24KW Combi Boiler – Combination boiler

24kW Combi Boiler

24kw gas fired combination boiler - condensing - model R2C24 from Flexiheat UK

A 24 kW combi boiler is an ideal new boiler that is suitable for a smaller one or two bedroom homes, apartments or flats.

Because there isn’t much space to heat in these-sized properties, there are normally fewer than ten radiators (the average size of radiators in a new build property is 1.5 kW). There is also less demand for domestic hot water in the property because they frequently have a shower or a single bath that can’t be used simultaneously.

Our 24 kW combi boiler is a small boiler that provides both heating and hot water on demand which eliminates the need for cylinders or storage tanks.

With a central heating output of 24.79 kW at a 50/30C flow and return temperature and a domestic hot water output of 11.5 Litres a minute with a 30C hot water temperature rise for this boiler type.

With its compact dimensions, it is designed to fit into a standard 350mm deep kitchen cupboard unit and has a low lift weight, which makes them the right combi boiler for these types of properties.

These combi boilers are are available in natural gas or LPG ( propane) gas and benefits from great features such as a large digital display for easy of use as well as a reduced noise level.

This gas combi boiler has an ErP rating of : Water heating efficiency “A” and a space heating efficiency “A”  – for this combi boiler size, thus reducing energy usage.

Having this 24kw combi boiler installed we can cover the hot water demands for most small to medium homes or flats with a single bathroom, without the need for a hot water cylinder, with the units being powered by either natural gas or propane (LPG).

A new boiler or a replacement should always be installed by a Gas Safe registered engineer.

Instant warm water on demand

The instant hot water system, provides energy efficient hot water to the taps or bathroom with no hot water storage tanks in small to medium homes, and that’s why the Energy Saving Trust recommends a high efficiency combi boiler as well as multiple heating engineers, when installing a new heating system or to replace an existing non condensing combi boiler in your flat or smaller property.

Larger properties, with more bathrooms will have a higher demand for instant water , and require a larger boiler size to achieve the local availability of warm water to the hot tap or showers through the home – as a boiler guide we do a 35kW combi boiler ( typically to suit a three bedrooms home for example) and a 50kw combi boiler suited or capable of doing more rooms such as a 4 or 5 bedroom property depending on related factors such as available mains water flow rate to the home. The 50kW combi boiler version has its own dedicated webpage, that shows all its features and performance data here : 50kW combi boiler

High efficiency combi boiler

All boiler manufacturers have since 2005 , have had to make a high efficiency combi boiler which is condensing in operation to help reduce carbon emissions via the combi boilers lower carbon-footprint. It has been mandatory to install condensing boilers, whether they are combi boilers or system type boilers.

Our easy-to-use combi boiler is “A” rated for both heating and hot water, making it a high-efficiency combi boiler for medium homes or smaller homes.

Hot water heat exchanger

The 12mm diameter internal stainless-steel pipe where domestic hot water is produced, is inside the patented stainless steel heat exchanger (28mm diameter) which ensures excellent reliability. Its total length is 8 meters, and this ensures you have a volume (approximately 6 Litres) of “warm water ready to go” as they say. The DHW production is always available and always in condensing operation, resulting in lower energy costs and bills for these combi boilers.

combi boiler heat exchanger manufactured in stainless steel with large water ways to prevent blocking

Stainless Steel heat exchanger with large water ways to prevent blocking in our combi boiler range

This design feature also reduces the chance of scale, something that older technology combi boilers that use a plate heat exchanger can suffer from. This is incredibly important in hard water areas– as our heat exchanger, with its high velocity and flexing in operation, reduces the ability for scale to build up, and prevents this happening ensuring a long life 24kw combi with trouble free operation and a good hot water flow rate.

Scale blocking the heat exchanger - older technology heat exchanger systems for DHW production

Scale blocking the heat exchanger – older technology heat exchanger systems for DHW production

This unique and clever engineered solution for our heat exchanger system provides many advantages as opposed to most boiler manufacturers that use a traditional separate plate heat exchanger system, for the domestic water. This why many consider our 24 kW combi boiler the best combination boiler on the market in the UK, with high reliability at a fair market price or cost.

Central heating system or space heating of the combination boiler

A combi boiler provides warm water for radiators or an underfloor heating system or any other type of space heating, with our compact 24kw combi model having a hot water (DHW) priory system. The total heat requirement (radiators ,underfloor heating etc) should not exceed 24.79 kW of heat output based on a 50/30C flow and return heating when in operation on the coldest of days for this boiler size.

How many radiators will this boiler size cope with – generally in a new build – 10 average size radiators

Specifications of the R2C24 combi boiler 24 kW condensing boiler

The models comparison of technical data, is covered in the picture below.

Please note that the central heating output of this 24kw combi depends on the flow and return temperatures to the heating system, i.e., at 50/30C it will produce 24.79 kW, or if it’s 80/60C then the output is 22.7 kW. The domestic hot water output doesn’t vary; this is a constant.

R2C24 combination boiler - natural gas or LPG gas - technical data Flexiheat UK

Hot water flow rate -11.5 Litres/minute in typical winter time – when you need warm water the most !


and in more detail in the manufacturer manual – which can be downloaded here –

Download the Flexiheat R2C 24kW Combi  Manual


Our 24 kilowatts combi boiler dimension details are generally – Height = 642 mm , Width = 410 mm  and a Depth of 307 mm –  making the units easy to fit in any installation with in line hydraulic connections at the bottom of the 24kw combi boiler.


R2C24 24kw combi dimensions - natural gas or Lpg fuel options

24kW Combination boilers with high modulation

Our combi boilers have an exceptionally high modulation range or ratio of 1:9 for this size boiler, which means our 24kw combination boiler will ramp all the way down to 2.9 kW of heat output. This high modulation range ensures the closest of heat load matching to the properties demand, which results in lower heating energy bills.

Frost protection

These combi boilers fire up when the water temperature drops below 5 °C within the heat exchanger, automatically starting the burner until the heating water reaches the temperature range of 30 °C. This frost protection system will protect the boiler up to an external temperature of -10 °C.

Flue lengths and options

With extensive flue lenghts options of up to 60 metres in flue length – when using a sperate 80mm diameter twin flue system, or up to 10 metres in length when using our 60/100mm or 12 metres maximum horizontal flue for our 80/125mm co-axial horizontal flue system option (which most people go for)- Both systems make these combi boilers a room sealed gas appliance.

Horizontal flue kit co-axial room sealed for our boilers Flexiheat UK

Horizontal flue kit co-axial – 60/100mm Ø will go 10 metres , or the 80/125mm Ø option will go 12 metres in flue length

Or our vertical flue options

Vertical flue kit co-axial for our boilers Flexiheat UK

Vertical flue kit co-axial – 60/100mm Ø will go 10 metres , or the 80/125mm Ø option if your require more height – will go 12 metres in flue length

Control options

All our boiler sizes, be they the 24kW, 28kW or 35kW outputs or models can be controlled via the inbuilt digital display or you can opt for our smart thermostat range option, which is an open-therm control system, which allows you to control these combi boilers from an app on your phone, tablet, or computer in a user friendly manner.Simply click on the app to control your 24kw combi boiler, its as easy as that !.

cloud warm app to control the boiler from your mobile phone or tablet

Cloud Warm App – control on the go !

Nest and Hive controllers are Opentherm compatible, so you can use these with what we consider the best boiler on the market.

An Open-Therm thermostat controller is a smart controller which helps your central heating run in an more energy-efficient state, as they can optimize and weather compensate the heating systems to the external weather conditions – Explained very well in the following video –


Condensing boiler installation

As gas safe heating engineer installer, normally with local availability must be used to ensure a safe installation ( always check their company registration number with the gas safe register) and to provide a labour warranty on the 24kw combination boiler install.

Contact us

Our 24kw combination boilers are the ideal boilers for a smaller house, apartment or flat, with its compact dimensions this size boiler can fit in a kitchen cupboard if so required. Should you require anymore assistance, information or price on the best 24kw combi boiler  in natural gas or LPG on the UK market, please contact our sales team on 01202 822221 or use our email contact above on the web page for our email contact form to get free boiler quotes. All of sales are supplied with a vat invoice.