How to Size and Choose the Right 1 HP Submersible Pump for Your Well? | GPM, Not Horsepower

Sizing a 1 HP well pump starts with required GPM at total dynamic head — horsepower alone tells you almost nothing about flow or pressure.

Two wells of the same depth can need completely different pumps, and the number printed on the box won’t tell you which one fits yours. Horsepower describes the motor; flow and lift come from the impeller and the stages stacked above that motor.

A 1 HP submersible well pump can be built to push 5 gallons per minute to 609 feet of shutoff head, or 35 GPM to 161 feet. Same motor, opposite jobs. Sizing comes down to a short set of numbers, and the mistakes are expensive: an oversized pump short-cycles, an undersized one starves the shower.

How Do You Size A Submersible Pump For A Well?

Sizing starts with the flow and head your household needs, never with horsepower. Work through six numbers in order and the model names itself.

1. Add up demand in GPM. Count fixtures, irrigation, livestock, and anything that might run at the same time — not the pump’s nominal rating.
2. Measure two water levels. Record the static level and the pumping level, then use the pumping level for vertical lift. Static readings understate the work the pump does.
3. Turn pressure into feet. One psi equals 2.31 feet of water, so a 40 psi target adds about 92 feet of head on top of the lift.
4. Add up losses. Drop pipe, horizontal runs, fittings, check valves, filters, treatment gear, and any backflow device all cost performance. Lift plus pressure head plus friction equals total dynamic head, or TDH.
5. Read the pump curve. Pick the model whose published curve delivers your GPM at your TDH, near its efficient range. Shutoff head is a ceiling, not a setting.
6. Check the well itself. Confirm the casing fits the pump, the intake stays submerged at the lowest pumping level, and the well recovers fast enough to feed that flow continuously.

Well recovery is where most systems fail. A pump that outruns the well’s recharge rate drags the water level down to the intake, and a pump that runs dry can be ruined in minutes.

What A 1 HP Submersible Well Pump Actually Delivers

Current Franklin Water 1 HP models span roughly 5 to 35 GPM and 161 to 618 feet of shutoff head, so horsepower alone rules almost nothing out.

Two 1 HP pumps can be near-twins in one well and useless in the next. A 10 GPM model with 11 stages builds far more pressure than a 35 GPM model with 5 stages, which trades head for volume. Match the curve to your calculated TDH, not the label.

Flow, stage count, voltage, and shutoff head are listed separately for every configuration in Franklin Water’s FS Series performance data, so order by model number rather than by description.

Casing, Wiring, And Well-Yield Limits

All of these pumps are 60 Hz, 230 VAC single-phase units built for 4-inch or larger clean-water casing, so the electrical details decide whether your existing control equipment works with a new pump.

Three-wire models need a compatible control box; Franklin lists part 2801084915 for the 20 GPM Series V and the 10 GPM J-Class Tri-Seal. Never swap a 230 V motor for a 115 V one, or a three-wire unit for a two-wire unit, without matching the control box, cable, and overload protection to the new configuration. Every model cited here carries ANSI/NSF Standard 61 approval for drinking water, tops out at 120°F water temperature, and is warranted for 12 months after installation or 24 months after manufacture.

• Casing: a 3.9-inch body with a cable guard needs the full 4-inch bore, so a narrower well rules these pumps out and points you toward a smaller-diameter model.
• Wiring: a 230 V three-wire motor won’t run on 115 V or on two-wire control equipment.
• Prices: Franklin’s product pages don’t publish reliable retail prices, so ask a US dealer for a quote on the exact model number instead of trusting a guess.

The order that works: settle simultaneous GPM demand first, read the pumping level second, convert pressure to head third, total friction losses fourth, and open a curve last. If the model you land on is hard to find, weighing a tested 1 HP submersible pump roundup against those numbers beats reading curves cold.