“What horsepower do I need?” is the question almost everyone asks, and it is the wrong place to start. Two 1 HP pumps from the same manufacturer can be built for completely different jobs — one for high flow at shallow depth, one for low flow from deep down. Put the wrong one in your well and it will struggle for its entire, shortened life.
This is how sizing actually works, in plain terms, so you can check whatever you are quoted.
Step 1: How much water the house needs
Pumps are rated in gallons per minute (GPM). The house needs enough flow to cover what is realistically running at the same time during the busiest part of the day.
A common rule of thumb is roughly one gallon per minute for each water-using fixture in the house — each sink, toilet, shower, tub, the washing machine, the dishwasher, each outdoor spigot. Many family homes land somewhere between 8 and 12 GPM.
| Add flow for | Lawn irrigation, livestock, a pool, a guest house, a large household with overlapping morning routines. |
| Do not add flow for | Occasional peaks that a properly sized pressure tank covers. Storage handles short bursts; the pump handles sustained demand. |
Step 2: How hard the pump has to push (total head)
Total dynamic head is everything the pump is working against, expressed in feet. It has three parts.
Lift
The vertical distance from the pumping water level — where the water sits in the well while the pump is running, which is lower than where it sits at rest — up to the pressure tank. If the house sits uphill from the well, that elevation counts too.
Pressure
The pressure the switch asks for, converted to feet. One psi equals about 2.31 feet of head. A 60 psi cut-out adds roughly 139 feet on its own — more than many people’s entire well depth.
Friction
Resistance from pipe, fittings and the run between the well and the house. Longer runs and narrower pipe add more. On a long rural driveway it can be significant.
A worked example. Pumping level 150 feet down. Tank 10 feet above the wellhead. Switch at 40/60. Moderate pipe run.
Lift 160 ft + pressure 139 ft + friction ~20 ft = around 320 feet of total head at 10 GPM. That pair of numbers — 10 GPM at 320 feet — is what gets matched against manufacturers’ pump curves. The horsepower falls out of that match.
Step 3: Match it on the pump curve
Every pump has a performance curve: at this many feet of head, it delivers this many gallons per minute. As head rises, flow falls, until at some height the pump delivers nothing at all.
The right pump is one whose curve passes through your required flow at your total head, with that point sitting in the efficient middle of the curve rather than at either end. A pump operating at the edge of its curve runs hot, wears faster, or both.
Step 4: Check it against the well
This is the step that is most often skipped, and the one that matters most in the Upstate.
Every well has a yield — how fast water flows back into it. Many Upstate wells are drilled into fractured rock, and yields vary enormously from one property to the next. If the pump draws water faster than the well refills, the water level drops until the pump sucks air.
That makes it worth knowing your well’s yield before choosing a pump. After the extended dry spell across South Carolina through 2025 and 2026, some wells are producing less than they did when they were drilled. A yield and flow test tells you what you actually have to work with.
If the house needs more than the well can produce, the answer is storage — a larger pressure tank or a holding tank with a booster pump — not a bigger pump.
Jet pump or submersible?
| Shallow well jet pump | Water within about 25 feet of the surface. Physics limits how far suction can lift. |
| Deep well jet pump | Workable to roughly 90 to 100 feet in the right conditions, with falling efficiency as depth increases. |
| Submersible | The standard answer for drilled wells beyond that range, which covers most drilled wells in our area. |
The differences are explained fully in jet pump vs submersible.
Why bigger is not better
- It can out-pump the well. Low-yield wells run dry under an oversized pump.
- It short cycles more. Higher flow empties the tank’s drawdown faster, so the pump starts more often unless the tank is resized too. See pressure tank sizing.
- It can run off its curve. A pump built for far more flow than the system needs ends up operating inefficiently.
- It costs more to buy and to run. Larger motor, larger wiring, larger generator if you ever need one — see generator sizing for a well pump.
Just as common is the opposite problem: a pump undersized from the day it went in, or one that was right until the family added an irrigation system and a second bathroom. That pump runs long, never quite reaches pressure, and wears out early.
Where we work
Pump sizing and installation across Upstate South Carolina
| ✓Anderson | ✓Greer |
| ✓Taylors | ✓Mauldin |
| ✓Simpsonville | ✓Fountain Inn |
| ✓Travelers Rest | ✓Easley |
What to remember
| 1 | Start with GPM and head. Horsepower is the answer, not the question. |
| 2 | Pressure counts as height. Every psi at the switch is 2.31 feet the pump must push. |
| 3 | Use the pumping level. Not the resting level, and not the well depth. |
| 4 | Never out-pump the well. Short on water means more storage, not a bigger pump. |
| 5 | Size the tank with the pump. The two are one decision. |
Frequently asked questions
What size well pump do I need for my house?
One that delivers the flow the house needs at peak, often 8 to 12 gallons per minute for a family home, against the total head of your system, and never more than the well can yield. Horsepower follows from matching those numbers to a manufacturer’s pump curve.
How many GPM does a house need from a well?
A common rule of thumb is about one gallon per minute per water-using fixture. Many homes need 8 to 12 GPM, with more for irrigation, livestock or large households.
Is a 1 HP well pump enough?
It depends entirely on the flow and head required. A 1 HP pump suits many typical Upstate homes, but the same horsepower is built in different versions for high flow at shallow depth and lower flow from deep wells. The pump curve, not the horsepower, decides.
Can a well pump be too big?
Yes. An oversized pump can draw a low-yield well down until it runs dry, short cycles more often on a tank that was not resized, and runs inefficiently.
How does well depth affect pump size?
What matters is the pumping water level, not the drilled depth. The deeper the water sits while the pump is running, the more head the pump must overcome and the more capable it must be.
What is total dynamic head?
The total resistance the pump works against, in feet: the vertical lift from the pumping water level to the tank, the system pressure converted to feet at about 2.31 feet per psi, and friction losses in the pipe.
My well cannot keep up with the house. Should I get a bigger pump?
No. If the well cannot supply water fast enough, a bigger pump empties it faster. More storage, such as a larger pressure tank or a holding tank with a booster pump, is usually the answer.
Replacing a pump?
Size it to your well, not to the van
We measure the water level, check the yield, work out the head and match the pump and tank to your household — then give you a fixed price in writing before any work starts.
Open 7am–9pm, seven days · No call-out fee with a repair · Fixed price agreed in writing
See our submersible pump and jet pump pages, or read what a replacement quote should include.
