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Electric Water Heaters: Everything You Need to Know

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Whether you're replacing an ageing immersion tank, kitting out a new extension, or looking for a smarter way to heat water in a commercial space, electric water heaters offer a flexible, efficient and straightforward solution. In this guide we cover everything you need to know — from how they work and the different types available, to the leading brands and how to choose the right system for your needs.

At Alert Electrical we stock a wide range of electric water heating products from the UK's most trusted brands, all at trade-beating prices with free delivery on orders over £100. Read on to find the perfect solution, then shop our full electric water heating range to get the best deal.

An electric water heater uses electrical energy to heat water for domestic or commercial use. Unlike a gas boiler, there's no flue, no gas connection and no combustion involved — which makes electric systems simpler to install, safer to operate and suitable for virtually any property, including off-gas-grid homes, flats, commercial premises and new builds.

 can store hot water in an insulated tank ready for use, or heat water instantaneously on demand. Some models are designed to supply a single point of use — such as one sink or basin — while others can serve an entire property. That range of applications is genuinely wide, which is why electric water heating has seen rapid growth across both the residential and commercial sectors in the UK.

Types of Electric Water Heaters Explained

Understanding the different types of electric water heater is the first step to choosing the right product. Here's a clear breakdown of what's available.



Vented water heaters, sometimes called open-outlet heaters, work by drawing cold water in from the mains and heating it in a small storage tank. Hot water flows out via a special open fitting on top of the unit — because the outlet remains open, pressure cannot build up inside, so no pressure relief valve is needed.

These units are typically compact and are installed directly at the point of use — above or below a sink. They're a popular choice for small offices, cloakrooms, extensions and anywhere that doesn't have easy access to central hot water.

•	Capacities typically range from 5 to 15 litres
•	Available as under-sink (bottom-entry) or over-sink (top-entry) models
•	Simple wiring and plumbing installation
•	Suitable for light to moderate use at a single point of use



Unvented water heaters are connected directly to the mains cold water supply and heat water under pressure. Because the system is pressurised, they deliver a stronger, more consistent flow of water than vented equivalents — making them a better choice for showers, baths or higher-demand applications.

Unvented systems must be fitted with a temperature and pressure relief valve and an expansion vessel to safely manage pressure build-up. Installation must comply with Part G of the Building Regulations and should be carried out by a competent person holding the relevant G3 qualification.

•	Mains-pressure hot water — no header tanks required
•	Capacities from 7 litres (point-of-use) to 300+ litres (whole-property domestic)
•	Suitable for multi-outlet supply in both domestic and commercial settings
•	Requires a G3-qualified installer to comply with Building Regulations Part G



Point-of-use water heaters are compact units positioned right next to where hot water is needed — typically under or above a sink, in a cloakroom, or in a remote room that's not connected to the central hot water circuit. They heat only the water that's needed, so there's very little wasted heat from long pipe runs.

These heaters are ideal for extensions, annexes, offices and commercial washrooms. They can be either vented or unvented and range from 5 to 15 litres in most cases.



Rather than storing hot water in a tank, instantaneous water heaters heat water on demand as it flows through the unit. This means there's no heat loss from stored water and hot water is available within seconds of turning the tap.

Instantaneous models are designed for low-flow applications such as handwash basins — they are not suitable for supplying baths or kitchen sinks, where flow rates are too high. They're very compact and can be installed discreetly under a sink or inside a cupboard, making them ideal for commercial washrooms, offices and staff kitchens.

•	No storage required — heats water as it flows through
•	Very compact and discreet installation
•	Ideal for handwashing in commercial and domestic settings
•	Not suitable for baths or kitchen sink dishwashing — flow rates are too high



5. Unvented Cylinders (Whole-Property Hot Water)

For homes or commercial buildings that need hot water throughout the property, a larger unvented cylinder is the right choice. These are insulated hot water storage vessels connected to the mains supply and heated by one or more immersion heating elements. They can store anywhere from 70 to 300 litres in domestic models (larger capacities are available in commercial ranges), making them ideal for families, houses in multiple occupation (HMOs) and larger premises.

Top-of-the-range models such as the Heatrae Sadia Megaflo Eco deliver mains-pressure hot water with excellent flow rates for powerful showers and fast-filling baths. The Megaflo Eco carries a lifetime warranty on the cylinder for domestic installations — one of the strongest product guarantees in the UK water heating market.


What Are Electric Water Heaters Used For?

Electric water heaters are used across an enormous range of settings. Here are the most common applications:

•	Homes off the gas grid: Ideal for the approximately four million UK homes without access to mains gas
•	Home extensions: For loft conversions and extensions where connecting to the central heating system isn't practical
•	Commercial premises: Offices, shops, restaurants, schools, gyms and care homes that need a reliable hot water supply
•	Outbuildings: Garages, garden offices and outbuildings requiring a standalone hot water solution
•	Holiday and temporary accommodation: Campsite facilities, holiday lets and student accommodation
•	Flats and apartments: Flats and apartments needing mains-pressure performance without gas
•	Remote cloakrooms and washrooms: Adding a dedicated hot water supply without the cost of plumbing in new pipework from the central system


There are many good reasons why electric water heating has become one of the fastest-growing sectors of the UK heating market.



Electric water heaters run entirely from your mains electricity supply. This makes them the go-to solution for properties not connected to the gas grid, as well as any building where running a gas supply would be impractical or prohibitively expensive.



Compared to gas systems, most electric water heaters are significantly simpler and cheaper to install. Point-of-use units in particular can often be fitted by a qualified electrician in a matter of hours. There's no flue to route, no Gas Safe registration needed and no combustion safety checks — just a cold water supply and a mains electrical connection.



Electric water heaters come in a wide range of sizes, from tiny 5-litre under-sink units to large unvented cylinders. Many models are designed to fit neatly under kitchen countertops or inside small cupboards, so there's a solution for even the most space-constrained environment.



Modern electric water heaters are designed to minimise heat loss. Unvented cylinders feature high levels of insulation to keep stored water hot for longer, reducing the energy needed to maintain temperature. Instantaneous and point-of-use heaters avoid the energy waste associated with long hot water pipe runs, meaning you only heat the water you actually use.



Electric water heaters pair well with solar PV panels and home battery storage systems. If you generate your own electricity, surplus power can be used to heat your water — significantly reducing running costs. As the UK grid continues to decarbonise through wind and solar, all-electric water heating also becomes progressively greener over time.



Electric water heaters don't involve combustion, so there's no risk of carbon monoxide leaks. Modern unvented systems incorporate multiple safety features as standard, including thermostatic controls, thermal cut-outs and pressure relief valves. There's no need for annual Gas Safe inspections either.



From small office kitchens to large hospitality venues, electric water heaters can meet commercial hot water demands efficiently. Many commercial-grade models are built specifically for continuous, high-demand use — with fast recovery times and robust construction to ensure long-term reliability.

Leading Electric Water Heating Brands at Alert Electrical

Alert Electrical stocks products from the most respected names in the UK electric water heating market. Here's a closer look at some of these brands and what they offer.



Hyco is a West Yorkshire-based specialist manufacturer with over 25 years of experience in electric water heating equipment. Their range is particularly well regarded for domestic and light commercial applications, combining reliability with excellent value for money.





•	Speedflow — a versatile range of vented and unvented water heaters available in 5, 10 and 15-litre models, with 1kW and 3kW output options. Suitable for over-sink or under-sink installation in offices, cloakrooms and domestic extensions.
•	Powerflow — a wall-mounted unvented electric water heater designed to provide continuous hot water on a large scale. Suitable for bathrooms, cloakrooms and commercial kitchens, and able to supply 30 to 100 litres of hot water.
•	Rho — a compact instantaneous inline heater designed for point-of-use handwashing. Thermostatically controlled for precise temperature management. Can be installed discreetly under a sink or inside a cupboard.
•	Aquila — an instantaneous inline water heater suitable for handwashing at up to two basins, or dishwashing at one sink.
•	Handyflow — a lightweight over-sink or under-sink heater designed for occasional light use in portable buildings or temporary installations.



deXpro is a fast-growing manufacturer specialising in electric water heating, space heating, and hand drying solutions. Known for combining modern design with strong value, deXpro offers a range of compact and efficient products ideal for domestic and light commercial use. 

On our website, you’ll find popular options such as inline water heaters, digital unvented units, and point-of-use systems designed for quick installation and reliable performance.



Stiebel Eltron is a premium German brand with over 95 years of expertise in electric heating and hot water technology. Renowned for innovation, efficiency, and sustainability, Stiebel Eltron products are engineered for high performance and long-term reliability. 

Our range includes instantaneous (tankless) water heaters, under-sink and over-sink units, and advanced models like the DEM, DCE, and DHB-E series, offering precise temperature control and energy-efficient hot water on demand.


How to Choose the Right Electric Water Heater

With so many products available, choosing the right electric water heater can seem daunting. These five questions will help you narrow it down quickly.



Think about the number of people or outlets being served, and how often hot water is needed. A 5 to 10-litre point-of-use heater is fine for a single handwash basin in a cloakroom. A busy household needs a larger unvented cylinder — typically 150 litres or more. A commercial kitchen or gym changing room may need a high-capacity unit with a fast recovery time.



2. Do you need mains-pressure performance?

If you want powerful showers and fast-filling baths, you need an unvented system. If you're supplying a single handwash basin with occasional use, a vented heater will do the job perfectly well at a lower cost and with simpler installation.



Consider the available space and the proximity to the point of use. A compact under-sink unit is ideal for remote rooms or cloakrooms; a cylinder in an airing cupboard suits whole-property supply. Think also about the electrical supply — larger units require a dedicated circuit, which may need to be installed by a qualified electrician.



For commercial applications, consider models with higher-temperature storage and built-in thermostatic blending valves to comply with Legionella risk assessment guidance. Santon's Aqualine range is specifically designed with this in mind, incorporating a TMV2 valve as standard.



Vented point-of-use heaters start from well under £100, making them extremely cost-effective for simple applications. Unvented cylinders represent a higher upfront investment but deliver superior performance and long-term energy savings. The Heatrae Sadia Megaflo Eco carries a lifetime cylinder warranty for domestic installations — outstanding long-term value for a whole-property solution.

Installation requirements vary depending on the type of system chosen. Here's a summary of the key points.

•	Vented heaters: Most vented point-of-use heaters are relatively straightforward to fit, requiring a cold water supply, an electrical connection and a suitable mounting position. Many are installed by a qualified electrician without the need for a specialist plumber.
•	Unvented systems: Unvented water heaters and cylinders must be installed in accordance with Part G of the Building Regulations. The work must be carried out by a competent person holding a G3 unvented cylinder qualification — usually a qualified plumber. Safety devices including a pressure relief valve and expansion vessel must be correctly installed and commissioned.
•	Electrical wiring: All electric water heaters must be wired in accordance with the current edition of BS 7671 (the IET Wiring Regulations). Larger units typically require a dedicated circuit. Always use a qualified, registered electrician for all electrical connections.

If you're unsure about the installation requirements for a specific product, the Alert Electrical team is happy to advise. Give us a call on 03339 969999.


Are electric water heaters expensive to run?

Running costs depend on the size of the unit, how much hot water you use and your electricity tariff. Modern electric water heaters are highly efficient — insulated storage cylinders retain heat well over time, and instantaneous heaters only use energy when hot water is actually drawn. Using an Economy 7 or time-of-use tariff to heat stored water overnight can reduce running costs significantly. If you have solar PV panels, directing surplus generation to your water heater can reduce bills further.



Can an electric water heater replace a gas boiler?

Yes — for properties that are off the gas grid, an all-electric solution can fully replace a gas boiler setup. The Heatrae Sadia Electromax, for example, combines an electric flow boiler with a 180-litre unvented hot water cylinder to provide both central heating and domestic hot water from a single compact unit. Many homeowners are also making this switch as part of a broader move to all-electric living, particularly when installing heat pumps or solar PV systems.



What's the difference between a vented and an unvented water heater?

A vented water heater has an open outlet — water expands and any excess drips from the open spout, so no pressure builds up inside the unit. An unvented water heater is a sealed, pressurised system connected directly to the mains cold water supply, which delivers water at mains pressure. Unvented systems give stronger water flow but require a more complex, regulated installation including safety valves and an expansion vessel.



How long does an electric water heater last?

Most quality electric water heaters will last between 10 and 20 years with proper maintenance. The Heatrae Sadia Megaflo Eco comes with a lifetime warranty on the cylinder for domestic installations (subject to correct installation, registration within 60 days of purchase, and regular maintenance by a competent person). Immersion elements and thermostats can be replaced if needed without having to replace the whole unit.



Do I need a plumber or an electrician to install an electric water heater?

For most vented point-of-use heaters, a qualified electrician can handle the complete installation. For unvented cylinders and larger storage systems, you'll need both a G3-qualified plumber (to install and commission the plumbing and safety devices in compliance with Building Regulations Part G) and a qualified electrician (to make the electrical connections in compliance with BS 7671). Always ensure all work is properly certified.



Can I install an electric water heater in a bathroom?

Yes, but the unit must be appropriate for the bathroom zone in which it will be installed, and must carry the required IP (ingress protection) rating for that zone. Always refer to the manufacturer's specifications and ensure the installation is carried out by a qualified electrician who is familiar with bathroom electrical zone regulations under BS 7671 and Part P of the Building Regulations.

What size electric water heater do I need?

For a single handwash basin with occasional use, 5 to 10 litres is typically sufficient. For a small family bathroom, 80 to 150 litres is generally recommended. For whole-property supply for 3 to 5 people, 150 to 250 litres is more appropriate. For commercial or high-demand premises, seek advice on peak demand and consider specialist commercial ranges such as the Hyco Powerflow or the Heatrae Sadia Megaflo Commercial range.

Yes — electric water heaters are designed with multiple safety features as standard, including thermostats, thermal cut-outs and (in unvented systems) pressure and temperature relief valves. Because there's no combustion, there is no risk of carbon monoxide leaks and no requirement for annual Gas Safe inspections. Always purchase from a reputable manufacturer and ensure professional installation in compliance with current Building Regulations.

What is a G3 qualification and why does it matter for unvented systems?

G3 refers to Part G, Section 3 of the UK Building Regulations, which governs the installation of unvented hot water storage systems. An installer who is G3 qualified has been assessed as competent to design, install and commission unvented systems safely. Using a G3-qualified installer is a legal requirement for unvented cylinder installations in the UK — not doing so is a breach of Building Regulations and will affect your insurance and the validity of any product warranty.

Why Buy Your Electric Water Heater from Alert Electrical?

Alert Electrical is a UK-based electrical wholesaler trusted by trade professionals and homeowners alike. Here's why so many customers choose us for electric water heating:

•	

 We stock electric water heating products from the UK's leading manufacturers including Heatrae Sadia (Megaflo, Streamline, Hotflo, Electromax, Amptec, PremierPlus), Redring (Powerstream, Reditap), Hyco (Speedflow, Powerflow, Rho) and Santon (Aqualine, Aquaheat)
•	

 Free delivery on all orders over £100 — saving you money from the moment you order
•	

 We offer trade-competitive pricing with a Price Match Promise — if you find it cheaper elsewhere, let us know
•	

 Our expert team is on hand to answer technical questions and help you choose the right product — call us on 03339 969999
•	

 Clear returns policy and dedicated customer care, so your purchase is protected
•	

 We also stock a full range of accessories, controls and electrical equipment so you can complete your installation in a single order

Ready to Find Your Perfect Electric Water Heater?

Whether you need a compact under-sink heater for an office cloakroom, a powerful unvented cylinder for a growing family, or a commercial-grade solution for a busy hospitality venue — Alert Electrical has the product and the expertise to help you get it right.

, including all the leading brands at the best prices. With free delivery on orders over £100 and a team of experts ready to help, there's never been a better time to make the switch to efficient electric water heating.

Electric Water Heaters: Everything You Need to Know

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