Having a well pressure tank in your home is one of the best investments you can make for your plumbing system. Well pressure tanks ensure that you have well water on demand and that your water pressure stays at a steady level. A pressure tank can also increase the lifespan of your well pump by taking some of the strain and pressure off of it. However, to receive these benefits, it's vital that you choose a well pressure tank that's the right size for your system.
There are several factors to consider when choosing the right size pressure tank for your well pump. You need to know the flow rate of your pump, its minimum runtime, and your pressure switch setting.
Once you know the answers to these three factors, you can determine the tank's drawdown time, which is the amount of water it can store between pump cycles. The drawdown time will then help you determine what size well pressure tank you need.
As you can see, there's a lot that goes into choosing the proper size well pressure tank. This article will explain each of these factors in detail and help you make the right choice for your well tank at your home or business.
How Does a Well Pressure Tank Work?
The job of a well pressure tank is to make life easier for your well pump and pressure switch. It does this by holding water so that it's ready to disperse throughout your house at a moment's notice. The bottom third of the pressure tank holds water, while the upper portion has compressed air that forces water through your plumbing pipes.
Your well pressure tank will also be equipped with a pressure switch that turns on and off as needed to send water out of the tank. Pressure switches are designed to turn on when the pressure inside the tank reaches a certain psi level and off when the pressure returns to an adequate level.
Factors to Consider When Sizing Your Well Pressure Tank
Now that you have a better understanding of how well pressure tanks work let's look at how to choose one that's the right size.
Flow Rate
Your flow rate refers to the number of gallons of water per minute your well pump produces.
Minimum Runtime
The minimum runtime refers to how long your well pump runs in a single cycle. In most cases, well pumps run for one minute. However, certain pumps can run for 90 seconds or even two minutes. Therefore, it's a good idea to find out from the pump manufacturer what the run time is or use a stopwatch to measure for yourself.
Pressure Switch Setting
The pressure switch setting refers to the pressure switch on your well pressure pump. The switch setting is the amount of pressure the tank has to be at for the switch to activate and fill with air. It also refers to the pressure at which the switch turns off. Pressure switches will have settings that feature a number followed by a colon and a second number.
For example, a 20:40 pressure switch will turn on when the pressure inside the well tank is at 20 psi and off when it reaches 40 psi. A 30:50 pressure switch will turn on when the pressure is at 30 psi and off when the pressure is at 50 psi.
Drawdown Time
Drawdown time or capacity refers to how much water is stored inside the tank from the time the pressure switch turns off until it turns back on. You will need to determine your drawdown capacity in order to know what size pressure tank you need.
How to Calculate the Proper Tank Size
Once you know your flow rate and minimum runtime, you can determine the drawdown volume. Here's a simple formula to use.
Minimum run time x flow rate = drawdown time.
For example, if your well pump has a minimum run time of 1 minute and a flow rate of 10 gallons per minute, multiply 10 x 1 to determine the drawdown time. In this scenario, your drawdown time is 10. Once you have your drawdown time, you can multiply that number by 3 to determine how big of a well pressure tank you need.
In this scenario, 10 x 3 = 30, which means you should have at least a 40-gallon well pressure tank. The reason you multiply by 3 is because only ⅓ of the well tank is filled with water. Pressure tanks come in either 20, 30, 50, 85, or 120 gallons, and you should always round up when calculating what size you need.
It's important to note that if you have a pressure tank that fills with more or less water than ⅓, you should multiply by that number instead. So, if ½ of your tank fills with water, multiply your drawdown time by 2. If ¼ of the tank fills with water, multiply your drawdown capacity by 4.
Downsides of Having a Tank That's Too Small
The worst-case scenario when you're choosing a well pressure tank is to choose one that's too small for your well pump. If this happens, the pressure switch on the tank will have to turn on and off more often, resulting in a shorter lifespan.
A good way to think of your pressure switch is that it will last for a certain number of cycles rather than years. So, the more often it cycles, the shorter the lifespan will be.
Downsides of Having a Tank That's Too Large
If you have to choose between a pressure tank that's too big or too small, you should always err on the side of too big. The bigger your pressure tank is, the less often it will have to cycle on and off, resulting in a longer lifespan. Additionally, having a pressure tank that's too big won't result in reduced water pressure or water.
The downside of an excessively large pressure tank, however, is that it cost more than smaller tanks. Large tanks also take up more space than smaller ones and could potentially try to pump water faster than your well can supply it.
To avoid any of these potential issues, you should use the formula and instructions above to choose a well pressure tank that's the perfect size for your home or business.