Last updated: September 18, 2026
Choosing the right well pump takes more than matching horsepower to well depth. The pump has to handle your household’s water demand, the distance water must travel, the pressure your system needs, and the amount of water the well can reliably supply.
That is why two Connecticut homes with wells of similar depth can still need different pumps. Differences in pumping water level, pipe friction, household use, and well yield can all change the sizing. If your well records or current pump details are missing, a well pump evaluation can help gather the information needed before you choose replacement equipment.
What HP Well Pump Do I Need for My Home?
For most homes, the better question is not simply “How much horsepower?” You first need to know the required flow in gallons per minute and the Total Dynamic Head the pump will work against. Once those numbers are known, the manufacturer’s pump curve shows which pump and motor combination can handle the job.
Horsepower describes motor power. It does not tell you, by itself, how much water a pump will deliver. Franklin Water, for example, sells residential submersible pumps in several flow ranges and horsepower ratings. Within one product line, 3/4 HP models are available in different GPM configurations with different head capabilities.
That is why a simple chart such as “1/2 HP for shallow wells, 1 HP for deep wells” can send a homeowner in the wrong direction.
| What to check | Why it matters |
| Required GPM | Shows how much water the house needs during higher-use periods |
| Pumping water level | Helps determine how far water must be lifted while the pump runs |
| Pressure requirement | Adds head the pump must overcome |
| Friction loss | Accounts for resistance in pipe, fittings, valves, and filters |
| Well yield | Limits how much water can be pumped sustainably |
| Pump curve | Shows the actual flow a specific pump can deliver at a given head |
| Horsepower | Identifies the motor power paired with that pump design |
The correct pump is the one that can meet the home’s flow requirement at the calculated head without asking the well to produce water faster than it can recover.
Well Depth Is Not the Same as Pumping Lift
A 400- or 500-foot well does not automatically mean the pump is lifting water 400 or 500 feet. Total well depth describes how far the well was drilled. Pump sizing is more closely tied to the water level while the pump is operating, along with the pressure and friction the system adds.
Imagine a 500-foot well with the pump set at 450 feet. If the pumping water level settles at 160 feet below the pressure tank, that 160-foot level is much more useful for estimating pumping lift than the full drilled depth.
Static Water Level and Pumping Water Level
Static water level is measured when the well is resting. Once the pump begins pulling water, the level may drop until inflow from the aquifer catches up with the pumping rate. That lower level is the pumping water level. The difference between the two is called drawdown. Franklin Water uses the pumping water level, pressure converted to feet of head, and pipe friction when calculating Total Dynamic Head for pump performance testing.
The distinction matters most in wells where the water level drops substantially during pumping. Sizing from static level alone can understate the lift the pump sees under actual use.
Where the Pump Sits Is Another Number
Pump setting depth tells you where a submersible pump is installed. It matters for submergence, drop pipe, cable length, and the physical setup inside the well, but the setting depth is not automatically the same as pumping lift.
This is one reason the answer to “How deep can a certain HP pump go?” depends on more than the motor label. Pump design, required GPM, water level, pressure, and other system losses still have to be considered.
Start With GPM and Total Dynamic Head
Pump selection becomes much clearer once you know two numbers: the flow rate the home needs and the Total Dynamic Head, or TDH. In a residential well system, TDH accounts for the lift from the water level, the pressure the pump must produce, and resistance as water moves through the piping.
You do not need to guess horsepower before gathering that information. The usual path is to work out what the system asks of the pump, then compare that duty point with the pump manufacturer’s performance data.
A useful sizing sequence looks like this:
- Estimate the home’s peak water demand in GPM.
- Find or measure the pumping water level.
- Decide what operating pressure the system needs.
- Convert that pressure to feet of head.
- Add friction loss through the pipe and fittings.
- Compare the resulting GPM and TDH with pump curves.
- Check that the selected flow also makes sense for the well’s yield.
How Much GPM Does a House Need?
Household demand is not the same from one property to the next. Bathroom count, residents, appliances, outdoor faucets, irrigation, and simultaneous use all change the flow requirement.
Penn State’s planning guidance suggests at least 6 GPM for most single-family homes, while its reference table increases the suggested flow as the number of bedrooms and bathrooms rises. A three-bedroom home with two bathrooms, for example, is listed at 12 GPM in that planning table. These figures are useful references rather than universal pump ratings.
Outdoor demand can change the picture quickly. Running irrigation while showers and appliances are in use may call for more flow than indoor fixtures alone.
What Does Total Dynamic Head Include?
For a typical residential well system, a simple working expression is:
TDH ≈ pumping lift + pressure head + friction loss
Friction comes from moving water through the drop pipe and the rest of the plumbing. Pipe diameter, length, material, fittings, valves, filters, and flow rate all have an effect. A smaller pipe usually creates more resistance when the same amount of water is pushed through it.
The exact calculation can become more involved on systems with unusual elevations, treatment equipment, storage tanks, or other components. Those conditions belong in the sizing work rather than being ignored in favor of a horsepower-by-depth rule.
Converting Pressure Into Feet of Head
Pump curves usually express pressure as feet of head. For water under standard conditions, 1 psi is about 2.31 feet of head.
So:
50 psi = about 115.5 feet of head
60 psi = about 138.6 feet of head
That 10 psi increase adds roughly 23 feet of pressure head. A system operating at 40/60 therefore asks more of the pump at cutoff than a similar system operating at 30/50.
A Simple TDH Example
Suppose the pumping water level is 120 feet below the pressure tank. The system is expected to reach 60 psi, and the estimated pipe friction at the desired flow is 12 feet.
The rough calculation is:
120 + 138.6 + 12 = 270.6 feet of TDH
Now suppose the house needs 10 GPM. The useful sizing point is roughly 10 GPM at 271 feet of head. At that stage, you can open the manufacturer’s pump curve and look for equipment that operates in the needed range. Notice what did not happen in that example: horsepower was not chosen first.
Why the Pump Curve Matters More Than a Depth Chart
A pump curve shows how much water a particular pump can move as head changes. Generally, available flow falls as the pump has to work against more head.
The difference between pumps with the same horsepower can be substantial. In one current Franklin Water residential series, a 3/4 HP 10 GPM model has a listed shutoff head of 338 feet, while a 3/4 HP 20 GPM version is listed at 190 feet. Those are pumps from the same manufacturer with the same motor horsepower but very different flow/head designs.
That example is also why the published shutoff head should not be treated as a recommended operating depth. Normal pump selection is based on the required flow at the actual system head, not the no-flow shutoff point. If the current pump model or well data are unavailable, a well pump inspection or service visit can help establish the missing information.
Jet Pump or Submersible Pump?
Choosing between a jet pump or submersible pump depends largely on the well setup and water level. Jet pumps are commonly used for shallow wells and draw water through a suction line, while submersible pumps sit inside the well and push water toward the house. The U.S. Environmental Protection Agency notes that jet pumps are commonly used for shallow wells of about 25 feet or less, while submersible pumps are commonly used in deeper private wells.
Shallow Well Jet Pumps
A shallow well jet pump is used where the vertical suction lift is relatively small. The familiar limit of roughly 25 feet comes from the practical limits of atmospheric pressure and suction, not from a shortage of motor horsepower.
Putting a larger motor on a shallow-well arrangement does not make those suction limits disappear. A deeper water level usually calls for a different pump configuration.
Deep Well Jet Pumps
Deep well jet systems use a different arrangement, often placing the jet assembly down in the well. Pump, jet, piping configuration, and manufacturer data all affect how much water the system can move.
Older installations may still use this type of setup, so replacing the pump without identifying the existing piping can lead to the wrong equipment choice.
Submersible Well Pumps
Submersible pumps are common in deeper residential wells because they push rather than pull the water. Residential models are available across a wide range of GPM and horsepower combinations. Franklin Water’s current residential lines, for example, include models from 1/2 HP upward with several separate flow ranges.
Casing size, voltage, wiring, control box requirements, water level, well yield, and the pump curve still have to match the installation.
How Pressure Switches and Pressure Tanks Change the Picture
The pressure switch tells a conventional well system when to start and stop the pump. The pressure tank stores a usable amount of pressurized water between those starts. Neither component determines horsepower by itself, but both affect how the pump operates once it is installed.
A pump that works acceptably at one pressure range may have less flow available after the cutoff pressure is raised. The tank also has to be set up for the switch range in use.
30/50 vs. 40/60 Pressure
With a 30/50 switch, the pump generally starts around 30 psi and stops around 50 psi. A 40/60 switch raises both points by 10 psi.
Some homeowners prefer the stronger fixture pressure associated with the higher range. The pump still has to be capable of reaching 60 psi after pumping lift and pipe friction are added. Raising the switch setting on a marginal pump can leave it running for a long time or unable to reach cutoff.
Pressure Tank Precharge
Tank precharge also changes with the pressure-switch setting. Amtrol instructs users of its well tanks to set precharge 2 psi below the pressure-switch cut-in setting. Before checking or adjusting precharge, shut off electrical power to the well pump and drain the system until the water-pressure gauge reads 0 psi. For those tanks, that corresponds to 28 psi for 30/50 and 38 psi for 40/60.
Manufacturer instructions for the actual tank should take priority. A tank with the wrong precharge can create pressure problems that may be mistaken for a pump horsepower problem.
A pressure tank evaluation is useful when the pump cycles frequently, pressure swings have become noticeable, or the tank and switch settings are unknown.
Bigger HP Is Not Always Better
A higher-horsepower pump makes sense when the system’s required flow and head call for it. Going bigger without doing the sizing work can create a pump that is poorly matched to the well, pressure tank, piping, or controls.
An undersized pump can struggle during heavy use or take too long to reach cutoff pressure. An oversized pump may refill the pressure tank very quickly, which can contribute to frequent starts when the rest of the system is not sized around that output.
Short cycling has other possible causes, though. Amtrol lists rapid cycling as a possible sign of pressure-tank trouble, so repeated starting should not automatically be blamed on the pump being too large.
The Well Still Has a Limit
A pump can only use the water the well supplies. Penn State defines well yield as the maximum pumping rate that can be maintained without drawing the water level below the pump intake.
If household demand is higher than the well can sustain, installing more horsepower does not create more groundwater. Low-yield wells may need a system that stores water gradually and supplies it to the home during periods of higher demand.
This is also why a larger pressure tank alone is not a substitute for adequate well yield. Pressure storage and groundwater production solve different problems.
Should I Replace My Current Pump With the Same HP?
The old pump’s horsepower is a useful clue, especially when the system worked well for years. Still, matching the HP label does not prove that a replacement pump has the same performance. Model, flow range, number of stages, voltage, controls, and pump curve can differ.
A replacement is also a good time to check whether the property has changed. A new bathroom, irrigation system, water-treatment equipment, higher pressure setting, or a change in well performance can shift the operating requirements.
When the old pump model is readable, its original performance information can be compared with the proposed replacement. If that information is gone, actual system measurements provide a stronger basis than guessing from motor horsepower.
What About a 500-Foot Well?
A 500-foot well could use very different pumps from one property to another. Total depth only tells you how far the borehole extends. It does not tell you where the water stands while pumping or how much flow the home needs.
Say one 500-foot well has a pumping level of 130 feet and serves a small household. Another has a pumping level near 300 feet, higher peak demand, and a 40/60 pressure setting. Those systems do not present the pump with the same job even though their total depth is identical.
For a deep well, gather the pumping water level, required GPM, pressure setting, pipe information, well yield, and pump setting before deciding on horsepower. Then use the pump curve to see which model can meet that combination.
Choose the Pump for the Well and the House
The right well pump is selected from the job it has to perform, not from one number on the motor. Start with household GPM, pumping water level, pressure, friction, and well yield. Calculate the system’s approximate TDH, then use the manufacturer’s pump curve to see which pump can meet that demand without relying on a generic depth-to-horsepower chart.
If you do not have the well measurements or pump information needed for sizing, Housatonic Valley Well Pump Services can evaluate the system and help determine what pump fits the well and household demand. Request a well pump evaluation or quote.
FAQs
What Is the Difference Between a 1/2 HP and 3/4 HP Well Pump?
A 3/4 HP motor has a higher power rating than a 1/2 HP motor, but that does not mean every 3/4 HP pump delivers more usable water in every well. The pump end and number of stages affect the flow/head relationship, so compare the actual performance curves at your required GPM and TDH. If a 1/2 HP model already meets the system requirement, moving up in horsepower is not automatically an improvement.
Is a 30/50 or 40/60 Pressure Switch Better?
Neither setting is better for every home. A 40/60 switch provides a higher pressure range, but the pump must overcome about 23 additional feet of pressure head at 60 psi compared with 50 psi. The pump curve, tank precharge, plumbing, and desired household pressure should all support the change before the switch is adjusted.
What Size Pump Should I Have if My Well Is 500 Feet Deep?
A 500-foot well depth is not enough to choose the pump. The sizing work also needs the pumping water level, required GPM, pressure, friction loss, well yield, pump setting, and a manufacturer’s pump curve. Water in a 500-foot well may stand far above the bottom, so the pump does not automatically have 500 feet of pumping lift.
How Deep Can a 3/4 HP Well Pump Go?
There is no single maximum depth that applies to every 3/4 HP pump. Different models are built for different combinations of flow and head, and even pumps from the same manufacturer can have noticeably different performance at the same horsepower. Match the specific 3/4 HP pump curve to the required GPM and TDH rather than choosing it from total well depth.
Is a Bigger HP Well Pump Better?
More horsepower is useful only when the system needs the extra capability. A pump that is too small may fall short on flow or pressure, while excessive output can be a poor match for the well, tank, piping, or controls. The better target is a pump that operates properly at the home’s required flow and head.
Should I Replace My Old Well Pump With the Same Horsepower?
Using the same HP can make sense when the old pump was correctly sized and the system has not changed, but confirm more than the motor label. Compare the old and new pump curves, flow range, voltage, controls, pressure setting, and well conditions. Changes in household demand or pumping water level can also change what the replacement pump needs to do.