24kW Electric Boiler

24kW Electric Boiler

24kW Electric boiler from Flexiheat UK

Electric boiler 24kW Output options

A 24kW electric boiler is a highly efficient and cost-effective alternative to oil, solid fuel, natural gas, or LPG boiler systems and even electric storage heating.

They are the ideal alternative for properties without mains gas supply and residences with gas boiler limitations or gas boiler restrictions, such as listed buildings or being sited in a bedroom, etc. An electric boiler can be used for a radiator wet central heating system and is also suitable for hot water underfloor heating systems for medium or small properties.

You will require a three-phase electric supply to be able to run the boiler; they do not make a single phase electric boiler at 24 kW of boiler output.

Our range of electric boilers can also be coupled to an indirect hot water storage cylinder to provide domestic hot water for hot water outlets such as showers, bath taps, or sink taps.

Our 24kW electric system boiler option has all the components required for a sealed heating system, such as an expansion vessel and an ErP-compliant modulating pump.

These boilers are not suitable for open-vented systems.

An eco-friendly heating and hot water solution

When you produce (such as a photovoltaic system, i.e., solar panels) or buy renewable electricity or “green” electricity from renewable sources to run your electric boiler, your electric heating system is carbon neutral and not impacting the environment.

When operating electric boilers, they emit no combustion gases or noxious fumes, unlike traditional gas boilers or oil boilers, as there’s no flue requirement with an electric boiler.

Electric boilers, with easier installation, are a very cost-effective alternative to existing tank-based fuels such as oil or LPG boilers and heat pumps. Air source heat pumps are expensive, and ground source heat pumps even more so, as the installation costs are extreme, to say the least, especially when compared to electric boiler installation costs, even when an upgrade to a three phase electric power supply is required.


  • Compact units compared to typical oil, solid fuel, or gas system boilers
  • No mains gas supply to run to the boiler, only electrical cables.
  • No bulky external tank that you require when heating with oil or LPG systems.
  • Operates quietly—virtually silent
  • No chimney or venting system is needed, making them a perfect solution for listed buildings or medium to small properties that may have gas boiler restrictions.
  • No danger of carbon monoxide poisoning; there is zero risk.
  • Superior inner design that includes a built-in pump for sufficient flow rates for radiators or underfloor heating circuit and an expansion vessel for the heating system
  • Suitable for wet central heating, either radiator or underfloor heating systems
  • Can produce domestic hot water via an indirect hot water cylinder for sufficient flow rates to serve your hot water outlets.
  • Easy-to-use touch screen control panel interface for superior performance
  • Can be used with renewable electricity from renewable sources such as photovoltaic system, wind or water generated electricity etc.
  • Operating temperatures up to 80 °C
  • Running costs are reduced due to the high modulation of the heating system.
  • Electric boilers are a very cost-effective alternative to heat pumps, gas and oil boilers, or electric storage heating.
  • When operating electric boilers emit no harmful gases, fumes, or pollutants.
  • Warranty – 2 years
  • Only suitable for properties with three phase electrical supplies

24kW Electric Combi Boiler

We also offer a 24kW electric combi boiler, a boiler capable of providing space heating and instantaneous domestic hot water. You can find this electric combi boiler range from Flexiheat UK on its dedicated webpage electric combi boiler range from Flexiheat UK. Please note that you will require a three-phase electric power supply to run an effective electric combi boiler. Our 24kW electric combi boiler will produce an instantaneous domestic hot water flow rate of 12.8 litres per minute with a temperature rise of 30 °C (the DHW temperature outputs range are adjustable from 30 °C to 55 °C). This flow rate is sufficient to fill a bath tub in a suitable timescale. They do not make a 24kw electric combi boiler in single phase.

Electric combi boilers really require a 3 phase power supply to produce an adequate domestic hot water flow rate. It’s as simple as that.

24 kW Electric boiler outputs options

The first question is why a 24kW boiler? Well traditionally the smallest gas boilers were 24kW in output and many people assume that this is the smallest boiler available in electric. This is not true, as they go all the way from the smallest output of 0.5 kW all the way up to 45kW for our domestic size electric heating boilers.

So, if you’re replacing a gas or oil boiler that’s 24kW – then the first thing you should do is check that this boiler isn’t oversized for your location – please see this webpage for guidance – What size electric boiler do I need?

We have a couple of options for around 24kW of output – these are

Our Model FHEL23, which is a fully modulating boiler – this unit has a maximum output of 22.5 kW – and will ramp up and down the following outputs to suit the heating demand of the system. Modulation range / power steps = 2.5,5,7.5,10,12.5,15,17.5,20 or 22.5kW


24kw output electric boiler option A from Flexiheat UK

FHEL23 boiler, with low heat output modulation – Output can be set to either – 2.5,5,7.5,10,12.5,15,17.5,20 or 22.5kW


The second option is our FHEL30 unit – this unit’s maximum heating power is 30kW – however this unit can be set to a maximum of 25kW output, so ever slightly over the 24kW, and the unit will ramp up and down this scale to suit the heating demand.

Output can be set to either 5,7.5,10,15,17.5,20,25,27.5 or 30kW

FHEL30 option for an electric boiler output of 25kW:electric boiler specialists installation

Please note – a heating expansion vessel need to be fitted external to the unit for this size boiler to make it a system boiler


The Amps required to power the unit at 25kW output is calculated as follows –

For Three Phase /415 Volt / 50 Hertz AC Circuit, that we use in the UK, then the calculation is –

Amps = (kW × 1,000) ÷ (√3 × volts)

Amps = (25 × 1,000) ÷ (1.73 × 415)

Amps = 25000 ÷ 717.95

Amps = 34.82 Per Phase – on the three phases of the electricity supply

Plus, you want to and the pump electricity requirements of one Amp per phase (3 Amps in total)

Thus, the maximum total electrical consumption would be 35.82 ( call it 36 Amps) per phase

The full brochure on these units is here –

Flexiheat Brochure For Electric Boilers

and the installation and technical manual is here –

Flexiheat Electric Central Heating Boilers – Installation & User Manual – FHEL Boilers


Domestic hot water production

Heating hot water for sanitary use – by using the heating electric boiler in conjunction with an indirect domestic hot water tank, you can supply plentiful amounts of domestic hot water for your bathing needs, be it showering, filling a bath, or washing up in the kitchen.

This hot water system ensures that the electric boiler does both your heating system and domestic hot water—the wet central electric heating system, be it radiators, underfloor heating, or a mixture of both and the domestic hot water via indirect cylinders. We refer to electric boilers in these circumstances as system boilers.

electric boilers for heating and hot water;electric boilers for hot water and central heating; electric hot water boiler system

A diagram showing how an electric central heating boiler is connected to a Domestic Hot Water Cylinder or Hot Water Tank

Control options

Using an appropriate controller on our electric boilers can produce superior performance and lower monthly running costs.

OpenTherm is a communication protocol between heating controls and the boiler to modulate the temperature flow through a heating system.

Since it’s a standard protocol, any “OpenTherm” controller, such as Nest, Hive, Honeywell, Drayton, etc., can work with our electric boilers. There are so many manufacturers now that if the controller says “OpenTherm,” it will work and help reduce running cost.


Contact us

Should you require further assistance or information on the best 24kW electric boiler on the UK market, that we normally have in stock for express delivery or standard delivery then please contact our sales team on 01202 822221 or click here for our email contact form.