Do I Need a Larger Pressure Tank for My Well System?

Larger Pressure Tank for well system

A pressure tank is an essential part of a private well system. It stores pressurized water, helps maintain steady household pressure and prevents the well pump from starting every time a small amount of water is used.

When a pressure tank is too small, the pump may start and stop more frequently than necessary. This is known as short cycling, and it can increase wear on the pump motor, pressure switch and other system components.

A larger pressure tank can reduce pump cycling and provide more usable water between pump starts—but bigger is not automatically necessary for every home.

The correct tank should be selected according to the pump’s flow rate, desired minimum run time and pressure-switch settings—not simply by the number of bathrooms or the tank’s advertised gallon capacity. Manufacturers commonly size conventional pressure tanks using the pump’s delivery rate multiplied by the desired minimum run time.

What Does a Pressure Tank Actually Do?

A modern pressure tank contains water and compressed air separated by a bladder or diaphragm.

When the well pump runs, water enters the tank and compresses the air above or around the bladder. When a faucet is opened, the compressed air pushes the stored water into the home’s plumbing.

The pump remains off until the pressure falls to the pressure switch’s cut-in setting.

For example:

• A 30/50 switch starts the pump at approximately 30 PSI and stops it at 50 PSI.

• A 40/60 switch starts the pump at approximately 40 PSI and stops it at 60 PSI.

The amount of usable water released between cut-out and cut-in is called drawdown.

A pressure tank’s advertised size is not its usable-water capacity. A tank labelled as 20, 32 or 44 gallons holds considerably less usable water because part of its internal volume must remain filled with compressed air.

What Changes When You Install a Larger Pressure Tank?

A larger tank generally provides more drawdown.

That means the home can use more stored water before the pressure drops to the pump’s cut-in setting. Once the pump starts, it will normally run longer to refill the larger tank.

The main goal is not simply to store more water. It is to provide healthy pump cycles with fewer starts and adequate run time.

Manufacturers note that greater drawdown reduces the number of pump starts and can extend the life of the pump and water-system components.

Advantages of Upgrading to a Larger Pressure Tank

1. Fewer Pump Starts

Every pump start places electrical and mechanical stress on the system.

During startup:

• The motor draws increased current

• The motor windings begin heating

• Bearings and rotating components accelerate

• The pressure-switch contacts close under load

• Control-box components are activated

A larger tank supplies more water between cycles, allowing the pump to start less frequently.

Reducing unnecessary starts can help protect the pump motor, pressure switch and electrical controls.

2. Longer Pump Run Times

Most conventional well pumps benefit from running for a reasonable amount of time rather than starting and stopping every few seconds.

A larger pressure tank takes longer to refill. This can provide a more complete operating cycle and reduce rapid cycling.

Common sizing guidance uses approximately:

• A minimum one-minute run time for many pumps up to 3/4 horsepower

• A minimum two-minute run time for many pumps larger than 3/4 horsepower

The pump manufacturer’s instructions should always take priority because allowable starts and recommended run times vary by motor and control system.

3. More Water Available Before the Pump Starts

A larger tank provides more drawdown.

This can be helpful when using small amounts of water for:

• Washing hands

• Flushing a toilet

• Filling a drinking glass

• Briefly running a faucet

• Producing water through an ice maker

• Supplying a small appliance

  
  

With adequate drawdown, these small demands may be supplied without starting the well pump every time.

4. Reduced Pressure-Switch Wear

A conventional pressure switch opens and closes whenever the pump starts and stops.

Frequent operation can eventually cause the electrical contacts to become burned, pitted or damaged.

By reducing the total number of cycles, a larger tank may help extend pressure-switch life.

5. Better Support for Periods of Intermittent Demand

A larger tank can be useful when several small water demands occur close together.

Examples include:

• Toilets being used repeatedly

• Short faucet use during meal preparation

• An ice maker and dishwasher drawing water

• Small water-treatment demands

• Frequent handwashing in a busy home

The stored drawdown may satisfy some of these demands without immediately starting the pump.

6. A Small Reserve During a Power Interruption

The water stored between the current system pressure and the pressure switch’s cut-in point may remain available when the power goes out.

A larger tank can provide more stored water than a smaller tank, but it should not be treated as a complete emergency-water-storage system.

Once pressure falls and the tank empties, the well pump cannot refill it without electricity.

7. Flexibility for Future Household Demand

A larger tank may provide useful additional capacity when a home adds:

• Another bathroom

• A larger family

• Outdoor watering

• A treatment system

• Livestock watering

• A workshop or secondary building

• Higher household water use

However, the pump and well must also be capable of meeting the increased demand. A larger pressure tank cannot create additional well yield or pump capacity.

Disadvantages of Installing a Larger Pressure Tank

1. Higher Purchase and Installation Cost

Larger tanks cost more and may require:

• A larger tank tee

• New fittings

• Additional support

• Changes to nearby plumbing

• Relocation of the pressure switch or gauge

• Additional labour

• Modifications to the mechanical room

The improvement should justify the additional cost.

2. More Space Is Required

Large pressure tanks can occupy substantial floor space and may be difficult to install in:

• Crawlspaces

• Small pump rooms

• Utility closets

• Low basements

• Cottages with limited mechanical space

• Existing treatment-system areas

The tank must remain accessible for inspection, pressure checks and eventual replacement.

3. The Pump May Run Longer Per Cycle

Longer pump operation is usually an advantage when correcting short cycles, but the pump must be capable of operating properly for the increased run time.

A weak pump, restricted waterline or low-producing well may take a long time to refill a very large tank.

If the well cannot recover quickly enough, an oversized tank could contribute to extended drawdown from the well during each cycle.

4. Pressure Recovery May Take Longer

After a large amount of stored water has been used, the pump must refill the larger tank before reaching cut-out pressure.

The household still receives water while the pump is running, but the system may take longer to return to full shutoff pressure.

This is not usually a concern with a properly sized pump. It can become noticeable when the pump is worn, undersized or operating near its pressure limit.

5. A Larger Tank Will Not Increase the Pressure-Switch Settings

Installing a larger pressure tank does not automatically increase household pressure.

A 30/50 system will still operate between approximately 30 and 50 PSI. A 40/60 system will still operate between approximately 40 and 60 PSI.

The larger tank changes how much water is available between pump cycles—not the operating-pressure range.

6. It Will Not Correct an Existing System Defect

A larger tank will not repair:

• A leaking check valve

• A failed foot valve

• An underground waterline leak

• A clogged pressure-switch nipple

• Incorrect switch settings

• A weak or worn pump

• Low well yield

• A damaged tank bladder

• A running toilet

• A water-treatment drain leak

The existing system should be diagnosed before upgrading.

7. Bigger Is Not Always Better

Once the tank provides sufficient drawdown and minimum pump run time, installing a dramatically larger tank may provide only a limited additional benefit.

It may reduce starts further, but it also requires more space and money.

The goal is to choose an appropriately sized tank—not necessarily the largest tank that can fit through the door.

Do You Need a Larger Pressure Tank?

You may benefit from a larger tank when:

• The pump runs for only a few seconds per cycle

• The pump starts after very little water is used

• The existing tank is undersized for the pump’s flow rate

• The home experiences frequent pump cycling

• The pressure switch operates repeatedly during normal water use

• A high-output pump is connected to a small tank

• Household water demands have increased

• The existing tank requires replacement anyway

• You want fewer pump starts and longer cycles

• The present tank does not provide the manufacturer’s recommended drawdown

You may not need a larger tank when:

• The existing tank is properly sized

• Pump cycles are already long and stable

• The tank’s precharge is correctly adjusted

• The pump does not short cycle

• The existing problem is caused by a leak or failed valve

• The home uses a variable-speed constant-pressure system

• The pump manufacturer specifies a different tank arrangement

First Confirm That the Existing Tank Is Working Properly

A tank that appears too small may actually have:

• Incorrect air pre-charge

• A ruptured bladder

• A leaking air valve

• A waterlogged condition

• A blocked tank connection

• Incorrect pressure-switch settings

For most conventional bladder or diaphragm tanks, the pre-charge is normally set 2 PSI below the pressure switch’s actual cut-in pressure, with the pump turned off and all water pressure drained from the system.

Typical examples are:

• 30/50 switch: 28 PSI tank pre-charge

• 40/60 switch: 38 PSI tank pre-charge

An incorrectly charged tank can lose much of its intended drawdown and make an adequately sized tank behave like a much smaller one.

How to Choose the Correct Pressure-Tank Size

Tank sizing should begin with the pump and operating system—not the number printed on the old tank.

Step 1: Determine the Pump’s Actual Delivery Rate

Find the approximate rate at which the pump delivers water to the pressure tank in gallons per minute.

This information may be available from:

• The pump model

• The manufacturer’s pump curve

• Original installation records

• A measured flow test

• A pump-system performance test

Do not assume pump flow from horsepower alone.

A 1/2-horsepower pump might be designed for 5, 10, 15 or more gallons per minute depending on the pump model, well depth and total dynamic head.

Proper pump selection depends on both the required flow and the total head the pump must overcome.

Step 2: Determine the Desired Minimum Run Time

The minimum run time is how long you want the pump to operate after it starts.

A common conventional guideline is:

• Approximately one minute for many pumps up to 3/4 horsepower

• Approximately two minutes for many pumps larger than 3/4 horsepower

Always confirm the motor manufacturer’s requirements.

Step 3: Calculate the Required Drawdown

A common basic sizing formula is:

Required drawdown = pump flow rate × minimum run time

Example 1

A 10 GPM pump with a desired one-minute run time:

10 GPM × 1 minute = 10 gallons of required drawdown

Example 2

A 15 GPM pump with a desired two-minute run time:

15 GPM × 2 minutes = 30 gallons of required drawdown

Pentair describes a similar conventional rule of providing approximately one gallon of drawdown for each gallon per minute of pump capacity when using a one-minute minimum cycle.

Step 4: Account for the Pressure-Switch Setting

A tank’s drawdown changes with the operating-pressure range.

The same tank generally provides different drawdown at:

• 20/40 PSI

• 30/50 PSI

• 40/60 PSI

• 50/70 PSI

Higher operating pressures compress the air differently and usually reduce the usable drawdown available from a given tank.

That means a tank model that is adequate for a 30/50 system may not provide the same usable capacity on a 40/60 system.

Always select the tank using the manufacturer’s drawdown table for the actual switch setting.

Step 5: Select a Tank With At Least the Required Drawdown

Once the required drawdown is known, compare it with the manufacturer’s specifications.

Do not select a tank solely by its total-volume rating.

For example, a tank advertised as a 44-gallon tank does not supply 44 gallons of usable drawdown. The actual drawdown may be only a fraction of the total capacity, depending on the pressure settings and pre-charge.

Choose a model whose listed drawdown meets or exceeds the calculated requirement.

Step 6: Consider the Home’s Actual Use

Pump flow and minimum run time are the technical starting points, but the home’s needs also matter.

Consider:

• Number of occupants

• Number of bathrooms

• Simultaneous fixture use

• Large bathtubs

• Laundry demand

• Outdoor watering

• Livestock

• Water-treatment backwash requirements

• Secondary buildings

• Seasonal peak usage

• Expected future additions

A larger tank may be worthwhile when it provides better operation during frequent intermittent water use.

However, the tank does not replace the need for a properly sized pump and adequate well yield.

Tank Sizing Examples

These examples illustrate the process only. The final model must be chosen from the manufacturer’s drawdown chart.

10 GPM Pump With a One-Minute Minimum Run Time

Required drawdown:

10 GPM × 1 minute = 10 gallons

Choose a tank that provides at least 10 gallons of drawdown at the actual pressure-switch setting.

12 GPM Pump With a One-Minute Minimum Run Time

Required drawdown:

12 GPM × 1 minute = 12 gallons

Choose a tank that provides at least 12 gallons of drawdown at the selected pressure range.

15 GPM Pump With a Two-Minute Minimum Run Time

Required drawdown:

15 GPM × 2 minutes = 30 gallons

Choose a tank or combination of tanks that provides at least 30 gallons of drawdown.

20 GPM Pump With a Two-Minute Minimum Run Time

Required drawdown:

20 GPM × 2 minutes = 40 gallons

This system may require a large tank or multiple tanks to provide adequate conventional drawdown.

Can You Install Two Pressure Tanks?

Yes. Multiple properly connected pressure tanks can provide combined drawdown.

This can be useful when:

• One large tank will not fit through the entrance

• Ceiling height is limited

• Existing equipment blocks the preferred location

• Additional capacity is being added to a working tank

• Weight or floor-space distribution matters

The tanks should:

• Be rated for the system pressure

• Have matching precharge settings

• Be connected so they experience the same system pressure

• Be installed according to manufacturer requirements

• Remain accessible for service

Adding a second tank does not require a second pressure switch when both tanks operate as part of the same pressure system.

What About Constant-Pressure Systems?

Variable-frequency drive systems operate differently from conventional fixed-speed pump systems.

A constant-pressure controller changes pump speed to match water demand. These systems are often designed to work with a much smaller pressure tank because the drive—not large stored drawdown—controls pump operation.

Some variable-speed products are specifically designed for small tanks, although certain systems can also operate with existing larger tanks.

Do not apply conventional pressure-tank sizing rules to a constant-pressure system without checking the drive manufacturer’s instructions.

Installing an oversized tank on certain drive systems may change how quickly the system responds, while installing too small a tank can create control issues if it does not meet the manufacturer’s minimum requirement.

Does a Larger Tank Improve Household Water Pressure?

Not directly.

Pressure is primarily controlled by:

• Pressure-switch settings

• Pump capability

• Well depth

• Pipe size and condition

• Plumbing restrictions

• Water-treatment equipment

• Elevation differences

• Flow demand inside the home

A larger tank may make pressure changes feel slower because it supplies more water between cut-in and cut-out.

However, it will not turn a 30/50 system into a 40/60 system or repair poor pressure caused by a weak pump or restricted waterline.

Will a Larger Tank Increase Well Capacity?

No.

A pressure tank does not make the well produce more water.

It only stores water already delivered by the pump.

A low-yield well may require other solutions, such as:

• Pump protection

• Low-water cut-off controls

• A storage cistern

• Controlled well recovery

• Demand management

• A properly designed transfer-pump system

Installing a huge pressure tank cannot overcome a well that does not recover fast enough to supply the household.

Should You Replace a Working Small Tank?

Replacing a working tank may be worthwhile when:

• It is demonstrably undersized

• The pump cycles too frequently

• Household water use has increased

• The pump has been upgraded

• The system has a history of switch or motor failure

• You are already rebuilding the tank-tee assembly

• The additional drawdown provides a meaningful operational benefit

Replacement may not be necessary when the system already has acceptable pump run times and cycle frequency.

A proper test can usually determine whether a larger tank would provide a genuine benefit.

The Bottom Line

A larger pressure tank can be an excellent upgrade when the existing tank does not provide enough drawdown for the pump.

The main advantages are:

• Fewer pump starts

• Longer pump cycles

• Reduced short cycling

• Less pressure-switch wear

• More stored water between cycles

• Potentially longer equipment life

The main disadvantages are:

• Higher cost

• More required space

• Longer refill periods

• More difficult installation

• Limited additional benefit once the system is already properly sized

The correct tank size is based primarily on:

1. The pump’s delivery rate

2. The required minimum pump run time

3. The pressure-switch setting

4. The tank manufacturer’s drawdown chart

5. The type of pump-control system

A larger tank can protect a properly operating system, but it cannot repair a weak pump, leaking valve, underground waterline problem or low-producing well.

Pressure-Tank Installation in Thunder Bay

Superior Water & Wells provides pressure-tank sizing, tank replacement, pressure-switch service and complete well-system troubleshooting throughout Thunder Bay and the surrounding area.

We serve rural homeowners, camps, cottages and lakefront properties throughout Shuniah, Neebing, Kakabeka Falls, Murillo, O’Connor, Nolalu, Pass Lake and the Highway 61 corridor.

Not sure whether your pressure tank is too small, incorrectly charged or beginning to fail?

Contact Superior Water & Wells for professional pressure-system testing and reliable rural water service.

Superior Water & Wells — Rural Water Done Right.