External Gas Boilers

External Gas Boiler – We have a full range of external gas boilers rated from 3kW to 2,240 kW that can be fuelled by either natural gas or LPG Gas. The smaller boilers are wall hung, and the large boilers are floor standing. The range consist of three external gas boiler ranges which cover the range from 3kW to 2,2240kw, and all of the external gas boilers feature either one of the patented stainless steel heat exchangers , these being a R.V.C Heat Exchanger – which stands for Radial Variable Circulation or a R.S.C. Heat  Exchanger – which stands for Radial Shared Circulation . The benefits of these heat exchangers are listed below –

External Gas Boiler – Heat Exchanger Features

EXCLUSIVE PATENTED DESIGN – Since the early 90’s the development of condensing technology designing has resulted in two exclusive primary heat exchangers , the R.S.C. and R.V.C. Heat exchangers

EXCEPTIONAL RESISTANCE AGAINST CORROSION – The 3 series of stainless steel round tubes, which the heat exchangers are made of, are fasten without weld joints to grant the highest resistance against corrosion.

HIGH EFFICIENCY – Both heat exchangers have been designed to reach an optimal exchange along the entire lenght of the exchanger and to grant an exceptional efficiency of up to 110% with savings on your heating bill of up to 35%.

R.V.C. HEAT EXCHANGER -Radial Variable Circulation, with stainless steel AISI 316Ti (Titanium) non wet chamber without weld joints to keep unaltered the characteristics of stainless steel, housed inside a resistant self-supporting monobloc made of insulating composite.


External gas boiler heat exchanger

RVC Heat Exchanger – Stainless Steel 316 T1 Titanium – Up to 11 Bar Rated


R.S.C. HEAT EXCHANGER -Radial Shared Circulation, with AISI 316L stainless steel wet chamber, to grant the highest resistance to corrosion,housed inside a resistant self -supporting monobloc made of stainless steel.


External gas boiler 316 heat exchanger

Radial Shared Circulation – Stainless Steel 316L



The external gas boiler heat exchangers are made of 3 series of round tubes (18 and 16 mm diameter), to avoid clogging and to grant:
– HIGH WORKING PRESSURE (up to 11 bar)

Gas boiler heat exchanger , stainless stell heat exchanger, boiler heat exchanger

Large Water Ways – Means Large water flow, greater heat exchange surface , lower pressure drops , and higher working pressures – up to 11 bar


During the external gas boiler operation, return water is distributed through Ø16 and Ø18 mm round tubes series.The advantage of such a system is to condense with 55/56°C temperatures of the return water and to have excellent outputs of the boiler even in radiators systems. In the R.S.C. heat exchanger fluid circulation is radial shared, while in the R.V.C. heat exchanger it is radial variable – see the schematic below

External Gas Boiler Schematic

Boiler Combustion and Heat Transfer Schematic



The “variable” circulation of the fluid allows a flue gas/water upstream thermal exchange, this sets up a high efficiency that quickly leads to flue gas condensing.



The innovating premix and cascade sequence control system employed in these external gas boiler range allows an exceptional turndown ratio from 1:6 to 1:20 (and even more in case of boilers in cascade sequence).
Turndown ratio from 1:6 to 1:20
Negative pressure gas valve
It also operates with low gas inlet pressure up to 7,5 mbar
Constant air/gas ratio

Gas Premix Burner, Gas Premix Boiler

Gas Premix Burner – a constant air/gas ratio in each point of the turndown range of the burner, decreasing polluting emissions and streamlining efficiency



Ecologic premix boilers have a constant air/gas ratio in each point of the turndown range of the burner, decreasing polluting emissions and stream lining efficiency. The gas premix burner is made of “Fecralloy” a special metal fibre and has a round shape. The premix burner spreads short and perfectly nourished flames.
High-efficiency combustion
Low polluting emissions (CO<15 ppm and NOx<15 ppm)
Natural gas and LP gas operation


MYdens is the new concept boiler born to satisfy current housing / residential field needs, characterized by increasingly tight spaces,energy saving, comfort, and reliability. The output options on this range are 15kW , 24kW or 34kW

COMPACT AND ELEGANT – Only 305 mm depth contains all the power of MYdens in an elegant and refined design.Its small size and light weight simplify installation. It has been given great attention to the user usability with simple and intuitive controls, and ease of maintenance with front access to the boiler.A  range of condensing gas boilers able to satisfy the new household needs,
that feature smaller spaces, energy saving requirements, comfort, ease of use, reliability and a light impact on the environment.

External combi boiler gas fired

Mydens Condensing Gas Boiler – 15kW – 24kw -34kW Output Range















If you order the MYdens in the external combi boiler version, this external gas boiler benifits from an over sized plate heat exchanger, the domestic hot water is produced by an oversized stainless steel plate heat exchanger (Length=320 mm), that allows great and quick availability of D.H.W. Moreover Q30 always works in condensing mode, even during domestic hot water supply, thereby reducing the consumption and costs involved in the production of hot water of an additional 10% – compared to boilers that do not condense during D.H.W. production.

This external gas combi boiler range always works in a condensing mode, both in heating and hot water production, thereby reducing the consumption and costs involved in the production of hot water of an additional 10%.Considering that hot water is used 365 days a year, the choice of  these External Gas Boiler’s double condensing means a great increase in savings!

The Mydens range of gas condensing boilers is available for use outdoors with the additional COVER-BOX, the CE certified, insulated,  and weather resistant cover made of anti-UV ABS. The polyethylene insulation, high insulation capacity,fireproof, gives an IPX5D electric protection degree and protects the boiler from frost.The CR04 Boiler Remote control allows remote control over the external gas boiler internally from the house or building.

Flexiheat Brochure for External Gas Boilers


The MYdens 60 model is a commercial wall hang heat only gas condensing 60 kW boiler. It is ideal for small business and multi-family users, and can be connected in cascade sequence up to 8 units to achieve a maximum power of 462 kW.This boiler is an A rated ERP product

COMPACT, LIGHTWEIGHT AND ECOLOGIC – Only 44kg for 57,8 kW output. MYdens 60 is extremely ecologic thanks to the premix burner made of “Fecralloy” fiber which develops short and perfectly nourished flames.

WIDE TURNDOWN RATIO 1:8 – thanks to patented air/gas premix system ,the boiler output adapts according to real need for room heating, guaranteeing great gas savings and low CO2 emissions.

60 A without pump, without expansion vessel
60 C with built-in pump, without expansion vessel

Usually a standard condensing boiler works in condensing mode only in combination with low temperature heating systems. This happens because the floor heating installation works with water
at low temperature and the condensing boiler reaches its maximal efficiency at this condition. But traditional radiators need to be heated with high temperature water and traditional condensing boilers do not condense when they work at high operating temperatures. Thanks to the innovative, wide surface,patented R.V.C. heat exchanger of MYdens 60 flue gases condense at 55°C return temperatures,working always in condensing mode also in installation with radiators.For this reason MYdens 60 is the ideal condensing boiler not only for new installations,but also in the replacement market.

Flexiheat Brochure for External Gas Boilers

Larger External Gas Boiler Range , Floor  Standing , IP5XD Rated , For External Locations 


These Larger external commercial gas boilers are produced from 65 kW to 300 kW is and are modulating commercial gas condensing boilers, completely fully assembled  , in a floor standing external gas boiler configuration.These external gas boilers can be cascaded up to 2,240 kW of Heat Output , if so required.

External Gas Boiler Larger Sizes, External floor standing condensing gas boiler,large external gas boiler

  • 10 different capacity option between 65 kW-300 kW in ECODENSE RT One or Twin series (i.e one boiler or two boilers)
  • High efficiency with premix condensing technology and ecologic micro-flame metal fiber coated steel burner
  • Provides energy saving through 5:1 modulating operation,that optimizes the supplied output according to real thermal needs of the heating system – ensuring maximum efficiency, and allow high seasonal efficiency in systems characterized by frequent and high output variations.
  • Can be fueled by natural gas or LPG
  • Easy hydraulic and gas circuit connections,
  • Allows simple control with illuminated LCD panel which provides ease of use; and error codes and boiler information can be displayed on this panel,also cascade sequence control of the boilers
  • Daily and weekly operation schedule can be programmed,
  • Seasonal heat program can be prepared during summer and winter times,
  • Operation in lower noise values,
  • Environmentally-friendly with lower NOx and CO emission rates,
  • Easy installation, operation and maintenance.Thanks to their relative lightness they are easy to maneuver  and to place to the location desired
  • Aluminum spiral heat exchanger – Each heat exchanger is made without weld joints and it is able to bear a working pressure up to 6 bar.If you require a higher working pressure, then you can use a plate heat exchanger to separate the boiler circuit from the heating circuit

External Gas Boilers,large external gas condensing boilers

Why choose an External Gas Boiler:

BOILER SAFETY – All of out RT Floor Mounted External Gas Commercial Boilers come with a Gas Leak Detection System as standard

  • When outdoor temperature goes below +4 °C, the boiler automatically protects itself and prevents it and the heating system from freezing.
  • The boiler protects itself, when the temperature of flue gas exceeds the set value during operation,which is  < 70 Degrees C
  • The boiler protects itself should it encounter any unexpected high temperatures within the combustion chamber via a  safety thermostat.
  • Gas Pressure Sensors ensure that these external gas boilers can sustain the gas pressure between the minimum and maximum limits.


External Gas Boiler Larger Sizes, External floor standing condensing gas boiler,large external gas boiler

• Primer hydraulic circuit circulating pump,
• Inlet and return collectors in size according to installed total power,
• Check valve in inlet line and safety valve in return line of the boiler,
• Ball valves in both inlet and return lines of the boilers,
• Balance container with residue, dirt and air separator return collectors in size according to total installed power,
• Gas detector for the gas leakage control,
• Pressure gauge and ball valve in gas line,
• Thermometer in hydraulic circuits,
• Drain trap for each boiler,
• Ventilation grills for the air inlet and outlet,
• Eye bolt for easy transport.

Savings and efficiency

  • Condensing technology
  • Total flame modulation (heating and sanitary)
  • Certified efficiency up to 107%
  • Suitable water flow to the external gas boiler heat exchangers with suitably sized flow and return pipework, and hydraulic separation of the boiler circuit
  • Cascade sequence control and heat exchangers in“rotation” so all boilers have equal aging , and thus expanding the life-cycle of the boiler plant


  • Very quiet in operation
  • Outdoor sensor and climate control options available
  • Easy installation and maintenance
  • Reduced size and weight

Construction quality

  • Modern, innovative and attractive design
  •  Aluminium heat exchangers – Which offers excellent thermal capacity, meaning water can move more slowly around the system and the return water temperatures are cooler, increasing efficiency.
  • Turn down ratio up to 1:10 for the 300 kW model

Ecology & Environmentally Friendly External Gas Boiler

  • Fecralloy fibre premix burner
  • Reduced gas emissions in the atmosphere – With  low CO and NOx

Dimensions of the RT Floor Standing External Gas Boilers

Large External Floor Standing Gas Condensing Boilers Dimensions RT Series

Flexiheat Brochure for External Gas Boilers – Floor Mounted

These three Boilers make up a full range of external gas boilers, that can cover any application. Please remember that by mounting these boilers externally , you will dramatically reduce or eliminate your flueing costs , by locating your external gas boiler in a position that suits you and your site conditions. All of the covers that we do are CE certified, insulated and frost protected, and made from anti Ultra Violet ABS material for the smaller ranges or Anodized Aluminium for the floor standing range. So whatever your application we have the External Gas Boiler to provide the solution to your needs.

For more information on our External Gas Boilers , please don’t hesitate to contact our sales team on 01202 822221 or email us here