube law
pump power ∝ speed³ → half speed = ⅛ power for ½ the flow same water moved, ~¼ the energy
It feels like cheating, but it's just physics: fluid friction punishes speed brutally, so moving the same daily gallons gently costs a fraction of moving them fast. Single-speed pumps can't exploit this; variable speed pumps are built around it.
A worked example
A 1,700W single-speed running 8 hours costs about $2.31/day. A VS at 350W for 16 hours — moving comparable water — costs $0.95. Over a 6-month season that's ~$250 saved per year, paying back a $1,100 install in ~4.4 years, or ~3 with a typical rebate. Hotter climates with longer seasons pay back nearly twice as fast.
Sizing the low speed
Use the pump size calculator for your turnover GPM, then find the RPM that delivers it — most pools land shockingly low. The winning schedule: low RPM most of the day for filtration and skimming, a short high-RPM burst for the heater or vacuum, and the run time calculator to price whatever schedule you pick.
Frequently asked questions
How much does a variable speed pump save?
Commonly 50–80% of pump electricity. Power scales with the cube of speed: half the RPM moves half the water for one-eighth the power, so running longer at low speed filters the same volume dramatically cheaper. On a $70/month single-speed habit, that's $400+ per season.
Are there rebates for variable speed pumps?
Frequently — many utilities pay $100–500 for the upgrade because it genuinely reduces grid load. Search '[your utility] pool pump rebate' before buying; several states have also phased out new single-speed pumps entirely.
What speed should I run a variable speed pump?
As low as still skims properly for daily filtration (often 1,200–1,800 RPM), higher briefly for vacuuming, heating, or spa jets. The low-speed hours are where the cube law pays you.
How long do variable speed pumps last?
10+ years is common — the permanent-magnet motors run cooler and gentler than induction single-speeds. Between lifespan, rebates, and the cube law, it's the rare upgrade that's genuinely just better.