A Complete Guide on How to Size a Well Pressure Tank

A pressurized tank is an important element of well maintenance. By limiting fast on/off cycles of the pumps and sustaining water pressure around your home, pressurized well tanks improve the longevity of your good pump. 

Then, knowing how to size a well pressure tank is essential to guarantee your home water demands fulfillment and protection against short-cycling problems. 

This post will dig deeper into this topic. Follow us to learn more!

How to Size A Well Pressure Tank?


You’ll need to understand three factors to measure your well pressure tank correctly:

Flow Rate

The flow rate of your pump is the number of gallons/ minute it generates.

Minimal Runtime

To calculate the drawdown capacity, multiplying the water flow velocity by the pump’s minimal duration. According to the minimal runtime general rule, any pump running at 10 gallons per minute (GPM) or less ought to generate one gallon per minute of runtime.

For instance, a 10 GPM flow rate multiplied by 1 equals a 10-gallon drawdown capacity. So, everything over 10 GPM should have a runtime of 1.5 GPM.

Or, a 16 GPM flow rate multiplied by 1.5 equals a 24-gallon drawdown volume. Suppose your flow level is greater than 20; you may need more than one tank.

How to Size a Well Pressure Tank

Well Pressure Tank Used To Stabilize Water Pumps

Pressure Switch Setting

The pressure-switch option determines the pressure level at which the pumps start to fill up the tank and turn off after the full container. Compression tanks have three pressure switching options: 20/40, 30/50, and 40/60. 

The first value refers to the pressure level your pump comes back on, while the second figure represents the pressure where it switches off ( 30 psi on, 50 psi off).

The value that disables the pump pressure will have a direct impact on your drawdown capability. Suppose you have a 30/50 switch; for instance, you may have less drawdown ability than when you had a 20/40 switch.

Most well pressure tank producers will give you a graphic showing which your drawdown capability depends on the pressure switch settings.


The following formula may be used to calculate the amount of drawdown required based on the above factors:

Tank drawdown capacity needed = Pump flow speed x running time

The pressure container’s minimal quantity of water held and supplied during pumping close-off and pumping restart is known as tank drawdown capability. This term is not the same as “tank volume.”

For instance, based on the on/off position of the pressure switch, a tank with a volume of 20 gallons only possesses six to seven gallons drawdown capacity. 

Pumps with a fluid velocity greater than 10 gallons per minute should work with a tank with a minimal drawdown capacity of 1.5 gallons per GPM supplied.


Before measuring a pressure tank, consider these parameters as a general guideline:

  1. 0 to 10 gallons per minute: 1 gallon of drawdown/ 1 gallon per minute supplied.
  2. 10 to 20 gallons per minute: 1.5 gallons of drawdown/ 1 gallon per minute supplied.
  3. 20 GPM: 2 gallons of drawdown/ 1 gallon per minute supplied

The proportion of water lost in the tank when the pipework “draws” off this locked pressure is known as drawdown. Simply put, the function of a pressure tank is to keep compression in a plumbing system constant while allowing the pump to rest. 

This eliminates the requirement for the pump to work continuously to maintain system pressure. Although a pressure tank may seem expensive at first, it will save you money over the long term.

A Well Pressure Tank Worth Investment

      A Well Pressure Tank Worth Investment

Pumps that run for a shorter period require minimal maintenance and less energy, leading to less cost. Pressure tanks come in various configurations, the most popular of which are lateral, linear, and vertical. Guarantee to figure out which configuration best suits your plumbing system.

Once you have figured out the flow rate in GPM, established the cut-in/cut-out pressure, and validated our desired run time. You have to choose what cut-in/cut-out pressure you wish to configure the system at.

What To Think About Before Sizing a Well Pressure Tank?

If you are thinking of purchasing a water tank for your house, there are some things you will need to look at first.

How Big Should My Water Tank Be?

A four-person household uses around 700 liters per day or 150 to 200 liters per member.

However, the amount of water tank you require will link to how you want to use the water in your tank. It may come as a shock to learn that the large percentage of the water used in your home is usually spent outdoors, in your bathroom, restroom, or washing.

As a result, if your family uses a lot of water in these areas, a big water tank is not a bad choice.

  High Water Usage Mainly Falls On Bathroom, Restroom, and Outdoors

  High Water Usage Mainly Falls On Bathroom, Restroom, and Outdoors

How Much Will It Cost?

Depending on the size of the tank, the cost might fluctuate since the bigger the water tank is, the more expensive it is. 

Most of the time, the cost is attributable to the tank size and the tank materials. So, a steel tank is more costly than a poly one. Normally, you have to spend roughly from 1000 dollars to 4000 dollars for a home-use water tank. 

How Much Will I Save?

Water costs $2.000 per kL on average, plus around $2 per kL for sewage treatment; you would save a thousand dollars per year in offsetting costs.

This may appear to be little cost savings compared to a big capital expenditure of ten to twelve thousand dollars. Still, in locations where network water is not available, the cost of linking the house to your local utility system water supply may mount up to thousands of dollars.

What Is The Connection Between Pressure and Tank Size?

How Is Tank Size And Pressure Related?

One thing to keep in mind is that the higher the working pressure, the bigger the tank should be. Pressure & tank capacity are inextricably linked; when one rises, the other does too. The greater the pressure level, the less drain there is, necessitating a bigger tank capacity.

A Bigger The Tank Is, The Higher Working Pressure Is

    A Bigger The Tank Is, The Higher Working Pressure Is

Another crucial aspect of any water plumbing system is the pressure levels. 20/40, 30/50, 40/60, and 50/70 are by far the most frequent pressure ratios. 

The majority of producers will provide a pressure tank measurement guide that will allow users to rapidly estimate a tank’s drawdown depending on the pressure levels on the system.

Does A Bigger Pressure Tank Increase Water Pressure? 

A bigger water pressure tank allows you to operate a plumbing item for longer with well pumping “on” phases, which implies that if your pressure typically fluctuates between 20 and 40, it would drop from 40 to 20 slower.

How Setting Up The Pump Pressure Control Switch Better Water Pressure?

To some extent, you can increase the pressure on the pumping control to enhance the water flow rate.

Lookout: When the control is put excessively high, the pump will not meet the cutoff temperature, and it will heat up. Or suppose you install a somewhat stronger pump and raise the pressure much higher than 80 psi; you threaten plumbing leakage.

When the well circulation rate is slow or lacks water, pump protective technology may restrict or stop the flow of fluid via the network until the well recovers.

Similarly, holding additional water in a different water tank lets your pump gently refill the tank without draining the well. In contrast, the water in the container may satisfy spikes in water requirements.

Can I Oversize A Well Pressure Tank?

The pumping cycles will be prolonged (slower) with a bigger tank, but the total duration will stay the same (you utilize 600 gallons of water, the pump needs to deal with 600 gallons of water). For instance, suppose the tank is full, and you turn on a tap. In that case, a 36-gallon tank can take 1 minute for the pump to activate, followed by a half minute to run.

It could take up to over a minute for a 55-gallon pump to operate, after which it will operate for 50 seconds. Assuming you keep the tap running for 10 mins, you’ll receive a total of around 200 seconds or 3.33 minutes of runtime.

The disadvantages of a bigger tank are that it is more expensive and requires more room. The only major issue is that the pump will operate too aggressively if your tank is not big enough, wearing it out sooner. It would be best if the size of your well-pump corresponds to the “make-up”-the flowing rate that water gets back into the well.

The Final Verdict

Hopefully, this article has provided you with useful information on how to size a well pressure tank. 

Bear in mind that there are three important factors to size the well pressure tank. Once you have determined these three factors, apply the formula to find the desired tank capacity.

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