• The number and size of radiators.

• The available electrical supply.

• Consumer-unit capacity.

• Hot-water requirements.

• The number of bathrooms.

• Available cylinder space.

• Heating controls.

• Electricity tariffs.

• Expected annual running costs.

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APN Boilers helps homeowners find experienced professionals who can assess the heating system, electrical supply and domestic hot-water requirements before recommending an electric boiler.

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What Is an Electric Boiler?

 

An electric boiler uses electrical heating elements to heat water for a wet central-heating system.

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The heated water is circulated through:

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• Conventional radiators.

• Wet underfloor heating.

• Towel radiators.

• Fan convectors.

• A combination of wet heating emitters.

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Energy Saving Trust describes electric boilers as systems that heat water before sending it through radiators or underfloor-heating pipes.

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Some systems also incorporate substantial hot-water storage and are designed to take advantage of cheaper electricity periods.

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An electric boiler is different from:

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• An electric panel heater.

• A storage heater.

• An electric radiator containing its own element.

• Electric underfloor-heating cable.

• An immersion heater.

• A standalone electric water heater.

• A heat pump.

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An electric boiler retains the familiar pipework, radiators and room controls associated with a wet central-heating system.

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Types of Electric Boiler

 

The phrase electric boiler can describe several different arrangements:

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• Electric flow boilers for central heating.

• Electric boilers working with a separate hot-water cylinder.

• Combined electric boiler-and-cylinder units.

• Electric boilers designed for underfloor heating.

• Small electric boilers serving an extension or separate zone.

• Electric hot-water boilers or storage water heaters.

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Understanding the difference is important because central heating and domestic hot water are separate requirements.

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Electric Central Heating Boilers

 

An electric central heating boiler heats water for circulation through a wet heating system.

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It can work with standard radiators, wet underfloor heating, pumps, programmers, room thermostats and thermostatic radiator valves.

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Manufacturer guidance confirms that electric flow boilers can be used with conventional radiators and underfloor-heating systems.

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A central-heating-only electric boiler may not produce water for baths, showers and taps.

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Domestic hot water may instead be provided by:

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• A separate direct electric cylinder.

• An indirect cylinder heated by the boiler.

• An unvented hot-water cylinder.

• A separate point-of-use water heater.

• An immersion heater.

• A combined boiler-and-cylinder package.

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The installer should establish exactly what the selected appliance provides rather than assuming every electric boiler supplies both services.

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Electric Flow Boilers

 

An electric flow boiler heats water as it passes through the appliance and sends that heated water around the central-heating system.

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It can often be connected to an existing wet system where the radiators and pipework remain suitable.

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Electric flow boilers can be appropriate where:

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• A property already has radiators.

• A gas boiler flue cannot be accommodated.

• There is no mains gas connection.

• Fuel storage is impractical.

• The boiler must be installed internally.

• A compact and quiet appliance is required.

• A separate heating zone is being created.

• An extension or loft conversion requires independent heating.

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Some models can work with both sealed and open-vented systems, although this is product-specific and must be confirmed from the manufacturer’s instructions.

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Electric Combi Boilers

 

The phrase electric combi boiler can be misleading because not every electric combi operates like a gas combination boiler.

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A gas combi usually heats domestic hot water instantaneously when a tap is opened. Many electric boilers do not have sufficient electrical output to provide high-flow instantaneous hot water to a whole home in the same way.

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Some products described as electric combi boilers are actually packaged systems containing:

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• An electric flow boiler for central heating.

• A separate stored hot-water cylinder.

• Immersion heaters.

• A circulating pump.

• Expansion equipment.

• Heating and hot-water controls.

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For example, the Electromax system combines an electric flow boiler with an integral 180-litre unvented hot-water cylinder and can provide wet central heating and mains-pressure hot water.

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The boiler and domestic hot-water cylinder may be housed in the same casing, but they can operate as separate systems.

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Homeowners searching for an electric combi boiler should therefore ask:

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• Is hot water instantaneous or stored?

• What is the cylinder capacity?

• How long does the cylinder take to reheat?

• Can heating and hot water operate together?

• How many bathrooms can the system serve?

• Is an off-peak electricity supply recommended?

• What electrical circuits are required?

• Will the unit fit within the available cupboard?

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Is an Electric Combi Boiler Suitable for a Flat?

 

An electric combi boiler can be a practical option for some flats because it does not require a combustion flue or gas supply.

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It may suit a flat where:

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• There is no mains gas.

• The freeholder restricts new gas flues.

• External flue positioning is impossible.

• The property is relatively small.

• Heat loss is limited.

• Hot-water demand is moderate.

• The electrical supply is adequate.

• There is space for any required hot-water storage.

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Leasehold restrictions should still be checked before installation, particularly where work affects common electrical supplies, cupboards, external walls or shared service routes.

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The likely running cost should also be considered. Energy Saving Trust notes that electric heating may be practical in a small or well-insulated flat, but standard-rate electricity remains considerably more expensive per unit than gas.

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Electric Hot Water Boilers

 

The phrase electric hot water boiler can refer to several different products.

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It may mean:

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• An electric central-heating boiler connected to a cylinder.

• A packaged electric boiler-and-cylinder unit.

• A direct electric hot-water cylinder.

• An electric storage water heater.

• A small point-of-use water boiler.

• A commercial drinking-water boiler.

• An instantaneous electric water heater.

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This distinction matters because a product designed to heat water for sinks may not provide central heating, while a central-heating flow boiler may not directly supply baths and showers.

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Electric storage water heaters are available to serve multiple basins or sinks, while combined boiler-and-cylinder systems can provide both central heating and domestic hot water.

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Before choosing an electric hot-water boiler, the installer should assess:

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• The number of occupants.

• Number of bathrooms.

• Bath and shower use.

• Simultaneous outlet demand.

• Incoming water pressure.

• Cylinder capacity.

• Reheat time.

• Available cupboard space.

• Peak and off-peak electricity tariffs.

• Whether central heating is also required.

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Electric Boiler With a Hot-Water Cylinder

 

An electric boiler can work with a separate hot-water cylinder.

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The cylinder may be heated:

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• Directly by immersion heaters.

• Indirectly by water from the electric boiler.

• Using both arrangements.

• Primarily during off-peak electricity periods.

• With a daytime boost facility.

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Stored hot water can provide better performance for homes where several outlets may be used together.

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The cylinder should be sized around:

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• Household occupancy.

• Number of bathrooms.

• Bath sizes.

• Shower flow rates.

• Simultaneous use.

• Reheat time.

• Available off-peak periods.

• Available space.

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An undersized cylinder may run out of hot water, while an unnecessarily large cylinder can increase standing heat losses and installation space.

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Can an Electric Boiler Use Existing Radiators?

 

An electric boiler can often be connected to an existing wet central-heating system.

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Existing components may be retained where they are in suitable condition, including:

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• Radiators.

• Underfloor-heating circuits.

• Heating pipework.

• Thermostatic radiator valves.

• Zone valves.

• Room thermostats.

• Circulation pumps.

• Hot-water cylinders.

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Electric flow boilers are designed to work with standard radiators and conventional wet heating controls.

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However, the system should still be checked for:

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• Incorrectly sized radiators.

• Restricted pipework.

• Sludge and corrosion.

• Poor circulation.

• Leaking valves.

• Inadequate pumps.

• Incorrect expansion arrangements.

• Poor zoning.

• Outdated controls.

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A new electric boiler will not correct every defect in an old heating system.

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Choosing the Correct Electric Boiler Output

 

An electric boiler should be sized using the property’s calculated heating demand rather than the number of bedrooms alone.

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The assessment should consider:

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• Floor area.

• Property construction.

• Wall, roof and floor insulation.

• Window performance.

• Ceiling heights.

• Exposed walls.

• Air leakage.

• Desired internal temperatures.

• Radiator outputs.

• Underfloor-heating requirements.

• Extensions and converted spaces.

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An oversized boiler can create unnecessary electrical demand and may cycle frequently. An undersized boiler may run continuously and struggle to maintain comfortable temperatures during cold weather.

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The heating output and domestic hot-water requirement should be calculated separately.

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A boiler that is adequate for the radiators may not automatically provide the required quantity of domestic hot water.

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Check the Electrical Supply First

 

The electrical installation must be assessed before an electric boiler is ordered.

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Depending on the boiler output and property, the installation may require:

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• One or more dedicated electrical circuits.

• New supply cabling.

• Suitable circuit protection.

• Local isolation switches.

• Consumer-unit alterations.

• Additional RCD or RCBO protection.

• Earthing and bonding checks.

• Confirmation of the incoming supply capacity.

• Coordination with the electricity network operator.

• Consideration of single-phase or three-phase capacity.

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The total electrical demand should include other significant loads such as:

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• Electric showers.

• Immersion heaters.

• Electric ovens.

• Vehicle chargers.

• Electric underfloor heating.

• Hot tubs.

• Battery-storage equipment.

• Other high-demand appliances.

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Manufacturer instructions for combined electric boiler-and-cylinder systems specify permanent electrical connections and separate supplies for different heating elements. The exact arrangements vary by appliance and must be designed by a competent electrician.

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Consumer-Unit and Cable Upgrades

 

An existing consumer unit may not have sufficient spare capacity for a new electric boiler.

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Possible work can include:

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• Installing a new circuit.

• Replacing protective devices.

• Upgrading the consumer unit.

• Installing larger supply cables.

• Providing an isolation switch near the boiler.

• Dividing the boiler and cylinder between circuits.

• Upgrading earthing or bonding.

• Testing the complete installation.

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The quotation should identify whether these costs are included.

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Homeowners should not purchase an electric boiler based solely on its heating output before the electrical supply has been checked.

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Single-Phase and Three-Phase Supplies

 

Many domestic properties have a single-phase electrical supply.

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Some larger electric heating systems may require more electrical capacity than can reasonably be provided through the existing arrangement. In such cases, the installer and electrician may need to investigate:

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• A lower-output boiler.

• Improved insulation to reduce heat demand.

• A staged or load-managed system.

• An alternative heating arrangement.

• A three-phase electricity supply.

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A three-phase upgrade is not available or economical in every location. It should be investigated before the final boiler specification is agreed.

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Benefits of Electric Boilers

 

Electric boilers can provide several practical advantages:

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• No combustion flue.

• No gas connection.

• No oil or LPG storage tank.

• No fuel deliveries.

• Compact appliance sizes.

• Quiet operation.

• Flexible internal positioning.

• Compatibility with wet radiators.

• Compatibility with wet underfloor heating.

• No combustion emissions at the property.

• Fewer combustion-related components.

• Straightforward integration with modern controls.

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They can be particularly valuable where providing a compliant gas or oil flue would be difficult.

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Manufacturer information also identifies compact dimensions, quiet operation and the absence of flue losses as key benefits of electric flow boilers.

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Electric Boiler Efficiency

 

Electric boilers convert electricity into heat at the point of use without losing combustion heat through a flue.

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Some electric-flow-boiler manufacturers publish boiler efficiencies of around 99.8%. This is a measure of the conversion of electricity into useful heat within the appliance and should not be confused with the cost of buying that electricity.

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A highly efficient appliance can still be expensive to operate where its fuel is costly.

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The complete result also depends on:

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• Property heat loss.

• Electricity tariff.

• Heating hours.

• Thermostat settings.

• Radiator sizing.

• System controls.

• Hot-water use.

• Cylinder standing losses.

• Whether off-peak electricity is available.

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Electric Boiler Running Costs

 

Running costs are one of the most important considerations when choosing an electric boiler.

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Energy Saving Trust states that electricity is currently around four times more expensive per unit than gas. It warns that electric heating can therefore be costly, particularly where it is used to heat an entire poorly insulated home.

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The actual cost will depend on:

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• Boiler output.

• Annual heat demand.

• Electricity tariff.

• Peak and off-peak prices.

• Length of heating periods.

• Desired room temperatures.

• Property insulation.

• Hot-water demand.

• Cylinder size.

• Heating controls.

• Solar generation and battery storage.

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The installation price may be lower than some alternatives, but the expected lifetime running cost should also be reviewed.

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Off-Peak Electricity Tariffs

 

Some electric boiler systems are designed to use lower-cost electricity during off-peak periods.

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Energy Saving Trust explains that electric boilers are commonly paired with tariffs such as Economy 10, which provides several periods of lower-priced electricity during the day.

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Combined electric boiler-and-cylinder manufacturer guidance may also recommend heating stored water during off-peak periods and aligning some central-heating use with those tariff windows.

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Before choosing a tariff-controlled system, homeowners should establish:

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• When the reduced-rate periods occur.

• Whether the tariff is available from their supplier.

• The peak-rate electricity price.

• Whether a compatible meter is installed.

• How heating demand fits the tariff windows.

• Whether the property has an RTS meter requiring replacement.

• How daytime boost heating will be charged.

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A tariff that offers cheaper electricity at certain times may charge more at other times, so the complete tariff should be compared.

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Heating Controls

 

Suitable controls can reduce unnecessary electricity use and improve comfort.

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An electric central-heating boiler may work with:

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• Programmable room thermostats.

• Smart thermostats.

• Thermostatic radiator valves.

• Separate heating zones.

• Underfloor-heating controls.

• Cylinder thermostats.

• Hot-water programmers.

• Off-peak tariff controls.

• App-based heating management.

• Load-management controls.

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Energy Saving Trust advises that programmers, thermostats and radiator valves help ensure heating operates only when required.

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The controls should be designed as part of the installation rather than added after the boiler has been selected.

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Electric Boilers for Extensions

 

An electric boiler can sometimes provide a practical independent heating system for:

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• A loft conversion.

• A garage conversion.

• A garden room.

• A self-contained annex.

• A new extension.

• A converted outbuilding.

• A separate floor or apartment.

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This may avoid extending existing gas or oil pipework over a considerable distance.

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However, the additional electrical load and expected running cost must still be assessed. It may be more economical to extend the main central-heating system where adequate boiler and pipework capacity already exists.

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Electric flow-boiler manufacturers identify extensions, loft conversions, conservatories and garages as potential applications where space is limited.

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Electric Boilers for Larger Homes

 

Electric boilers can technically heat larger properties, but the required output may create significant electrical demand and high running costs.

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A larger home should be assessed for:

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• Room-by-room heat loss.

• Existing electrical capacity.

• Three-phase availability.

• Radiator sizes.

• Hot-water storage.

• Available plant space.

• Insulation improvements.

• Electricity tariffs.

• Heat-pump suitability.

• Hybrid heating options.

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In many larger homes, a heat pump, biomass boiler, oil boiler or LPG system may warrant comparison before a direct electric boiler is selected.

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Electric Boiler or Heat Pump?

 

Electric boilers and heat pumps both use electricity, but they operate differently.

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An electric boiler creates heat directly using electrical resistance. A heat pump transfers heat from the outside air or ground into the property.

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Energy Saving Trust explains that a heat pump can typically provide around three units of heat for each unit of electricity used, making it substantially more efficient than direct electric heating.

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A heat-pump installation may require:

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• An external unit.

• A room-by-room heat-loss calculation.

• Larger radiators.

• A hot-water cylinder.

• Pipework alterations.

• Improved insulation.

• Electrical work.

• Different heating controls.

• More installation space and upfront cost.

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An electric boiler may remain suitable where:

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• External heat-pump equipment cannot be accommodated.

• The property is small and well insulated.

• Installation simplicity is important.

• Heat demand is relatively low.

• A wet heating system already exists.

• Leasehold or planning constraints affect external equipment.

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The decision should consider installation cost, running cost, property suitability and long-term use.

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Electric Boiler or Electric Radiators?

 

An electric boiler provides heat through a central wet system. Electric radiators produce heat individually within each room.

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An electric boiler may be preferable where:

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• Existing radiators and pipes can be retained.

• Centralised control is desired.

• Wet underfloor heating is installed.

• A future heat pump may use the same distribution system.

• Stored domestic hot water is required.

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Individual electric radiators may offer:

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• Simpler installation.

• No wet pipework.

• Independent room control.

• Lower risk of water leaks.

• No central boiler.

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Both systems use direct electricity, so the property’s heat demand and electricity tariff remain important.

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System Cleaning and Water Treatment

 

An electric boiler connected to an existing heating system should be protected from contamination.

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The installer should inspect:

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• System-water quality.

• Corrosion.

• Sludge.

• Radiator performance.

• Pump condition.

• Expansion equipment.

• Leaking valves.

• Heating-system pressure.

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Manufacturer instructions may require flushing, cleaning and inhibitor treatment before commissioning.

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The completed installation may also require:

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• Chemical inhibitor.

• A magnetic or system filter.

• Radiator balancing.

• Replacement valves.

• Improved air removal.

• Pressure testing.

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The boiler warranty conditions should be checked before installation.

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Building Regulations and Certification

 

Electric boiler work may involve several areas of Building Regulations compliance.

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Part L covers the energy efficiency of heating and hot-water systems. Current government guidance is contained within Approved Document L, with the applicable edition depending on the building work and transitional arrangements.

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Electrical installation work in dwellings must comply with Part P in England. Approved Document P covers the design, installation, inspection, testing and provision of electrical safety information, including when work must be notified.

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Where a new unvented hot-water cylinder is installed, additional Building Regulations requirements will apply to the cylinder, safety controls and discharge arrangements.

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Homeowners should retain:

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• Electrical installation certificates.

• Building Regulations certificates where applicable.

• Boiler commissioning documents.

• Cylinder commissioning records.

• Manufacturer warranties.

• Control instructions.

• System-treatment records.

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Different regulatory arrangements apply in Scotland, Wales and Northern Ireland, so the installer should follow the requirements applicable to the property.

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What Should an Electric Boiler Quotation Include?

 

A detailed quotation should identify:

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• Boiler manufacturer and model.

• Boiler output.

• Whether it provides heating only.

• How domestic hot water will be supplied.

• Cylinder type and capacity.

• Boiler and cylinder locations.

• Required electrical circuits.

• Consumer-unit alterations.

• Supply-cable requirements.

• Isolation and protection equipment.

• Heating controls.

• Off-peak tariff controls.

• Pipework alterations.

• Pumps and expansion equipment.

• System cleaning and treatment.

• Removal of existing equipment.

• Commissioning.

• Electrical and Building Regulations certification.

• Making good.

• VAT.

• Exclusions and provisional costs.

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The quotation should also state whether the existing electricity supply has been confirmed as adequate.

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Find an Electric Boiler Installer Through APN Boilers

 

APN Boilers brings together experienced heating and electrical professionals serving homeowners across the UK.

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A successful electric boiler installation should provide more than a compact appliance. It should include:

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• A boiler matched to the property’s heat loss.

• An electrical supply capable of supporting the load.

• Correctly sized radiators or underfloor heating.

• A suitable domestic hot-water arrangement.

• Effective heating controls.

• Consideration of electricity tariffs.

• Proper commissioning and certification.

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Whether you are considering an electric central heating boiler, electric combi boiler or electric hot water boiler, the heating system and electrical installation should be assessed before the product is selected.

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Tell APN Boilers about your property, existing heating system, number of bathrooms and available electricity supply. We will help you find an appropriate professional to advise on and install your electric boiler.

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