Replacing or installing a submersible well pump is one of the more significant investments a homeowner can make in their water system. Buy the wrong one and you're either sending it back or dealing with a pump that doesn't perform. This guide walks you through exactly what to look for so you get it right the first time.
Step 1: Measure Your Well Depth
The first thing you need to know is how deep your well is. This determines how much "head" your pump needs to overcome — essentially how hard it has to work to push water to the surface. Your well driller's report will have this information, or you can measure it yourself by lowering a weighted string into the well until it hits the bottom.
Most residential wells in the US are between 100 and 400 feet deep. If your well is shallower than 25 feet, you may not need a submersible pump at all — a shallow well jet pump like the Franklin Electric VersaJet Pro would be a simpler and less expensive solution.
Step 2: Know Your Well Casing Size
Well casings come in two common residential sizes: 4-inch and 6-inch. Your pump has to physically fit inside the casing, so this matters.
- 6-inch casing — the most common in modern residential wells. Most Franklin Electric FS Series pumps are designed for 4-inch and larger casings.
- 4-inch casing — older or smaller diameter wells. The Grundfos SQ and SQE series are specifically built to fit 3-inch or larger casings where a standard 4-inch pump won't go or could get rusted into place with such a tight tolerance.
If you don't know your casing size, check your original well driller's report or measure the inside diameter of the casing at the top.
Step 3: Figure Out Your Flow Rate Needs
Flow rate is measured in gallons per minute (GPM). For most single-family homes, a 10 GPM pump is more than adequate. As a rough guide:
- 1-2 people: 6 GPM minimum
- 3-4 people: 8-10 GPM
- 5+ people or irrigation needs: 12 GPM or more
All of our Franklin Electric FS Series and Grundfos SQ Series pumps are rated for 10 GPM, which covers the vast majority of residential households.
Step 4: Choose the Right Horsepower
Higher HP means more ability to push water against head pressure — meaning it's more about your well depth than your household size. General guidelines:
- 1/2 HP — wells up to around 150 feet deep
- 3/4 HP — wells between 150 and 250 feet deep
- 1 HP — wells over 250 feet deep
These are general guidelines. If you're close to the boundary, it's usually worth stepping up to the next HP rating for peace of mind.
Step 5: Match Your Voltage
Most residential submersible pumps run on either 115V or 230V single-phase power. Check your existing wiring or breaker panel to confirm what you have before ordering. Running the wrong voltage will damage your pump motor immediately.
- 115V — common in older installations and smaller HP motors
- 230V — the standard for most modern residential well installations
- 2-wire vs 3-wire — 2-wire pumps have built-in starting components and don't need a separate control box. 3-wire pumps require a matching control box.
Step 6: Don't Forget the Control Box (for 3-Wire Pumps)
If you're buying a 3-wire submersible pump, you need a matching control box. The control box must match your pump's exact HP and voltage — a mismatched control box will damage your motor. Franklin Electric control boxes are the OEM-recommended choice for Franklin Electric pumps.
If you're buying a Grundfos SQ Series pump, no control box is needed — the starting components are built into the motor. However the SQE Series requires a Grundfos Controller.
Still Not Sure? Call Us.
Choosing the right pump doesn't have to be complicated. If you know your well depth, casing size, and voltage, we can point you to exactly the right pump. Call us at 715-281-5885 and we'll help you figure it out.