A well pressure tank delivers a steady supply of well water into your home, meaning that you always have enough water pressure – even during times of peak use.
Incorrectly sizing your well pressure water tank could affect the performance of your well pump.
In this guide, we’ve shared how to properly size a pressure tank in your home.
📌 Key Takeaways:
- Well pressure tanks use compressed air to push down on the stored water, creating water pressure.
- Installing a properly sized well pressure tank means you’ll always have access to water on demand and your well pump won’t be overused.
- When sizing a pressure tank, consider factors including your well pump’s size and output, your water usage and household size, the distance from the well pump to the pressure tank, and the type of well pump you own.
Table of Contents
📐 What Sizes Do Well Pressure Tanks Come In?
The standard sizes for well pressure tanks are:
- 20 gallons
- 30 gallons
- 50 gallons
- 85 gallons
Some manufacturers also sell extra-large pressure tanks of 120 gallons. This is usually as big as it gets for residential use. Remember, around two-thirds of the tank volume is compressed air, so you’d need a huge tank to hold any more water than this.
Most people need a 20-50-gallon tank, but this all depends on the tank’s drawdown capacity.
📋 How To Size A Well Water Pressure Tank
There are a few things to know when sizing a pressure tank:
- Your pump’s flow rate: Find out the flow rate of your well pump in gallons per minute (GPM), which measures how many gallons of water the pump can deliver per minute. This information should be in your well records from initial testing after the well was drilled.
- Minimum run time: You also need to know the minimum time that your well pump will run.
- Pressure switch setting: When shopping for pressure tanks, note their pressure switch settings. There are two common settings – 30/50, and 40/60. The first number is the pressure at which the well pump switches on, and the second number is the pressure at which the pump switches off. The pressure tank drawdown capacity is affected by the pressure setting.
What’s your goal when selecting a tank size? To ensure that the tank’s drawdown capacity – the amount of usable water in the tank that’s stored between high and low pressure – is suitable for your well pump pressure and size.
Here are some guidelines for a well pump’s minimum run time based on its recorded flow rate:
- Pump flow rate of 0-10 GPM: 1.0 GPM of run time
- Pump flow rate of 10-20 GPM: 1.5 GPM of run time
- Pump flow rate of 20+ GMP: 2.0 GPM of run time
Use this moment to make a note of your pump’s flow rate and run time.
Now you can work out the pressure tank drawdown capacity you need. Just use the following equation:
Pump flow rate x minimum run time = drawdown capacity
We’ve shared an example of how this might look with real figures below:
Pump flow rate of 10 GPM x minimum run time of 1.5 GPM = 15-gallon drawdown capacity
In this case, you’ll need a well pressure tank that has a drawdown capacity of at least 15 gallons. Most people would go for a 50-85-gallon tank.
📊 Factors To Consider When Sizing A Pressure Tank
When sizing a tank for your well, also consider the following factors.
Well Pump Size & Output
We’ve discussed well pump size and output already, so we’ll keep it short.
The size and output of your well pump determine the speed and volume of water that’s delivered into the tank. The amount of water that the pump produces per minute determines its minimum run time.
How do you know the size and the output rate of your well pump? You should be able to find the flow rate information in your well records, and you can use this to work out the minimum run time.
You can then use this information to determine the suitable pressure tank size for your home.
Water Usage & Household Size
Your water usage and household size are also important to consider when sizing a well tank.
You need a tank with a big enough water storage capacity to keep you sustained with enough water, even during peak use.
If the tank is too small, you may experience drops in pressure as you run out of water and wait for the well pump to deliver water back into the tank. The pump will also need to work harder since it’ll switch on and off more frequently to replenish the water in a smaller tank volume.
The average person uses around 145 liters or 38 gallons of water per day. You could estimate your household water usage based on all your hand-washing, dishwashing, and showering activities, or use a water use calculator like this one.
Distance From Well To Pressure Tank
The distance from the well pump to the pressure tank affects the pressure once the water reaches the tank. The further the distance between the pump and the pressure tank, the more pressure will be lost.
If your well is located further away from the pressure water tank, you might need to compensate for the reduced pressure with a larger tank that has a higher drawdown capacity.
Submersible Vs Jet Pump
The type of pump used in your well can also affect the size of the pressure tank needed.
Submersible pumps operate around 30% faster than jet pumps, which means they pump a larger volume of water. It often makes sense to combine a submersible pump with a larger pressure water tank.
Jet pumps, on the other hand, don’t require such a large tank because they generally move smaller volumes of water per minute.
✅ The Importance Of A Properly Sized Pressure Tank
Wondering why your new pressure tank size matters?
There are a couple of reasons why you should make sure you buy the right-size pressure tank for your home:
To Give You Access To Water On Demand
With any well system, you want to make sure you’re delivered enough water at all times – even during peak usage.
If your pressure water tank is too small, you might end up experiencing pressure drops as your tank empties and the pump struggles to refill it on time to keep up with your needs.
A properly sized tank, on the other hand, will have a large enough tank volume to deliver all the water you need. It’s always best to get a slightly larger tank than you think you’ll need for that reason.
To Reduce How Often The Pump Turns On And Off
A well pump works in tandem with the pressure water tank.
When the pressure in the tank drops below a certain number, the pressure switch sends a signal to the pump, and the pump turns on. Then, once a certain pressure in the tank has been achieved, the pump shuts off.
If your pressure water tank is too small for your water needs, the pump will need to turn on and off frequently to refill the tank, causing the motor to burn out at a faster rate and shortening its lifespan.
❔ Well Water Pressure Tank Sizing: FAQ
Can you oversize a well pressure tank?
Yes, it’s possible to oversize a well pressure tank in your home. An oversized well pressure tank might be too demanding for your well pump, requiring it to run for long periods. But, if your well pump is properly sized to your well make-up, this shouldn’t be an issue. In short, there are more problems that come from an undersized pressure tank than an oversized tank.
Is a 20 gallon pressure tank big enough?
A 20-gallon tank has 6 gallons of drawdown, which means it’ll only work if your well pump has a flow rate of less than 7 GPM. If your well pump’s flow rate is higher than this, you’ll need to size up with the pressure tank.
What happens if pressure tank is too small?
If your well pressure tank is too small, it’ll need a lot of pump cycles (when the pump switches on to deliver water into the tank, then switches off again) because the rate of water usage in the tank will be too fast. As a result, the well pump will use more electricity and may need early repair or replacement. That’s why it’s so important to have a properly sized pressure tank.
Will a bigger pressure tank give me more water pressure?
No. A pressure tank has an adjustable pressure, and increasing the tank won’t give you more water pressure in your home. A larger tank will simply produce more gallons of drawdown, meaning that the well pump will need to have a higher pressure rating to effectively deliver water into the tank.
What is a well pressure tank’s pressure switch setting?
The pressure switch setting in a pressure water tank is two numbers: the cut-in pressure and the cut-out pressure. Pressure switch settings, depends on the tank size, and can be 20/40, 30/50, and 40/60. Let’s say a tank has a 40/60 pressure switch. When the tank is full, the pressure is 60 PSI. But as the water is gradually delivered to your plumbing system, the pressure drops. Once this pressure reaches 40 PSI, the pump will be activated to draw more water into the tank. The pump shut off will occur when the pressure in the tank achieves 60 PSI once more.