When public water service is not available at your home, an electromechanical system allows you to draw water out of a well. This system relies on a well pump to perform its critical role.
Regardless of the type of well pump your system uses, the size of the pump matters. An oversized pump will use too much energy and can reduce the system’s performance. On the other hand, an undersized pump simply won’t produce enough water to meet your home’s needs.
When reviewing well pump options, you’ll find confusing terms like GPM, horsepower, and depth. Through this guide, you’ll learn everything you need to know about flow rate, well depth, pressure needs, and pump types. You’ll also learn when to call a professional for assistance with your well pump.
Quick Takeaways
- Most homes need a pump that delivers 8–12 gallons per minute (GPM).
- Pump size depends on flow rate, well depth, and household demand.
- Horsepower alone does not determine proper sizing.
- Oversized pumps can cause short cycling.
- Undersized pumps lead to low water pressure.
- A professional load calculation prevents expensive mistakes.
What Size Well Pump Do I Need?
Most residential homes need a well pump that delivers 8–12 gallons per minute (GPM), depending on household size and water demand.
The correct size depends on your well depth, static water level, pressure requirements, and total fixture load. Pump horsepower must match both depth and required flow rate.
Step 1: Calculate Your Household Water Demand (GPM)
When calculating your household water demand, you’ll look at how many gallons per minute (GPM) you need at peak usage. Consider the flow rate for fixtures and appliances, such as your shower, sink, and washing machine. Determine how many of these features may need to draw water at the same time.
For example, in a three-bedroom home, you might need to run the washing machine while also having two showers in use. Consider all reasonable scenarios for water consumption to determine your peak demand range. Peak demand sizing ensures that you won’t experience inconvenient water pressure drops.
Step 2: Determine Your Well Depth and Water Level
Your water pump extracts water from the well, so factors like the static water level and the total well depth require consideration. The pump’s power to lift water from the bottom of the well to the surface is known as total dynamic head (or TDH).
TDH relates to pressure, pipe friction, and vertical lift requirements. A deeper well, for example, requires more horsepower to meet your system’s vertical lift requirements.
Step 3: Choose the Right Pump Type
There are three main types of pumps, and these are jet pumps, deep well jet pumps, and submersible pumps.
Jet pumps are installed above the well and use suction power to pull the water up. These are suitable for wells under 25 feet deep.
Deep well jet pumps work similarly, and they are designed to draw water from depths of 25 to 100 feet.
Submersible pumps are the standard for most Florida residential wells, and they are the most common for deeper wells. Like the other pumps, submersible pumps have a pump motor and water pump. They differ with an internal check valve, and they may not have a pressure tank.
Step 4: Match Horsepower to Depth and Flow Rate
The electric motor must have sufficient power to draw the water upward, so deeper wells require more horsepower. The horsepower for your well’s motor must match the performance curve.
This curve takes into account the pressure required to lift the water and the volume of water produced by the well.
Generally, you can use these guidelines to determine horsepower:
- ½ HP pump typical for shallow wells
- ¾ HP for moderate depth
- 1 HP+ for deeper wells or high demand
What Happens If You Choose the Wrong Size Pump?
Determining the appropriate horsepower for your pump is an essential part of your pump selection. What happens if you get the wrong size?
If the Pump Is Too Small
If your well pump is too small, you’ll likely experience low water pressure. You also might notice that your pump runs constantly. This results in premature motor wear and higher energy costs.
If the Pump Is Too Large
If the pump is too large for your needs, it’ll turn off and on frequently. This short cycling can damage the pressure tank over time. It also reduces the pump’s lifespan and creates higher electric bills.
How Tank Size Affects Well Pump Sizing
Your well’s tank size also affects pump sizing. Consider that a larger pressure tank holds more water, which reduces cycling.
However, the pump and the tank must be matched to avoid serious problems. For example, if you install a larger pump that is a mismatch for the current tank, you’ll run into repair problems and premature wear.
Do I Need a 1/2 HP, 3/4 HP, or 1 HP Well Pump?
When determining the appropriate well pump for your needs, several factors should be considered. For example, the typical home has one or two bathrooms. The pump typically needs to provide eight to 12 gallons of water per minute.
A ½ or ¾ HP pump motor is usually suitable. If you have a larger home with more bathrooms or have additional water consumption needs, such as an irrigation system, a 1 HP well pump may be a better option. A larger pump is also recommended for larger households as more people generally use more water.
Can I Just Replace My Pump With the Same Size?
It’s easy to assume that replacing an aging pump with a similarly sized pump is suitable. However, the current size may be incorrect. The household’s demands might have changed since the current pump was installed. For example, your household size could’ve grown, or you may have installed an irrigation system.
These changes in your needs might create pressure issues that need to be addressed with proper sizing. A professional re-evaluation is recommended prior to making your selection.
Signs Your Current Well Pump Is the Wrong Size
If your current well pump is the wrong size, you could notice several signs.
Some of these are:
- Low or fluctuating pressure
- Frequent short cycling
- Pump runs continuously
- Breaker trips
- Uneven water flow
- Excessive energy usage
Professional Well Pump Sizing and Installation
A correctly sized and professionally installed well pump ensures steady water pressure and will protect your pump’s lifespan. A trial-and-error approach is unnecessarily expensive and can be avoided by taking advantage of an installer with local expertise.
Your installer offers these services:
- System flow rate calculation
- Depth measurement
- Pressure testing
- Tank evaluation
- Performance curve matching
- Safe installation and calibration
Frequently Asked Questions
What size well pump do I need for a 3-bedroom house?
A typical 3-bedroom house with two bathrooms needs a ½ HP to ¾ HP pump. However, the number of people in the house, the presence of an irrigation system, and other factors must also be considered.
Is a 1 HP well pump better than a 3/4 HP pump?
A more powerful well pump isn’t always best. Using a more powerful pump could cause excessive wear, inflate energy costs, and have other negative consequences if the pump is appropriately sized for a home’s needs.
How many gallons per minute should a residential well pump produce?
A typical household with two bathrooms often uses eight to 12 gallons of water per minute. However, this is a general recommendation. The home’s needs should be professionally determined to avoid the downsides of improper sizing.
How do I know if my well pump is too small?
If your well pump is too small for your home’s needs, you might notice that your pump runs constantly or that water pressure is too low. These can lead to higher energy bills and premature motor wear.
Does a deeper well require a larger pump?
A deeper well requires a larger pump to draw the water upward. Insufficient water pressure is a common problem if the pump is insufficient for the well’s depth.
Get the Right Well Pump Size the First Time
Choosing the wrong size well pump affects everything from water pressure and pump longevity to cost and energy consumption. While a larger pump has a higher cost of installation, choosing the right size for your home’s needs results in long-term savings.
At Fort Myers Benjamin Franklin, we are the punctual plumber that you can count on for a professional evaluation. Schedule an appointment with us for all of your well pump installation and repair needs.