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What Size Well Pressure Tank Do You Need?
Keep your shower pressure pumping with the right tank
Photo: Aaron MCcoy / The Image Bank / Getty Images
Photo: Aaron MCcoy / The Image Bank / Getty Images
Highlights
Well pressure tanks prevent the pump from turning on and off rapidly.
You can choose between 20-, 30-, 50-, 85-, and 120-gallon tanks.
To determine what size you need, multiply the flow rate by the minimum run time.
It’s better to buy a well pressure tank that’s too big than a tank that’s too small, but a pro can help you find the perfect size.
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Well pressure tanks are largely responsible for maintaining the water pressure within your home. Whether you’re replacing an old one or installing a new one, choosing the correct well pressure tank size for your home will help your well system work smoothly and efficiently. Read on to learn how to size a pressure tank and choose the right one for your needs.
How Does a Well Pressure Tank Work?
A well water pressure tank is one of the key components of your well system, along with the pressure switch and the pump. It helps regulate your water pressure by storing water and sending it to your home when you turn on a faucet or flush a toilet.
Roughly one-third of the tank holds water, while the rest holds compressed air. The compressed air creates pressure in the tank and pushes up the water into your sinks and showers. This prevents the well pump from having to turn on and off every time a faucet is opened.
A pressure switch monitors the pressure within the tank. It lets the pump know when to turn on or off depending on the level of pressure.
Calculating the Tank Size You Need
There are five sizes of residential pressure tanks for water wells. You can choose between 20, 30, 50, 85, and 120 gallons.
The size you need depends on the specifics of your well, including:
Its depth
Its location
The pump type
The water use
To determine what size you need, you’ll need to calculate the drawdown. The drawdown is the amount of usable water in the tank and can be calculated using the flow rate and minimum runtime of the pump.
The flow rate is often tested when a new well is drilled and refers to how many gallons of water are produced by the pump every minute.
The minimum run time refers to the time it takes for the pump to get to the desired drawdown capacity. Follow these rules of thumb to determine the run time:
A flow rate of 10 gallons per minute or under should produce one gallon per minute of run time.
A flow rate of over 10 gallons per minute should produce 1.5 gallons per minute of run time.
A flow rate of over 20 gallons per minute should produce two gallons per minute of run time.
To calculate your tank size:
Multiply your flow rate by the minimum run time
That will equal the drawdown capacity
So, if you had a 10 GPM flow rate and a minimum run time of one GPM, your drawdown capacity would be 10 gallons.
Choosing a Tank
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Once you’ve verified the flow rate, minimum run time, and calculated the drawdown, you can choose your tank.
| Tank Size | Drawdown Volume |
|---|---|
| 20 gallon | 6 gallons of drawdown |
| 30 gallon | 9 gallons of drawdown |
| 50 gallon | 14 gallons of drawdown |
| 85 gallon | 25 gallons of drawdown |
| 120 gallon | 36 gallons of drawdown |
So, using the drawdown size calculated above at 10 gallons, the home would need at least a 50-gallon tank since you want to size up instead of sizing down. A larger pressure tank often lasts longer due to having fewer pump cycles. They may, however, be less cost-effective and take up a larger space.
A tank that is too small will wear out quickly as it cycles too fast. This also means you may have to replace the tank more often. The cost of a new well pressure tank can range from $125 to $500.
If you run into any trouble calculating the drawdown size or feel uneasy about your tank size choice, reach out to a local well pump contractor. They’ll be happy to help you calculate the well pressure tank size you need and install it for you.
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