Is A 20 Gallon Pressure Tank Big Enough? (Find Out Now!)

Your home’s pressure tank is an essential piece to maintaining your well. These pressurized well tanks work to extend the life of your well pump by maintaining water pressure throughout your home and thwarting rapid on/off cycling of the pump. A pressure tank that is appropriately sized ensures that the water needs of your household are met and your pump is safeguarded against short-cycling.

If you currently have a 20-gallon pressure tank, you may find yourself wondering if this size is big enough. Many professionals recommend a larger tank so that the pump has less start and stop cycles.

However, in order to properly size your well pressure tank, you need to know the flow rate, minimum runtime, and the pressure switch setting. From these factors, you can determine the drawdown needed, which will tell you the necessary tank size to produce the preferred drawdown capacity.

In homes with a well, an electric pump extracts water from the well and distributes it throughout your home at a pressure high enough to service all of your fixtures with a sufficient amount of water. If the pump starts and stops too frequently, its lifespan can be depleted due to the constant stress of the startup process and preliminary current surge.

The purpose of a well pressure tank is to sustain the water pressure and protect the life of the well pump. It stores several gallons of water under pressure, permitting the tank to supply the fixtures in your home with water after the pump has shut off. With the tank, the pump does not have to cycle every single time water is needed, effectively extending its life.

When a pump turns on and off too frequently, this is referred to as “short-cycling.” Short cycling places an enormous amount of stress on your well pump and can even cause it to fail prematurely. By prolonging the time between the on and off cycles, a well pressure tank keeps your well pump from experiencing unnecessary wear and tear. It also stabilizes the water pressure in your home, that way your fixtures don’t spit or sputter as they are waiting for the pump to catch up.

With the properly sized well pressure tank, you can successfully avoid any expensive replacements of your well pump.

A well pressure tank is filled with a large volume of compressed air, whose purpose is to push pressurized water out of the tank and throughout your home. The tank’s inlet allows water into the base of the tank. Since air is compressible and water is not, the water that enters the tank will compress the air, pressurizing it.

Inside the pressure tank is a diaphragm, or bladder, which separates the water from the chamber of air. When the well pump hits maximum pressure and turns off, generally 50 to 60 PSI, this newly compressed air will push the water out of the tank when a fixture needs it.

The pressure tank does this without needing to turn the pump back on. Then, the pump will only turn back on to supply fixtures and refill the tank when the air pressure in the tank decreases to the minimum water pressure for the system, generally 30 to 40 PSI.

Your well pressure tank is designed to work in union with a pressure switch. The pressure switch’s purpose is to monitor the pressure within the tank. It will then notify the well pump when to turn on and off based on the increase and decrease of pressure inside the tank.

The majority of households are set up to work with a pressure tank that engages the pump at 30 pounds of pressure and then shuts it off at 50 pounds of pressure. There is a gauge located at the front of the pressure tank which indicates when the maximum pressure has been reached. At this point, the pressure switch will automatically shut off the pump.

Before you start sizing your well pressure tank, it’s important that you understand pressure tank drawdown. Drawdown refers to the amount of stored water that is available in the tank between the time that the pump turns on and off. As water exits the pressure tank, the pressure inside the tank drops.

For example, if you are using a 30/50 pressure switch, the pressure will continue to decrease until it reaches 30 PSI. At this point, the pressure switch will engage and activate the pump until the tank returns to 50 PSI. The volume of water that exists between 50 PSI and 30 PSI is the pressure tank drawdown.

Put simply, the drawdown describes the length of time that the pump is protected from shutting on and off. Not to be confused with the tank volume, as the total tank volume is a measure of the tank size that is needed to produce the desired drawdown.

Fortunately, many pressure tank manufacturers will supply you with a chart that indicates your drawdown capacity based on the pressure switch setting. With the above factors, you can easily determine the drawdown needed by multiplying the flow rate by the minimum run time.

As a general rule of thumb, any pump that operates at 10 gallons per minute (GPM) or less should produce one gallon per minute of run time. Anything above 10 GPM, should produce 1.5 gallons per minute of run time and if your flow rate is about 20 GPM, you may need multiple pressure tanks. These calculations would look something like this: