70kW Boiler Gas Fired Condensing

70kW boiler gas fired condensing

70kw Boiler gas fired condensing boiler for central heating be it radiators or underfloor heating and domestic hot water in a environmentally friendly way from Flexiheat UK


Our gas fired 70kW boiler is available in natural gas or for LPG gas fuel (LPG biofuel compatible to). They are a high-performance “A “rated efficiency , “ErP” compliant condensing boiler and offer enhanced performance that exceeds the Part L building regulations for seasonal energy efficiency requirements. With low NOx Class 6 environmentally friendly emissions.

This regular boiler can be used for space heating, central heating (radiators or underfloor heating), and domestic hot water production via a plate heat exchanger or indirect domestic hot water calorifier or cylinder.

Efficiency features: with a modulation ratio of 20:1, the automatic part load adjustment offers superb outputs down to 3.5 kw of heat output, which leads to better heat load matching of the system, lower fuel consumption, and you’ll save on energy costs.

This energy efficient commercial boiler also has two stainless steel heat exchangers in one boiler, which ensures redundancy for your heating system; if one heat exchanger module fails, you still have up to 50% of your heat duty available. This feature can be vital for commercial customers on a site that can’t be without some heat.

The unit comes with a 2-year warranty for parts , and the heat exchanger has a 5-year warranty if, as required by the building regulations, a dirt and air separator is fitted to protect the system, and the product is serviced annually.

70 kW wall-hung gas condensing boilers

With the option of installing the boiler as a wall-to-wall solution or arranged on a suitable free-standing frame kit for floor-mounted installation, depending on site requirements.

Gas condensing boiler, which is a regular boiler on a free-standing frame kit the R1K range 50kw to 120kw outputs from Flexiheat UK

The 70kW gas fired condensing boiler mounted on a free-standing frame kit with low loss header and plate heat exchanger of domestic hot water production.

We can provide a solution for every commercial specification, as we can cascade these high performance gas boilers up to 960 kW with automatic part load adjustment if so required.

commercial gas boilers; commercial lpg boiler; wall hung gas commercial boilers; commercial boilers in cascade which are a regular boiler

70kW commercial wall hung boilers

As each boiler (heat exchanger) has its own flue non-return valve, you can service either boiler heat exchanger module without shutting the space heating system down.

Our energy-efficient gas 70kw boilers are fitted with fully modulating low NOx burners (Class 6 combustion levels) for lower environmental impact.

70 kW gas boiler with two heat exchangers for energy efficient low carbon central heating and domestic hot water via an indirect hot water cylinder the R1K75 from Flexiheat UK

Two heat exchangers for redundancy in one boiler casing with an output of 70 kW

R1K75 gas condensing boiler output and energy efficiency figures—Part L building regulations

The latest changes to Part L of the Building Regulations, which went into effect on June 15, 2023, say that all new wet central heating systems should be sized for a maximum heating flow temperature of 55°C (previously, 75°C plus boiler flow temperature was allowed), and preferably lower if possible to get the most condensing effect from boilers.

Thus, our gas boiler will produce up to 79.35 kW when the heating system flow and return temperatures are 50/30 °C.

The unit will also provide 72.83 kW at 80/60 °C if you have a process heating application that is not covered in the Part “L” building regulations.

Full data is shown in the following:

R1K75 gas condensing boiler output and energy efficiency figures Flexiheat UK

Output and energy efficiency figures for our R1K75


This is detailed in our full manual, which can be downloaded here.

Manual for R1K 75 Gas Condensing Boilers – Internal version Flexiheat UK

Should you require a larger output gas boiler (we do up to 240 kW in a single boiler and up to 980 kW in a cascade system, then we do a full range of gas condensing boilers, which are listed here.

Commercial gas condensing boiler range


  • “A” ErP efficiency rating wall-hung boiler designed for commercial use or a very large home domestic central heating systems and DHW for multiple bathrooms via a hot water cylinder.
  • Low Class 6 NOx flue gas emissions making these more environmentally friendly.
  • Straightforward and easy install: all plumbing connections are at the bottom of the unit saving installation costs.
  • Energy efficient condensing boilers up to 105.8 % at 100% heat input at 50/30°C
  • Stainless steel heat exchanger with 28mm diameter water ways that ensure the boiler benefits from very low pressure drops, guarantees lower risks of clogging (more resistance to fouling up), greater thermal efficiency, and greater ease of cleaning.
  • Intelligent fault system: if the boiler has a fault, it will tell you exactly what has gone wrong, i.e., if the heating system installation pressure is too low, etc.
  • Maximum heating operating system pressure = 3 bar
  • Maximum heating operating system pressure = 0.3 bar
  • An “Opentherm” thermostat controller, such as a “Hive” or “Nest” type, can control the boiler’s operation and temperature either locally or on the go using your phone, tablet, or computer. You can also use a basic thermostat; the choice is yours.
  • BMS compatible with our 0–10 volt free contact kit


Dimensions of this regular boiler: 70 kW Output for central heating and domestic hot water heating

This boiler has the following compact dimensions: 670 mm wide, 495 mm deep, and 642 mm high.

Dimensions of our 70kw condensing boiler gas fired in natural gas or LPG- ErP "A" rated for central heating (radiators or underfloor heating) and domestic hot water via a calorifier from Flexiheat UK

A small compact energy efficient gas condensing boiler 70 kW with ErP “A” rated for central heating (radiators or underfloor heating) and domestic hot water via a calorifier.

Connection details at the bottom of the unit: flow and return connections, gas connection, and condensate drain.

Connection details of the 70kW condensing gas fired boiler Flexiheat UK

Free standing frame installation detail

Floor standing mounting kit

Gas fired 70kw output condensing boiler on a free standing floor frame kit with low loss header Flexiheat

Boiler on our floor free standing frame kit with low loss heating system header option


70kW gas system boiler

Are these an 70kW gas system boiler? Yes, in that they have a pump (two pumps actually, i.e., one for each heat exchanger module), but at this size of system boiler, we can’t fit an expansion vessel within the boiler casing, so one needs to be fitted to the plumbing pipework external to the boiler to make the unit a full system boiler.

Flue options

Each heat exchanger module features its own flue exhaust connection. You can either individually flue each unit with a co-axial flue (80mm/125mm) should you wish to go room-sealed up to 10 metres vertically or horizontally in range. However, if you use a split flue system, you can go up to 40 metres vertically or horizontally in range.

The last option is a common flue header for the boiler.

R1K75 gas boiler with common flue header option

Common flue pipe header option

Gas fired 70 kW boilers

Should you require more product information, check stock, technical support, prices, or to order on our high performance 70kw boiler in natural gas or LPG, then please don’t hesitate to contact our sales team on 01202 822221 or use our email contact form via the contact tab above to message us. Follow our business on Facebook or Twitter if you’re interested in being informed of our latest recommend manufacturer product range items deal.