commercial electric water heaters from Flexiheat UK: industrial electric water heatersFlexiheat UK

Commercial Electric Water Heaters

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Commercial & Industrial electric water heaters from Flexiheat UK

Commercial electric water heaters are often used when other fuels such as gas or oil are not available, or when installation requirements make them the best option as commercial electric hot water heater have no flue pipe requirements, or combustion air requirements which gas or oil water heaters have. This makes the installation of an electric commercial water heater easier and often cheaper too.

Commercial electric water heaters are highly energy efficient, at 100%

When the electrical energy powering the calorifiers is generated from renewable sources, then you can also achieve a carbon neutral hot water system, as opposed to gas or oil water heating which impacts the environment, through global warming.

Here at Flexiheat UK, we offer a full range of commercial and industrial electric water heaters, with a product range that features a tank capacity from 80 litres to 3000 litres, which have compact dimensions, and have some high-power output capabilities. These factors make our direct electric water heaters suitable from many heavy domestic as well as commercial and industrial hot water heating applications, serving everything from offices, restaurants, gyms, changing rooms, hotels, and sports or leisure centres to name but a few applications for these commercial electric storage water heaters.

These electric water heaters or electric calorifiers are often used in providing hot water for all types of large commercial and industrial applications, such as hotels, medical centres, hospitals or for large process potable hot water requirements, such as restaurants, factories or locations with large DHW (Domestic Hot Water) requirements.

This range of electric water heaters are rated for a maximum working pressure of up to 8 bar (some are 6 Bar rated) and a water temperature of 5 Degrees C to 90 Degrees C, and can be used as an unvented electric water heater, when fitted with an unvented kit, allowing a pressurised hot water system, fed directly from the mains cold water system, and thus delivering hot water at mains water pressure, which saves energy and expense on purchasing and running hot water pumps.

Duplex stainless-steel construction ensures these electric water heaters are exceptionally resistant to corrosion. Duplex stainless steel is resistant to corrosive water containing up to 2,000 mg of chlorides per litre and resists corrosion in the most aggressive water conditions, giving our commercial electric water heaters an exceptional product lifetime with minimal maintenance. This is why we offer a 10 year warranty on the tank of the water heater, and 2 years on the electrical components.

Immersion heaters

Incoloy immersion heaters are used in hard water areas, while titanium immersion heaters are employed in areas with extremely hard or aggressive water (where high levels of chlorides may be present)

Copper immersion heaters cannot be used in stainless steel cylinders; consequently, you must use Incoloy or titanium, for unvented cylinders or thermal store units.

For this reason, we use the titanium immersion heaters in our electric hot water system for commercial and industrial applications, as they are the best of the best, and we give highest priority to the life expectancy for all our valued customers (all but the 18kW immersion heater which is only available in Incoloy at present)

All electric immersion heaters are 100% energy efficient –

The standard control temperature range is up to 80C, with a safety limit temperature of up to 96°C (both adjustable) for the immersion heaters that we use in our storage water heaters.

So even though the duplex stainless steel hot water tanks are rated up to 90 Degrees C, as standard the complete electric heating hot water system, is suitable for hot water temperatures up to 80C.

For heating hot water for large commercial or industrial applications, which may require temperatures above 80C, we have available options for higher temperature immersion heaters- but please consult us regarding your temperature requirements.

Electric commercial water heaters

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Electric Commercial Water Heater from Flexiheat UK – no heating elements shown for clarity

Just to clarify what the difference between commercial electric water heaters and commercial electric boilers is – a commercial electric water heater uses electric heating elements to heat cold water up the desired temperature for domestic hot water purposes – this is often called “ potable water quality” and is used as the hot water supply for sanitation and personal hygiene, food preparation, washing dishes, clothes washing etc. Whereby a commercial electric boiler is a closed loop heating system and are designed to supply heating hot water, at higher temperatures such as 80 Degrees C or similar to supply a wet heating system that uses heat emitters such as radiators or underfloor heating system to heat the building or space. This heating water is supplied via a pumped pipe system, that cycles the water around the heating system, and then back into the boiler. Thus, this is often called a closed loop heating system. We also do commercial electric boilers, should you require these and they can be found on our dedicated webpage here

Commercial electric water heater sizing

A correctly-sized electric commercial water heater is vital for many businesses including hotels, restaurants or other public premises such as health centres or hospitals. An electric water heater that is too small won’t be able to deliver enough hot water during periods of peak demand, thus sizing the water heater correctly is imperative.

There are 3 components to sizing your commercial electric water heater. They are –

  1. The volume of hot water that you require – How many litres of hot water do you require?
  2. The temperature rise that you want that water to go through e.g. from the incoming water temperature of 10 degrees C to 60 degrees C – 60°C is the minimum recommended water temperature as it reduces Legionella risk.
  3. Lastly your time requirements – how quickly do you want that water to heat up in, or how many litres you require of water per hour.

The following formula is used to calculate the kilowatt (kW) power output required for your commercial or industrial electric hot water heater to heat a specific volume of water by a given temperature rise in one hour.

Volume of water in litres x 4.2 x the temperature rise in degrees centigrade divided by 3600

(just for note – 4.2 being a factor and 3600 being a given constant)


Pt = (4.2 x L x T) / 3600.

Pt is the power, measured in kWh, that was required to heat the water. The amount of water, in litres, that is being heated is denoted by “L,” and the difference in temperature, in degrees Celsius, between the original temperature and the new temperature is denoted by “T.”

Thus, for a 500 litre electric water heater, the calculation would be as follows –

500 litres of water, to be heated from 10°C to 60°C, giving a temperature rise of 50 °C would result in-

500 x 4.2 x 50 / 3600 = 29.16 kW per hour

This means that the 500 litres of water would be heated in one hour by 29.16 kW of applied heat, for the temperature rise of 50°C

We can use this result to conclude other factors or variables – e.g. to heat the same water volume of 500 litres in half the time (i.e. 30 minutes) we would need twice the heating power i.e.  58.33 kW. If we had only half the heating power required i.e. 14.58 kW then it will take twice as long to heat the 500 litres to the required temperature, that being two hours. Lastly, if this commercial electric water heater only had 8kW of heating power then the heat up time would be in excess of three hours.


How to calculate the AMPs required to power our commercial electric water heater-

This will depend on whether your using 1 Phase / 240 Volt supply the maximum immersion heater size we can do running off a 1 phase supply is 6kW, all the rest of the immersion heaters will require a 3 Phase / 415 Volt supply. All of these calculations assume a power factor of 1.

For Single phase – the calculation is as follows –

Amps = (kW × 1,000) ÷ volts

Thus, for a 3kW immersion heater fitted to one of our commercial electric water heaters, the calculation is as follows –

Amps = (3 × 1,000) ÷ 240

Amps = 3000 ÷ 240

Amps = 12.5

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)

Again, based on a 3 kW immersion heater

Amps = (3 × 1,000) ÷ (1.73 × 415)

Amps = 3000 ÷ 717.95

Amps = 4.178 Per Phase

Industrial water heater electric

At what point does a commercial electric hot water heater become an industrial electric hot water heater? well there is no set point with regards to its volume in litres or in kilowatt output, some might say that a  100 litre electric water heater is regarded as a domestic size, and that 500 litre electric water heater is an industrial electric water heater, whilst other may say that a 500 litre is a large capacity electric water heater, or a commercial water heater, it really is in the “words of the beholder” as they say. It’s really up to you what you want to call them, but in reality, they are direct electrically powered storage water heaters, that heat the water by electric heating elements, that produce clean potable domestic hot water, in relatively compact dimensions.

Commercial Water Heater Product information

Our main range in our commercial electric water heater offering is our series 20 units. These electric water heaters are manufactured from Duplex 2205 Stainless Steel, which is the best grade of stainless steel to manufacture commercial electrical water heaters from. This Duplex 2205 Stainless Steel has been developed to improve on the technical weaknesses of stainless steel usually used on hot water heaters and cylinders. It combines the best properties of 2 families of stainless steel: Austenitic (40%) and Ferritic (60%)

Features and benefits of this stainless steel when used in DHW tanks are-

  • Resistance to stress corrosion cracking
  • High chloride resistance
  • High resistance to abrasion
  • High resistance against corrosion
  • Excellent weldability
  • High Mechanical strength

and the most important factor –Does not require an additional protection such as sacrificial anodes to protect the electric water heater, like glass lined water heaters do. 

Many hot water tanks and calorifiers are constructed in steel with a glass lining. The glass lining prevents the hot water contacting the metal and protects it from corrosion to a degree. However, the glass lining is not enough alone to ensure protection, and most glass lined water heaters and calorifiers will be provided with sacrificial anodes as standard items.

Sacrificial anodes often don’t work in soft water areas, such as Scotland, west Wales, south west and north west England, due to the low electrical conductivity of the water, and for this reason our stainless steel electric water heaters are often used in these areas , as they require no anode protection and are not susceptible to corrosion , like glassed lined electric water heaters are.

For more detail on the benefits and features of duplex stainless steel for electric commercial water heaters and tanks, please see the following pdf on the subject –

Benefit and features of duplex stainless steel for electric water heaters commercial – Flexiheat UK

Electric water heaters commercial and industrial

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Electric water heaters commercial from Flexiheat UK – pictured is our 500 litre electric water heater model

The Energy Related Products Directive (ErP), covers all domestic and commercial heating and hot water products, up to 400 kw and 2,000 Litres. Our electric commercial water heater can be supplied with the standard Energy Related Products Directive (ErP)energy rating of “C” or are also available with the energy rating of “A” as an option.These electric water heaters are supplies as standard for floor mounting. Although the 80 litres to 200 litre units can be mounted horizontally, if so required, with the use of an optional horizontal mounting bracket kit.

Below you can see the various options that we have for our commercial water heaters electrically powered. These water heaters can be supplied with various amounts of tapping’s that take an electric immersion heater or heaters depending on the size of the tank. We can fit various combinations of immersion heater power to suit you hot water requirements, as you can see from the following table. For example –

If you require a 500 Litre electric water heater, with 24 kW of heating power, then we can either have two tapping’s, each fitted with a 12kW immersion element, or we could do 4 tapping’s each fitted with 6kW immersion heaters, again giving you 24kW, the choice is yours. The benefit of using more tapping’s, and thus smaller output immersion heaters is closer temperature control and lower electricity draw, as the water heater gets up towards the desired temperature.

This range of commercial and industrial electric water heaters are rated for a maximum working pressure of 6 bar and a water temperature of up to 90 Degrees C for our 80 to 500 litre range, while our water heaters from 740 Litre plus are 8 bar and a water temperature of up to 90 Degrees C. We can, as an option quote both these ranges with a working pressure of 10 Bar if required.

Firstly our 80 Litre to 500 Litre commercial electric hot water heater range


Electric commercial water heater capacityMaximum number of tapping’sElectrical heating elements compatibleMaximum installed power
80 Litre electric water heater11.5kW, 3kW,9kW,12kW12 kW
130 Litre electric water heater11.5kW, 3kW,9kW,12kW12 kW
150 Litre electric water heater23kW, 6kW, 9kW, 12kW24 kW
215 Litre electric water heater23kW, 6kW, 9kW, 12kW24 kW
255 Litre electric water heater23kW, 6kW, 9kW, 12kW24 kW
305 Litre electric water heater33kW, 6kW, 9kW, 12kW36 kW
400 Litre electric water heater33kW, 6kW, 9kW, 12kW36 kW
500 Litre electric water heater53kW, 6kW, 9kW, 12kW60 kW

Download the Flexiheat Commercial Electric Water Heaters Technical Information up to 500L

Then our 740 Litre to 3,000 Litre Industrial electric hot water heater range – these are our Series 20 range

Electric commercial water heater sizeMaximum number of tapping’selectrical heating elements compatible Maximum installed power
740 Litre electric water heater53kW, 6kW, 9kW, 12kW, 18kW72 kW
840 Litre electric water heater **53kW, 6kW, 9kW, 12kW, 18kW72 kW
965 Litre electric water heater **63kW, 6kW, 9kW, 12kW, 18kW108 kW
1000 Litre electric water heater63kW, 6kW, 9kW, 12kW, 18kW108 kW
1380  Litre electric water heater **63kW, 6kW, 9kW, 12kW, 18kW108 kW
1500 Litre electric water heater63kW, 6kW, 9kW, 12kW, 18kW108 kW
1875 Litre electric water heater **73kW, 6kW, 9kW, 12kW, 18kW126 kW
2000 Litre electric water heater73kW, 6kW, 9kW, 12kW, 18kW126 kW
2155  Litre electric water heater **73kW, 6kW, 9kW, 12kW, 18kW126 kW
2500 Litre electric water heater73kW, 6kW, 9kW, 12kW, 18kW126 kW
3000 Litre electric water heater83kW, 6kW, 9kW, 12kW, 18kW138 kW

** NEW for 2022 – these units are not in the following brochure – please contact us for individual drawings for these capacities water heaters.

Download the Flexiheat Series 20 Commercial and Industrial Electric Water Heaters Brochure

Control of the Water Heater

Control wise – you basically control the power supply to the immersion heater or heaters fitted to the water heater.

This is done via a volt free relay or relays. These also are referred to as volt free contacts or dry contacts.

The volt free contacts are used to operate auxiliary equipment, sending closed or open contact signals to a Building Management Systems (BMS) or other logic level control system.

As the name suggests, there is no voltage present at the terminals. So, to operate the immersion heater, for example, you need to have a dedicated power supply which is then fed through the relay (typically the live feed) to switch it on or off accordingly.

ErP Directive for electric hot water heaters

All of our commercial and industrial electric water heaters are manufactured according eco-design Directive ErP, (Energy related Products), using a quality injected polyurethane foam insulation which is CFC free. The exterior finish of this insulation is a white polyester reinforced with fiberglass, which allows easy cleaning of the water heater and ensures its durability.

Required for all water heaters and storage tanks up to 500l, ErP energy labels have been required and since an update in September 2017 saw the energy ratings adjusted to run from A+ to F for commercial hot water heaters, and also limits for standing heat losses, which is the heat lost to the environment and that results in wasted energy for your hot water system. All of our commercial electrical water heaters are manufactured according to the EU directive 2014/68/UE and Standard EN13445, and directives ErP 2009/125 CE and energy labelling directive – ELD 2010/30/UE

Electrically heated water heaters are assessed against a “load profile” – which are a series of hot water profiles that reflect the usage of the water heaters of different capacities.
As electricity is viewed as a carbon intensive fuel, the efficiency of an electric unit is divided by a “fuel factor”, reducing its apparent efficiency. The next bit is infuriating, as many people, organisations and legislators, have tried to bring to the attention of the EU, that there are now many renewable energy sources used to generate electricity, such as wind, solar, wave etc. However, the EU has ignored this logical argument, and view electricity as a carbon intensive fuel, and as a result direct electric water heater now have a lower efficiency than an equivalent size indirectly heated unit.

Industrial electric hot water heater

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Industrial electric water heaters from Flexiheat UK, after 750 Litre in volume, our units come with an inspection plate / manhole option

All of our industrial and commercial electric water heaters are supplied Incoloy-sheathed heating elements, or sometimes these are called immersion heaters. These Incoloy heating immersion heaters generally are made from nichrome, which is mostly nickel-based, normally 80% nickel and 20% chromium. These qualities make them a good water heating element and are designed for excellent corrosion resistance, ensuring a long trouble-free product life.

Commercial and industrial electric hot water heaters for Sale UK & Ireland

Should you require anymore assistance or information on our Commercial electric water heaters /Industrial electric water Heaters or if you refer to them as commercial and industrial electric hot water heaters, then please don’t hesitate to contact our sales team on 01202 822221 or click here for our email contact form