commercial combi boiler from Flexiheat UK;45 kw combi boiler;55 kw combi boiler;50 kw combi boiler;60 kw combi boiler;65 kw combi boilerFlexiheat UK

Commercial Combi Boilers

commercial combi boiler from Flexiheat UK;45 kw combi boiler;55 kw combi boiler;50 kw combi boiler;60 kw combi boiler;65 kw combi boiler

Commercial Combi Boiler from Flexiheat UK- Floor Standing Condensing Gas Fired  (natural or LPG gas )- 45kW , 55kW or 65kW Output


Commercial combi boilers or commercial combination boilers, whichever you want to call them, are generally considered to be the United Kingdom’s most popular type of boiler. A commercial combi boiler or combination commercial boiler is a very compact and highly efficient boiler, that not only supplies all the heating requirements, but also the hot water for the sanitary use, such as bathing or showering, washing up, food preparation, hand washing etc, from many applications such as larger households to commercial applications.

They ensure not only significant savings on installations costs, but also guarantee lower running cost too, making them the best choice from many larger domestic properties or commercial heating requirements, where heating and hot water are required.These boilers are floor standing condensing combi boilers, that can be fired with either natural gas or LPG ( propane ).These condensing boilers provide high efficiency energy generation with their “Premix Technology” and “Condensing Technology”.

Commercial Gas Combi Boiler Features and Benefits

Heating and domestic hot water thermal capacity of 45 kW , 55 kW or 65 kW outputs.

Environmentally-friendly with lower NOx and CO emission rates.

Prolonged high performance and high thermal efficiency as the boiler features a stainless-steel heat exchanger with enlarged pipe diameters

Various hot water storage tank capacity options according to the domestic hot water requirements you have, of either 60 litres, 90 litres or 120 litres

The comfort and usability of rapid hot water generation via our highly efficient indirect hot water tank

A high modulation ratio of 5:1, means these commercial combi boilers adapt to the heat output required, to suit the site conditions and elements.

Low operational noise levels and heat losses thanks to its configuration with high heat and sound insulation.

The ability to operate with Natural Gas or LPG (Propane Gas)

High efficiency circulation pump with automatic air purge, controlled via a PWM driver.

Simple control with easy-to-use illuminated LCD panel; you can viewing error codes and boiler information from this panel.

Superior safety features, such as ;
Flame safety control; ionization.
Flue gas temperature control.
Heating circuit overheating safety.
Frost protection.
Low water pressure safety system

Optional room thermostat connection.
Optional remote control.

Combination commercial boilers

A “true” combination boiler combines a water heater and central heating boiler in a compact unit, and usually uses a plate heat exchanger to produce the domestic hot water, which when a hot water tap is turned on, the boiler sends the heat produced from the heating side of the boiler , via a control valve to the plate heat exchanger , which then heats up the domestic hot water , until the hot water tap is turned off.

The heat these combi boilers produced can either be utilized by either the central heating system or to the domestic hot water taps, but never at the same time.This can cause some problems –

One of the problems with a commercial combi boiler is that they require good mains water pressure to achieve good hot water flow rates, and also a large enough plate heat exchangers to achieve this.

If you have a low mains water pressure, then it results in your hot water flowing out at merely a trickle, meaning showering becomes a poor experience, or that filling a bath literally takes for ever.

We at Flexiheat UK, have overcome these potential problems by producing a commercial combi boiler that has an element of domestic hot water storage, which can be supplied with cold water from either the mains supply, or a cold-water storage tank. Thus this boiler can really be classified as a “commercial combination boiler with hot water storage”, and we think its the best solution to these potential problems.

Combination Boilers Commercial – Advantages

1. Compact size – A commercial combination boiler is very compact having a small foot print when compared to the older traditional boiler and indirect cylinder set up found in commercial heating and hot water applications. Even though these boilers have a hot water storage element, due to the high recovery rates, they are much smaller in size, but give the same or even better performance!

2. Reduced installation time and cost – Also because they are mains water fed , there is no need for a cold water storage tank in the roof or loft space, which benefits with installation costs, as less pipework and labour time is required to fit one of these boilers whilst removing the potential of these pipes or water tank freezing in the British winter period – another benefit.

3. Excellent efficiency– These commercial combi boilers are up 109% efficient, when working on a 30% heating load at 30 Degrees C ( typically an underfloor heating system) , and are 98% efficient at the minimum load when being used on an 80/60 Degrees C heating system ( typically an older radiator designed system ) .Heating a larger home or commercial building is therefore more affordable when compared to conventional non condensing boilers.

Combi Boiler Technical Data

TECHNICAL SPECIFICATIONSFH-S DHW      45SFH-S DHW      45MFH-S DHW      45LFH-S DHW      55SFH-S DHW      55MFH-S DHW      55LFH-S DHW      65SFH-S DHW      65MFH-S DHW      65L
Thermal Capacity
Maximum Heating CapacitykW454545555555656565
Minimum Heating CapacitykW11111112121213.513.513.5
Maximum Heat Discharge for Heating (80°C / 60°C)kW42.442.442.453.453.453.4646464
Minimum Heat Output for Heating (80°C / 60°C)kW7.
Maximum Heat Discharge for Heating (50°C / 30°C)kW45.845.845.857.
Minimum Heat Load (50°C / 30°C)kW8.
Maximum Domestic Water CapacitykW44.244.444.854.154.554.764.264.664.8
Thermal Efficiency
Efficiency @ Pmax. (80°C / 60°C)%97.497.397.797.597.397.797.397.297.2
Efficiency @ Pmin. (80°C / 60°C)%98.598.698.798.899.198.20%98.698.398.6
Efficiency @ Pmax. (50°C / 30°C)%105.2105.3105.4105.3105.2105.1105.6105.3105.6
Efficiency @ Pmin. (50°C / 30°C)%107.4107.6107.2107.2107.2107.2107.1107.3107.4
Efficiency @ 30% (30°C)%108.7109108.2108.1108.7108.5108.6108.4108.7
Domestic Water Circuit
Domestic Water Temperature Adjustment Range°C10 -6510 -6510 -6510 -6510 -6510 -6510 -6510 -6510 -65
Domestic Water Storage Tank VolumeL609012060901206090120
Domestic Water Flow Rate in ContinuousL / dT12.118.424.
Use (∆T=25°C. 20 °C /45 °C)
Heating & DHW Pressures
Maximum Operating Temperature- Heating°C858585858585858585
Maximum Operating Pressure- HeatingBar444444444
Minimum Operating Pressure- HeatingBar0.
Maximum DHW PressureBar666666666
Gas Properties
Gas TypeG20-G31G20-G31G20-G31G20-G31G20-G31G20-G31G20-G31G20-G31G20-G31
Gas Inlet Pressure (G20) Natural Gasmbar202020202020202020
Gas Inlet Pressure (G31) LPG /Propane Gasmbar373737373737373737
Combustion Values
Maximum Flue Gas Outlet Temperature (50°C / 30°C)°C424242444444454545
Maximum Flue Gas Outlet Temperature (80°C / 60°C)°C656565656565656565
NOx Emission  Class (EN 15502-1+A1)555555555
Electrical Values
Voltage & FrequencyV / Hz230/50230/50230/50230/50230/50230/50230/50230/50230/50
Energy ConsumptionW190190190210210210300300300
Hydraulic Circuit Properties
Gas Connectioninch1/2”1/2”1/2”1/2”1/2”1/2”1/2”1/2”1/2”
Heating Circuit Flow & Return Connections inch3/4″3/4″3/4″3/4″3/4″3/4″3/4″3/4″3/4″
Domestic Water Circuit Flow & Return Connections inch1/2″1/2″1/2″1/2″1/2″1/2″1/2″1/2″1/2″
General Features
Net (Dry) Weightkg95110125100115130105120135
Flue Diameter (Ø)mm80/12580/12580/12580/12580/12580/12580/12580/12580/125
** G20 Natural Gas.    G31 LPG

As you can see from the chart above our commercial combination boilers are available in either natural gas or LPG propane gas fuelled.

Combi Boiler Hot Water Performance

Having a hot water storage capacity in our commercial combi boilers has advantages over a combi boiler that uses a plate heat exchanger.

As a commercial combination boiler draws all of its water supply directly form the mains water supply, they can often struggle to meet high water demands, we have all seen what happens when a person turns on a hot water tap when someone is having the shower, and the dramatic drop in water pressure , normal followed by a shout “ turn that tap off “ I’m having a shower , this is due to the fact that a true combination boiler has no storage tank like our units, which over come this problem, and allow multiple hot water taps or outlets to be used simultaneously.

Filling a Bath

Since a traditional commercial combination boiler draws its water directly from the mains and not a water tank, you will find a combination boiler requires more time than a traditional boiler fitted with a separate indirect hot water tank to fill a bath. Again, this is something over come when using some hot water storage capacity.

According to BS6700 a standard bath tub (1700mm x 700mm) full capacity is around 180 litres to overflow level, but most people full their bath tubs to around half way to allow for the displacement of water when they get into the bath. So, the actual volume of water used is 100 litres.

The normal bath water temperature is around 40 Degrees C

When you have stored water, this is kept at 60 Degrees C to prevent legionella, which is then blended down with cold water to achieve the 40 Degrees C, at a ratio of 60% hot water and 40% cold water, or 60 litres of hot water and 40 litres of cold water

Thus, a bath cycle requires 60 litres of hot water, stored at 60 Degrees C.

Our commercial combi boilers come with the option of three different sizes of hot water tanks inbuilt into the casing of boiler, for all the models.

The options are a 60-litre hot water tank, a 90-litre hot water tank or a 120-litre hot water tank

Thus, you can have a 45 kW combi boiler, with either a 60, 90 or 120 litre hot water tank

A 55 kW combi boiler, with either a 60, 90 or 120 litre hot water tank

Or the largest unit

A 65 kW combi boiler, again with a 60, 90 or 120 litre hot water tank

Our commercial combi boilers come with the option of three different sizes of hot water tanks inbuilt into the casing of boiler, for all the models.The options are a 60-litre hot water tank, a 90-litre hot water tank or a 120-litre hot water tank

Thus, you can have a 45 kW combi boiler, with either a 60, 90 or 120 litre hot water tank ,or a 55 kW combi boiler, with either a 60, 90 or 120 litre hot water tank or the largest unit a 65 kW combi boiler, again with a 60, 90 or 120 litre hot water tank

Where our commercial combination boilers excel is in the hot water recovery rate. this can be defined as the amount of time that it takes to recover the heat in the hot water storage tank, when it has been completely drained. In reality this rarely happens, as the boiler starts to replace the hot water as it’s being used.

But hypothetically, lets look at the recovery rates, at the time of the year, when you need your domestic hot water performance to be at its best – winter time. On average the coldest mains incoming water temperature is 5 degrees C, and we would want to heat this water up to 60 degrees C.

If you look at the above data chart, you can see how many kW these commercial combi boilers can use for the heating of the domestic hot water.

For example, the 45 kW combi boiler, has a maximum domestic hot water capacity of 44.2 kW for the 60 litre hot water tank, 44.4 kW for the 90 litre hot water tank or 44.8 kW for the 120 litre hot water tank. But let’s call it 44 kW for the purpose of the calculations.

The 60 litre tank, would recover it’s hot water in 5.30 minutes, the 90 litre in 4.30 minutes and the 120 litre unit in 5.70 minutes, which is very impressive hot water performance indeed.

The figures are even better for the 55 kW combi boiler and the 65 kW combi boiler that we supply.

commercial gas combi boiler;light commercial combi boiler;commercial combination boiler;50 kW combi boiler;55 kw combi boiler;60 kW combi boiler;65 kW combi boiler

Internal diagram of our commercial combi boiler

Flue options for these combination boilers

The full range of these commercial combination boilers can be flued in various ways. The most common is a co-axial flue system, which makes these commercial combi boilers a room sealed appliance, meaning that the combustion air (the air feeding the burner on the boiler) is brought in from the outside environment to the boiler.

These combi boilers can be flued in a co-axial system  –

Horizontally- up to 10 metres in total length, with the use of each 90 ° elbow reducing this length by 1 metre, and the use of each 45 ° elbow reducing it by 0.5 metres


Vertically – up to 11 metres in total length, with the use of each 90 ° elbow reducing this length by 1 metre, and the use of each 45 ° elbow reducing it by 0.5 metres

Combination Boiler Controls

These commercial combination boilers have an easy to operate control panel, which is an “OpenTherm Plus” protocol control panel, which basically means you can control these commercial combi boilers, via the use of an OpenTherm controller, such as a “nest” type or similar. This means you can make your life simpler and control these commercial combination boilers from either your mobile phone (android or apple) your PC or tablet, from anywhere in the world.The control panel also has numerous inbuilt features such as –

  • Full protection against freezing of the heating and domestic hot water in low ambient temperatures
  • Ability to operate according to different heat demands with the variable flow pump control
  • Anti-blockage System -The circulation pump is activated automatically once every 24 hours and prevent any blockage
  • Low fuel consumption and fixed combustion efficiency thanks to the PWM driver, high modulating fan and high modulating gas valve
  • Ability to operate according to different heating system configurations
  • Ability to control these commercial combi boilers  by Android and IOS operating system
commercial combination boiler; commercial gas combi boiler; light commercial combination boiler; 60 kw combi boiler; 50 kw combi boiler; combi boiler commercial

Commercial Combination Boiler – Control Panel

Gas Fired Combi Boiler – Heavy Domestic or Commercial

We often get asked when does the classification of a commercial combi boiler start, well there is no hard and fast rule. We look at this way –
A standard new build house in the UK will use a combination boiler that at most is 30 kW these days
But a domestic gas engineer registered with Gas Safe can work on appliances up to 70 kW net if the gas system has a gas volume less than 0.035m³ with a flow rate up to 6 Metres cubed per hour and the pipework is less than or equal to 35mm in diameter, which covers all of this range.

Therefore, it is almost better to classify these boilers suitability / applications by description –

Heavy domestic houses / properties – these would typically be the following –

45 kW combi boiler – a larger property that requires a heating load of 45 kW, with –
1 or 2 Bathrooms – then typically the 60 litre hot water tank combination boiler will suffice
2 or 3 Bathroom – then typically the 90 litre hot water boiler tank combination boiler will suffice
3 or more bathrooms – or a large hot water usage property / lifestyle then your looking at the 120 Litre tank combination boiler
It would be the same for the 55kW combi boiler or the 65 kW combi boiler version, just that the heating requirement for the property would be larger. So, these would typically be larger detached properties, mansions or large country houses.

On the Commercial property applications, you would be look at –

Doctor and dental surgery’s
Schools and colleges
Retail / shop outlets
Commercial and smaller industrial units
Bed and breakfasts establishments / Even smaller hotels

They can be used in a commercial heating application with a radiator or underfloor heating system, or with warm air hot water unit heaters, which we supply.

commercial boiler

So if you require the best commercial combi boiler for sale on the UK market, that can be used in either commercial applications or large properties , then please don’t hesitate to contact us at Flexiheat UK, using the contact us function at the top of this web page, or alternatively give us a call on 01202 822221