Do I need an expansion tank for my water heater?

Whether you're looking at ways to improve your water heater or just simply trying to understand the ins and outs of your plumbing a little bit better, it's worth knowing what an expansion tank can do for your heater.

In this blog, we'll delve into whether or not you need an expansion tank for your water heater, what the tank does, how it works, and if it's a necessary addition to your household.

How do water heaters work?

Firstly, it's worth noting that a water heater is different to a boiler, and while they both have similar functions, they are not the same. A water heater in your home will work to heat water for things like cooking and cleaning, whereas a boiler can do this whilst also supplying heat to your home.

So, with a water heater, when cold water enters the bottom of the tank, it gets heated by either electric elements suspended inside the tank or, in more traditional models, a gas flame below it.

Water heaters also have an adjustable thermostat that regulates and maintains the water temperature, depending on the user's needs.

Different types of water heaters

For those more interested in learning about the mechanics of water heaters, there are four main types of water heater:

  • Conventional storage tank water heaters: these work via a large insulated storage tank that holds hot water until it's needed for use.
  • Tankless water heaters: these appliances heat water instantly, upon request without the use of a storage tank. When a hot water tap is turned on, cold water flows through a heat exchanger in the unit and is heated within the boiler.
  • Heat pump water heaters: these water heaters use electricity to move heat from one place to another instead of generating heat directly like a conventional or tankless heater.
  • Solar water heaters: with the help of solar panels, energy is gathered from the sun and transferred as heat to insulate the water heater tank.

There are also variations with water heaters in regards to whether they are vented or unvented. You can read more about what this means and the differences between vented and unvented water heaters on our blog.

Understanding thermal expansion

To understand a little more about the need for expansion tanks, It makes sense for us to go over thermal expansion.

Thermal expansion is essentially the process of water expanding when it is heated, which, as you can imagine, happens in a water heater. Because of this, system designers must include provisions for thermal expansion - this is where thermal expansion tanks come in.

Thermal expansion can be problematic if not managed properly, which is why pressure relief valves are used to ensure safety if expansion levels reach dangerous levels.

The pressure relief valves will often be placed on top of your thermal expansion tank, and you'll know when the pressure inside is too high by the pressure gauge needle.

What is an expansion tank?

So now we’ve learned more about thermal expansion, it’s time to understand how to tackle it. A water heater expansion tank is a small tank that is attached to the water supply pipe of the heater. The expansion tank is designed to handle the thermal expansion of water as it heats up in the water heater, preventing excess water pressure.

Speaking technically, there is a pressurised area within the expansion tank, sometimes called an air bladder. This absorbs the additional water by expanding and contracting, similar to a biological bladder.

So, as the water becomes hotter, it expands and increases the pressure within the tank and plumbing system. The pressure inside these systems is important as it keeps the water inside flowing smoothly and effectively. If it's either too high or too low, you'll run into problems.

Do I need an expansion tank for my water heater?

Alongside the clear benefits listed below, it's worth noting an expansion tank is a requirement for any water heater on a closed plumbing system. New homes are built with a closed water system, so there's a high chance you will need an expansion tank installed.

Every UK home has been built with either a closed or open plumbing system. A closed plumbing system prevents water from flowing in the reverse direction. Put simply, once water enters your home from external pipework, it won't go back into that pipework.

On the other hand, an open system means that water inside the plumbing can be forced back into the mains water through the supply line. These systems do not require an expansion tank.

The benefits of expansion tanks

You'll be happy to know that having an expansion tank installed onto your system comes with a list of worthwhile advantages, potentially saving you valuable time and money in the long run.

  • Extended lifespan: Having an expansion tank has been shown to increase the lifespan of your water heater. During the natural process of water expanding and moving within the system, stress is caused to the tank and other components.
    The expansion tank reduces this strain, in turn preventing any early failure and extending its lifespan.
  • Pressure regulation: Similarly to the above point, when water expands during heating, the expansion creates high pressure within a closed system.
    An expansion tank helps regulate and relieve this pressure, preventing damage to the water heater, pipes, and other components of the plumbing system.
  • Energy efficiency: When there is excess pressure in the water heater system, the relief valve may activate to release the pressure, leading to the loss of valuable heated water and wasted energy! With an expansion tank, the excess pressure is absorbed and stored, reducing how much the pressure release valve activates.
    As a result, less heated water is wasted. This will in turn lead to improved energy efficiency and lower your household energy bills.
  • Maintenance reduction: To expand on the above points, by increasing the overall health of your water heater system, you can naturally expect fewer maintenance issues and plumber call-outs over time, saving you time and money.

Potential issues if you don’t have an expansion tank

Without an expansion tank, you can expect a few issues to crop up in a water heater system, including:

  • Pipe damage: When water heats up and expands, the absence of an expansion tank means there is no designated space for the excess water to go. As a result, the pressure in the system can quickly rise to potentially dangerous levels, causing a strain on your plumbing. The increase in pressure can lead to leaks, breaks, or even a complete system failure.
  • Shortened lifespan of your water heater: perhaps the most important to note is that prolonged periods of high pressure from thermal expansion can significantly reduce the water heater's lifespan.
    The strain on the tank and other components can lead to premature failure, requiring early replacement of the water heater and in turn, some irritating costs.
  • Underperformance: there's a high chance that a water heater may experience avoidable fluctuations in pressure and temperature without an expansion tank.
    This can impact the performance and efficiency of the system, leading to inconsistent hot water supply, longer heating times, and increased energy consumption.

How to check what type of plumbing system you have

Don't worry, whilst we understand that interfering with any appliances that you do not fully understand can seem daunting, there are a few ways you can check whether your system is closed or open.

The determining component to tell if you have a closed plumbing system is the inclusion of backflow prevention devices, also known as pressure-reducing valves. These are often n-shaped pieces of pipework, like this.

In most instances, you can find these in a utility room or outside of your property. If you're unsure, you can always get in touch with a plumber to assess your situation and give recommendations on any next steps.

Can I install an expansion tank myself?

While an unqualified person can technically install an expansion tank on their water heater, it is widely recommended to have a professional plumber or technician handle installations like this.

An expansion tank installation involves working with the water supply and pressure systems, which can be complex and potentially dangerous if not done correctly.

A professional will have the necessary knowledge to install the appliance safely and in compliance with local plumbing codes.

In conclusion, expansion tanks offer several benefits that can't be overlooked in the modern day, especially with increasing costs of living.

The most important perk they bring is their ability to extend the lifespan of your water heater. Alongside this, expansion tanks can reduce noise, improve energy efficiency, and massively extend the lifespan of your system.

Overall, expansion tanks or vessels are a cost-effective and practical solution to ensure a safe and efficient water heater system. Here at Plumbnation, we offer a wide array of plumbing supplies to help get the most out of your home, whether you're looking to make aesthetic or functional improvements.

Frequently asked questions about water heater expansion tanks

Is a large expansion tank better?

As a general rule of thumb with expansion tanks, it is better to oversize than to undersize. Think of it this way, it's much better to have a little too much space spare in the tank rather than the system having to work overtime too often due to not enough space.

How long do expansion tanks last?

Depending on how much it is used, the quality of the tank and the conditions it is installed, the lifespan of an expansion tank can be between 5-10 years.

How much does an expansion tank cost? 

According to Forbes, the price of an expansion tank varies from £70 to £270, depending on brand and supplier. We have a great range of expansion tanks over at Plumbnation.