Electric tankless water heater range 9kW to 36kW

Electric tankless water heater range – 9kW to 36kW output


Electric tankless water heater range from 9kW to 36kW for on-demand water heating via electrical power - Flexiheat UK

3 phase tankless water heater range from Flexiheat UK


Our Electric tankless water heater range are 100% energy efficient instantaneous water heaters, that provide domestic hot water in a cost effective manner as they heat water only on demand without wasting energy.

Being an electric water heater, they require a three phase electrical supply as you require the Amps to provide hot water at an adequate flow rate for a bath, shower or multiple hot water taps such as kitchen sink taps or bathroom sinks taps in properties or commercial buildings.

Key takeaways

  • The main disadvantage of electric tankless water heaters is that the electrical power ratings set a limit on the hot water flow rate output achievable.
  • This is why generally you require a Three phase electrical supply rather than a single phase electrical supply to power the instant water heater units.
  • Single phase electric can’t supply the Amps (power) required for an electric instantaneous water heater
  • Heating water by providing hot water on demand lowers energy consumption and lower price energy bills for your water heating system.

Tankless water heater electric powered advantages

When opposed to conventional tank-based water heaters, tankless water heaters—also referred to as an on-demand water heater, instant water heaters or instantaneous water heaters or an inline electric water heater—have a number of advantages. Here are a few of the principal benefits:

1. Energy efficiency: The electric element heats only heat water when there is a demand, unlike storage tank-type water heaters that continuously heat and reheat stored water. This on-demand instant hot water heating process can save a significant amount of energy, reducing water heating energy costs by 20-30%.Electric instantaneous water heaters are 100% energy efficient

2. Space-saving: Tankless water heaters are much more compact in size compared to bulky storage hot water tank heaters and are easier to install. This makes them ideal for homes, smaller homes or apartments with limited space, as they can be mounted on a wall or installed in cupboards.

3.No pressure and temperature safety valves or hot water expansion vessels are required to be installed as there’s no hot water storage in the instant water heater appliance – Thus you don’t have to comply with the “G3” unvented water heater regulations that we have in the UK for hot water installation.

3. Unlimited hot water supply / endless hot water: If the capacity of a standard electric storage tank water heater is surpassed, you can run out of hot water if the tank’s capacity is exceeded .In contrast, instantaneous water heaters have an infinite supply of hot water—so long as the demand doesn’t exceed the instant water heaters flow rate capacity.

4. No standby energy losses: Storage tank water heaters constantly lose heat through the tank walls, even when no hot water is being used. Instant hot water heaters eliminate this standby heat loss, further contributing to energy savings and reduce energy bills for your domestic water heating.

5. Lower risk of leaks and floods: Since instant water heaters don’t store large volumes of hot water, they have a lower risk of leaks and flooding compared to electric storage tank hot water heater models, which can cause water damage if they fail.

Electric tankless water heaters, with their energy savings and longer lifespan, can make them a cost-effective option in the long run, especially for businesses or households with high hot water demand or require a unlimited supply of heated water and in areas with high energy costs due to their 100% energy efficiency.

Instantaneous water heaters range

Our electric tankless hot water heaters have four power ratings, or output ranges, in “one” tankless heater unit. Except for the 27kW and 36kW electric instant water heaters which only have one power setting .

I.e. Our 9kW to 15kW electric instant water heater allows users to select power ratings of 9kW, 11kW, 12kW, or 15kW in one model and our 17kW to 24kW instant water heater can be set to 17kW,18kW,21kW or 24kW.

The cold water at the deepest of winter periods is normally 10C temperature , thus the standard temperature rise of 30 °C is required to provide hot water for use in the winter period. This is shown as Δt=30 in the data below – 


Power output of the tankless water heaters9kW to 15kW Output ratings17kW to 24kW Output ratings27kW36kw
Energy efficiency classAAAA
Heat capacity ( power output setting options)9/11/12/15 kW17/18/21/24 kW27 kW36 kW
Power supply – All require a 3 Phase power supply 400V 3N~400V 3N~400V 3N~400V 3N~
Mains water supply pressure (Bar) min – maximum1 to 101 to 101 to 101 to 6
Hot water flow rate at  Δt=30 in litres per minute4.3/5.2/5.8/7.28.1/8.7/10.1/11.61317.3
Rated current (Amps)3 x 13/15.9/17.3/21.73 x 24.6/26/30.3/34.63 x 393 x 52
Dimensions – W x D x H (in mm)245 x 126 x 440245 x 126 x 440245 x 126 x 440315 x 140 x 492

Please note that this range of compact instantaneous water heaters require a minimum flow rate of 2.5 litres per minute to start heating the water. They will not operate if the flow rate is lower than this point.

Our 11kW to 27kW instantaneous water heater models feature a LCD display showing the instant water heaters set temperature 

Digital display on our instantaneous electric water heaters from 9kw to 27kW from Flexiheat UK

The display on our instantaneous water heater from 9kW to 27kW , showing the hot water temperature set on the water heater


These range of instant hot water electric heaters use bare wire heating elements in the heat exchanger which are particularly well-suited for use in hard water areas


Our 36kW instantaneous water heater has a traditional temperature dial and look like this –

36kW electric instant water heater from Flexiheat UK

36 kW Electric tankless water heaters with no standby energy losses

Our 36kw tankless water heater uses copper shielded heating elements within a heat exchanger, this dependable technology ensures long lifespan of operation and resistance to air bubbles and water deterioration.

Full manuals are here for these instant water heaters 

EIWH5 Series Electric instant water heaters manual from 9kw to 27kW – Flexiheat UK

EIWH36 – 36kW Electric instant water heater manual – Flexiheat UK

Instant Water Heater

Whether the instant water heater is supplying fixtures such as shower, bath, sinks or multiple taps, our electrically powered units heat water ‘instantly’ as it flows through the appliance.

They can be installed either as inline electric water heater or in series to provide enough hot water to suit all installation requirements.

Energy efficient Hot Water heating

Being 100% energy efficient, our 3 phase tankless water heater range have accurate temperature control of water flows you can rely on for daily use in business or domestic water heating applications without storage tanks. You get endless hot water for your hot water tap or shower with reduced energy bills.

Contact us

Should you require further assistance, check stock, or get a price on the best electric tankless water heater  product range on the UK market which are 100% energy efficient, then please don’t hesitate to contact our sales team on 01202 822221 or click here for our email contact form.