Gas fired water heaters from Flexiheat UK; tap; gas water heaters;Flexiheat UK

Gas Fired Water Heaters

Gas fired water heaters from Flexiheat UK; tap; gas water heaters; gas fired hot water cylinder

With a full range of gas fired water heaters from 28kW to 50kW of  domestic hot water output, for applications from domestic properties to commercial water heaters for high volumes that are often required for schools, hospitals or manufacturing or process applications etc,Flexiheat UK has a solution for you.

50kW gas fired calorifier

Our largest gas fired water heaters are designated the 50/330 and are industrial / commercial water heaters – This 50kW condensing gas-fired direct water heater that raises water from 10°C to 60°C on demand, providing domestic hot water at a rate of 871 litres per hour while maintaining outstanding efficiency and low NOx emissions that comply with ErP regulations for heating water – This water heater has a “A” rating . This gas water heater features a 330-liter storage tank with a fully enamelled heat exchanger enclosed therein for heating water, and it has a 50kW power output from a pre-mix gas burner (natural gas or LPG options).

A picture of a gas hot water tank or gas fired hot water cylinder from Flexiheat UK, which are used for water heating in large domestic, commercial, and industrial applications. These units are condensing gas water heaters.

Gas water heaters with storage systems for high volumes at intermittent times demand. These condensing water heaters are energy efficient and cost effective to run.


Technical data for the 50kW gas water heaters



50kw gas condensing storage gas water heater performance detail Flexiheat UK


Water heating recovery and flow rates for the 50kW Gas fired water heater with storage

50kW gas fired hot water storage cylinder water heating performance data-Flexiheat UK

Flow data at a storage temperature of 60C – incoming water temperature of 10C – mixed water temperature of 38C

You can download the brochure on this water heater here

50kW Gas condensing storage water heater brochure – HY model – Flexiheat UK

Next we have our 34kW and 28kW gas water heaters, designated the “SFKA” range, which are available in natural gas or LPG (propane)

This series of gas fired storage water heaters, are condensing water heaters that have a storage capacity of 150 Litres and are extremely thermal efficient – higher than 105% with low Nox emissions. The water heaters storage volume has been designed to provide enough instant hot water to the hot water heating services such as taps, showers, or filling baths at a constant temperature and flow rate, that you can’t achieve with multi point water heaters, which can suffer from low flow rates.

These water heaters deliver a reliable solution for larger domestic properties or commercial applications such as restaurants, shops, health centres ,fast food outlets, and pubs that demand good flow rates of warm water or high volumes of hot water at intermittent times for their use or their customers.

We do two models within the “SFKA” water heater range as it’s designated – These products are ErP “A” rated for efficiency condensing water heater and are sometimes called a gas fired hot water cylinder or gas storage water heater, as this gas fired water heater range has hot water storage to accommodate peak demands.

28kW gas fired water heater which is condensing– with a 150 Litre stainless steel storage tank – Which will provide a continuous D.H.W. supply – ΔT 30°C hot water temperature – of mixed water , in  1 hour of 984 Litres of flow rate – and a first 10 minute flow of 305 Litres


34kW gas fired water heater which is condensing  – with a 150 Litre stainless steel storage tank – Which will provide a continuous D.H.W. supply – ΔT 30°C hot water temperature – of mixed water , in  1 hour of 1,167 Litres of flow rate – and a first 10 minute flow of 333 Litres

Both heater models are available in natural or propane (LPG) gas powered options.

However, should have domestic hot water flow rate on the lower side, then you can look at our on-demand water heaters – please look at our webpage – gas multipoint water heaters – these are condensing gas instantaneous water heaters / tankless water heaters or flow water heaters with stainless heat exchangers which provide instant hot water performance without the need for hot water storage cylinders as they may be a better water heater solution, even in commercial water heating applications.

These gas water heaters are available in natural gas (mains gas) or LPG fired and are commonly used for feeding shower systems directly without the need for boilers and indirect calorifiers systems.

Condensing Water Heaters – ErP “A” rated

Condensing gas fuelled water heaters combine many benefits such as high levels of energy efficiency with low NOx emissions and cost-effective operating costs.

A highly efficient condensing gas fired continuous flow water heater is combined with a well-insulated stainless steel water storage tank to make one complete gas storage water heater / water heating system – that provide excellent flow rates- something instantaneous electric water heaters can not achieve. This gas water heater range are far more energy efficient than an older technology non condensing gas fired water heater or storage systems.



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Gas fired condensing storage water heater or gas hot water tanks from Flexiheat UK

This ensures occasional times of peak hot water usage can be satisfied by combining a condensing large capacity water heater with a domestic hot water storage cylinder, in an efficient gas fired water heater range. These condensing water heaters are highly energy efficient and are a perfect replacement for an instantaneous electric water heater which at this output require a lot of Amps to feed the units, and are therefore not practical.

Gas fired water heater product information

Compact, stand-alone water heating appliances or units for producing safe and clean domestic hot water –

Gas fired (hot) water production – sanitary quality hot water –  suitable for larger houses to commercial and industrial applications.

Water heaters that run on natural gas (mains gas)or LPG ( propane )are available.

Reduces energy consumption and operating expenses by optimising condensing water heating performance. With an thermal efficiency higher than 105%

The stainless steel heat exchanger with a 28mm diameter and a modulating gas burner minimize the possibility of scale build-up.

It benefits from very low pressure drops, guarantees lower risks of clogging, greater thermal efficiency, and greater ease of cleaning of this condensing water gas fired range.

Closely matches water demand and hot water temperature water, with 1:9 modulation for greater efficiency and reduced energy consumption for your desired temperature.

These are direct fired gas water heaters, so there’s no heat exchanger coil located in the storage cylinder

The inbuilt pump ensures even heat distribution and reduces the chance of hot water temperature stratification in this direct fired water heater range.

No clearances are required at the back, and minimum clearances at the top and sides allow for installation in any location or a plant room.

Making these commercial gas water heaters a great solution for heating water when space is limited.

Suitable for LPG gas combustion –

Can be fired by propane gas – With a maximum gas inlet pressure of 45 mbar for these commercial products

Suitable for mains gas (natural gas) combustion –

Can be fired by natural gas – With a maximum gas inlet pressure of 25 mbar for these commercial products

Enhance functionality and reliable control function –

You can use the inbuilt control panel or use an “OpenTherm” compatible controller for local or even remote management via a PC, tablet or phone of our gas fired water heaters. They can also be connected to a separate BMS system, using a 0-10V communication card.

Anti-legionella systems –

A vital safety function ensures that the gas water heaters storage tank is taken above the temperature required to kill any legionella in the gas water heater.

Flexible and multiple flue options –

This range of gas powered water heaters can be room sealed with a co-axial flue system, or up to a remarkable 60 metres when using a twin flue system, which is a great provision when being used in a commercial site or industrial applications

Storage tank anti-freeze system –

To ensure safety and that the water heater functions properly, the water heaters have an inbuilt sensor that automatic detects a water temperature below 5°C, the pump activates and the gas water heater raises the water temperature up to 30°C.When this temperature is achieved, the burner turns off and the pump runs for a further 20 seconds as post circulation for these low NOx gas water heaters.

28kW Gas hot water tanks specification – for domestic or commercial installation

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Then our larger 34kW gas water heater model

34kW Gas hot water tanks specification – domestic or commercial installation

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The full technical manual which covers both has water heaters, can be downloaded here  –

Download the SFKA 28 /150 and SFKA 34/150 Gas fired condensing storage water heaters manual all versions – Flexiheat UK 

Hot water system

The gas fired water heaters can be used in either a direct or a recirculation DHW system. See schematic view below –

Domestic hot water system options;gas hot water tanks

Gas hot water tanks – Direct feed or DHW Recirculation options

Solar water heater

We also manufacture a gas boosted solar water heater or solar gas water heater option whereby you can supplement this gas fired hot water heaters with solar energy. Solar water heating is of course carbon neutral.

Our solar gas water heaters or gas boosted solar water heaters comes in two options –

Solar gas water heater option with or without domestic hot water recirculation from Flexiheat UK

Solar gas water heater – the middle schematic shows the standard option, and the right-hand schematic shows the gas boosted solar water heater with DHW recirculation.


SFKA 150 SOLAR with 150 Litre stainless steel cylinder with a heating coil dedicated to a solar panel, with probes, circulator and solar control unit already connected. The solar water heater makes the most of the free heat of the sun using the gas water heater only heating water when required to top the solar heating up. The electronic control valve guarantees a perfectly constant supply of hot water, without temperature fluctuations.

or with the option of  DHW recirculation system

SFKA 150 SOLAR PLUS with 150 Litre stainless steel cylinder with coil dedicated to a solar panel, with probes, circulator, and solar control unit, and a DHW recirculation.

Gas water heating

Should you require a price, more information or we can assist or support you further on the best gas fired water heaters or water heating systems, please don’t hesitate to contact our team a call on 01202 822221 or contact us via our contact form above on the website.