The Different Types of Water Heaters

Undersink water heaters are a perfect space-saving solution for homes and workplaces where room is limited. These compact units fit neatly beneath sinks, making them ideal for areas with limited wall space or where a discreet installation is preferred. Commonly referred to as point of use water heaters, they’re ideal for small kitchens, bathrooms, or office kitchenettes, providing hot water exactly when and where you need it.

These water heaters come in two main types: storage models that hold between 5 to 30 litres of water, and instant models that heat water on demand. Instant options are usually more compact and are ideal for settings with very tight space constraints. Many under sink units include temperature adjustment features, allowing you to easily control water heat levels for comfort and safety.

While under sink water heaters are incredibly convenient and easy to integrate into modern kitchen systems, they do have some limitations. They’re generally less energy-efficient than larger, centralized water heating systems. However, they often don’t require an expansion vessel, making installation more straightforward in many cases.

Oversink water heaters are a practical and economical solution for small spaces, where hot water is needed quickly and efficiently. Designed to be installed directly above a tap, they’re ideal for handwashing stations in understairs toilets, utility rooms, or even caravans. These units are commonly used in locations with limited cupboard space, making them a better option than under sink heaters when storage might be tight.

They operate by heating water instantly as it flows through the unit, meaning there’s no need for a storage tank or expansion vessel. This continuous supply system is perfect for situations where hot water demand is low but frequent, like washing hands or rinsing dishes. Some models even come with an integrated tap, providing a convenient all-in-one solution.

Because oversink water heaters only use energy when hot water is needed, they can be more economical than storage-based options. They’re also extremely easy to install, making them a popular choice for DIY enthusiasts and for those wanting a quick upgrade. With no need for a hot water cylinder or complex plumbing, they’re especially well-suited to remote or secondary water points.

Instant water heaters, also known as tankless or on-demand water heaters, provide hot water exactly when you need it, without storing any in a tank. These units are designed to heat water as it flows through the system, eliminating standby energy loss and offering a more efficient alternative to traditional storage water heaters. They’re perfect for those of you who are more energy-conscious or if you have minimal hot water needs.

Many instant water heaters are compact enough to be installed discreetly under a sink, but wall-mounted and oversink versions are also available. Wall-mounted models can be slightly larger to meet higher demand but still offer the same core benefit—hot water on tap, without storage. With no tank to refill, there's no risk of running out of hot water, making them ideal for steady, low-volume use.

Although they offer great efficiency, instant heaters can come with a higher upfront cost and sometimes deliver limited flow rates, which may cause temperature fluctuations if demand exceeds capacity. Despite this, they remain a popular choice for homes, workspaces, and caravans looking for a continuous yet compact water heating solution.