S320PT-20 S Series Direct Drive Pump, 20’

Choosing the correct pool pump depends on pool size, plumbing size, and system features (heater, spa, water features, etc.). Bigger is not always better – an oversized pump wastes energy and can damage equipment.

Determine Your Pool Size

Rectangular Pool
Length × Width × Average Depth × 7.5 = Gallons

Round Pool
Diameter × Diameter × Average Depth × 5.9 = Gallons

Recommended Pump Size by Pool Volume

⚠️ Note: Modern variable-speed pumps often replace larger single-speed pumps at lower HP ratings due to higher efficiency.

Plumbing Size Matters (Very Important)

Oversizing a pump on small plumbing can cause:

• Excessive noise
• Poor filtration
• Heater & filter damage

Pump Type Comparison

Single-Speed Pumps

• Lower upfront cost
• Higher electricity usage
• Becoming obsolete in many states

Best for: Basic systems, budget replacements

Dual-Speed Pumps

• High & low speed operation
• Lower energy cost than single-speed

Best for: Simple upgrades where VS is not required

Variable-Speed Pumps (Recommended)

• Most energy efficient
• Quiet operation
• Programmable speeds
• Often utility rebate eligible

Best for: Nearly all residential pools

???? A 1.65–2.7 THP variable-speed pump can replace most 1 1/2 – 3 HP single-speed pumps.

Systems That Require a Larger Pump

You may need a larger pump if your pool has:

• Spa spillover
• Waterfalls or deck jets
• Solar heating
• In-floor cleaning system
• Long plumbing runs

Common Sizing Mistakes

❌ Choosing HP only (ignore flow & plumbing)
❌ Oversizing “just to be safe”
❌ Ignoring filter and heater flow limits

✅ Always size for flow rate (GPM), not just horsepower.

Still Not Sure?

If you’re replacing an existing pump, check the motor label for:

• HP
• THP (Total Horsepower)
• Voltage
• Plumbing size

If you’re unsure, contact us and we’ll help you choose the correct pump.