The Pool Pump Affinity Law: Why Slower Saves You 87%

There's a law of physics that explains why variable-speed pool pumps save so much energy. It's called the affinity law, and once you understand it, you'll never look at a single-speed pump the same way again.

The Simple Version

The affinity law says: pump energy use = speed × speed × speed (speed cubed).

That means cutting the speed in half doesn't cut energy use in half. It cuts it by a factor of eight.

Why This Matters for Your Pool

Your pool doesn't need full pump speed most of the time. Filtration, circulation, and skimming all work fine at lower speeds. The only time you need full speed is for:

• Running a pool cleaner that requires high flow
• Heating (some heaters need minimum flow)
• Backwashing a filter
• Shocking or chemical mixing

That's maybe 10-20% of your pump's operating time. The other 80-90% can be done at low speed for pennies.

Real Numbers

At 1,750 RPM — a common overnight circulation speed — the pump uses 87% less electricity than at full speed. And it's still moving 35 gallons per minute, which is plenty for filtration.

The Car Analogy

Think of it like driving. A single-speed pump is like a car that only has one gear: 80 mph. Whether you're cruising through a neighborhood or merging onto the highway, you're going 80 mph. It's loud, inefficient, and wears everything out faster.

A variable-speed pump is like a car with a transmission. It can do 80 mph when you need it (vacuuming, heating), but it can also do 30 mph for everyday driving (filtration, circulation). The fuel savings are enormous.

But Doesn't Slower Mean Less Circulation?

This is the most common question we get. The answer: you run the pump longer at lower speed to move the same total water volume.

A single-speed pump running 8 hours at 3,450 RPM moves about 33,600 gallons. A variable-speed pump running 12 hours at 1,750 RPM moves about 25,200 gallons — but it uses 75% less energy to do it. And for most pools, 25,000 gallons of daily turnover is plenty.

If you need more circulation, you can run 14-16 hours at low speed and still use less energy than 8 hours at full speed.

The Bottom Line

The affinity law isn't marketing hype — it's physics. A variable-speed pump upgrade saves 50-80% on energy costs because it doesn't have to run at full blast all the time. For a typical Arlington pool, that's $500-800 per year in savings.

And with the DOE now requiring variable-speed motors on all new pumps 0.5 HP and above, single-speed pumps are on the way out anyway. The physics was always on the side of variable-speed — now the law is too.

Want to See the Savings for Your Pool?

We offer free pump assessment. We'll measure your current energy use and show you exactly what you'd save with a variable-speed upgrade.

Call 682-399-2593 or get a free quote online.

Project 36 Services — Family-owned pool service in Arlington, TX since 2005. Call 682-399-2593 for a free estimate.