Direct Fired Gas Heaters-Natural or LPG – Suspended – Warm Air Heaters

Direct fired gas heaters – Outputs from 25kW to 120kW

These units are direct fired warm air heaters, which means that they add CO2 from the combustion process into the area being heated. This makes them particularly suitable to greenhouse and poly tent heating, as the plants or crops use the CO2 beneficially.They are also very popular as a poultry shed heater / breeding shed heater.The “FHG” direct fired gas warm air heaters have been developed and certified in compliance with  EN 525:2001 standard and qualified for heating of industrial and agricultural spaces. The function of these heaters is to ensure the temporary or continuous heating of the designated work areas or agricultural spaces. In case of proper use, these direct fired warm air gas heaters guarantee safe and energy saving operation. The combustion products are discharged in the space to be heated along with the warm air.Robust technology and extremely high manufacturing quality ensure flawless operation and long service life

direct fired gas heaters,direct fired natural gas heater,direct gas fired industrial air heaters,direct gas fired air heaters

Characteristics of our Direct Gas Fired Industrial Air Heaters – FHG Version

  • High efficiency – 100% efficiency with these direct fired gas heaters
  • Low NOx and CO emissions
  • Stainless steel body – ensuring long product life cycle
  • Thermostatic control – Set your desired temperature and the operation of the heater is fully automatic

Direct fired gas heater efficiency

These direct gas fired industrial air heaters have a high efficiency of 100% and you can use a room thermostat to closely control the temperature thus saving energy.

Thanks to the thermal control, you can also use the heaters as frost guards or a frost protection heater.Using a thermostat, the heater is then automatically activated, to keep rooms free from frost or to avoid excessive drops in temperature. The short heat recovery time reduces temperature fluctuations, promoting a natural growing environment, and the fan provides circulation to reduce dead spots in the greenhouse, reducing high moisture areas that promote mould.

Direct Gas Fired Air Heaters – A Complete Range  

Firstly our “FHG” range of suspended gas fired direct heaters  – the power output goes from 16 kW to 90 kW,with 4 direct fired gas heaters units the range. The “FHG” range of direct gas fired industrial air heaters are equipped with a temperature control unit located on the side of the control panel in the direction of the air fan. The temperature control range is between 0 to 40 degrees Centigrade.The automatic control of temperature is carried out through the automatic switching on and off of the appliance in accordance with the air temperature in the room and the set temperature value, as all models are provided with thermostatic socket and plug – the thermostat is an optional extra.

Their air flow has increased and the noise level has reduced thanks to the new fans with sickle-shaped blades. The new electronic board has air flow control and three-attempts restart system (in compliance with the regulation EN298:2012). The 90kW model has the optional function of switching on just the ventilator / fan and in this way it works as an air circulator.All of this range of direct heaters are certified and tested by IMQ , which is an organisation independent of the party selling and manufacturing the product and carries out all tests on the product necessary to verify conformity to legal safety and reliability requirements.Also the heaters are “CE” approved and manufactured in the EU.

FHG36-25  –   25 kW output model – Airflow- 1,000 m³/h – Electrical supply – 230V/ 50Hz

FHG45-40 –   40 kW output model – Airflow- 2,000 m³/h – Electrical supply – 230V/ 50Hz

FHG56-65   –  65 kW output model – Airflow- 5,000 m³/h – Electrical supply – 230V/ 50Hz

FHG56-90  –  90 kW output model – Airflow- 7,000 m³/h – Electrical supply – 230V/ 50Hz

 Technical Data for our “FNG” range of Direct Fired Gas (either LPG or Natural Gas*) Heaters * Must be specified at time of order

direct fired gas heaters; direct fired natural gas heater; direct gas fired industrial air heaters; direct gas fired air heaters;

Thermal PowerkW25406590
Air Flowm³/h2,6004,0006,2007,000
Gas ConsumptionLPGkg/h1.822.915.096.55
Natural Gaskg/h2.383.815.918.58
Gas PressureLPGbar               0.030(G30)
bar               0.037(G31)
Natural Gasbar              0.020(G20)
Electrical SupplySingle Phase – 230V 50Hz
Electrical Powerw180180370550

Poultry Heating with Natural and LPG Gas

A reliable heat supply is essential to all businesses. But for poultry farmers it really can be a matter of life and death as birds thrive on consistent levels of heat – especially during the rearing season. The Flexiheat range of gas air heaters can offer a perfect solution in ensuring a constant , reliable and efficient heat source  for this application


  • Clean and efficient burning
  • Cost effective
  • Expensive oil spill fines can be avoided and the environment is kept unharmed
  • Rapid poultry shed/ farm heating
  • Reliable and dependable fuel source


Every heater has got a built-in pressure controller.


As standard these direct gas fired air heaters have three safety devices –

Airflow sensor – Should the fan fail, the direct fired warm air heater would immediately stop.
Ionization flame monitoring – The gas supply stops immediately as soon as the gas flame would go out.
Temperature limiter – the built-in protection thermostat prevents the unit from overheating.

The gas flame is constantly monitored by thermo elements and ionization electrode, making these direct fired warm air heaters a very safe warm air heater.

These Direct Fired Warm Air Heaters can be operated in three modes:


In this case, no heating is required in the room, but the fan is operated to ensure either air change or air circulation. Set the ON/OFF switch, which is the lower one on the side of the control cabinet, to ON position. Set the upper “Heating-Ventilation” – “Heating” switch to “Heating-Ventilation” position. Set the thermostat to the minimum.If set this way, the heater will only ventilate the room.


The switches have to be set in the same way as it is done with the “ventilation only” mode, the only difference is that the thermostat has to be set to the desired temperature. When the temperature in the room drops below the set value, heating is started. After the room’s temperature is increased to the value set on the thermostat, the heater will perform ventilation only.


Set the ON/OFF switch on the control cabinet to ON position. Set the upper two position switch to the “Heating” position. If set this way, the appliance heats up the room to the temperature set on the thermostat, and when the desired value is reached, both heating and ventilation will stop

Download Direct Fired Air Heater Manual

New for 2019 the “FHRTG” range of direct gas fired air heaters

The “FHRTG” are a range of direct gas fired heaters designed for poultry houses/farms or greenhouses. With its modulating premix burner, the power capacity can ramp down to 30% which allows for important energy savings and reduced fuel costs, be it for natural gas or propane gas that you use as your preferred fuel.

direct gas fired industrial air heaters , FHRTG Range from Flexiheat UK

These Direct Gas Air Heater works with natural gas (G20/G25) or propane (G31). The range includes 3 models from 60 kW to 120 kW and two versions, either a stainless steel or a galvanized steel body. The galvanized steel body gas fired heater is available only as a ON/OFF direct fired gas heater – whilst the stainless-steel body gas fired heater is available as a modulating direct fired gas heater.

Product advantages                                     Customer benefits

  • Modulating premix gas burner               Output modulation from 100% to 30%
  • Direct Heat                                                  100 % efficiency
  • High air flow rate                                       Good heat distribution
  • Removable panels                                      Easy to clean
  • Small and compact                                     More usable space in the area being heated
  • Integrated control board                           Automatic control (ON/OFF)
    with ambient sensor (standard)
  • Integrated control board                          Remote control (modulation)
    with 0-10 volt signal (option)

Another great benefit of this range of direct fired natural gas heaters or direct fired propane heaters (depending on your chosen gas) is that they feature a combustion air connection, meaning you can bring clean fresh air to the burner. This helps prevent any problems with the heater as no dust or debris is drawn into the combustion chamber, which can foul the combustion process and cause a shut down or damage to the heater.

direct fired natural gas heater,direct gas fired air heaters,direct gas fired industrial air heaters

Download the Flexiheat “FHRTG” Direct Fired Gas Air Heaters Brochure

Direct Fired Gas Warm Air Heaters – Safety Advice
  • If the heater is used in a closed space, adequate amount of ventilation air has to be supplied
  • The appliance should not be exposed to the following strong effects: wind, high pressure water jet, rain or dripping water
  • As dust is flammable, the appliance should not be used in areas with high dust concentration.
  • Keep these gas heaters away from flammable materials such as fuels, solvents and combustible fluids.
  • These direct fired gas heaters are equipped with a thermostat, therefore, the heaters can start operating at any time depending on the temperature settings.
  • It is strictly PROHIBITED to use these direct gas heaters in rooms that are used by humans for sleeping or are continuously occupied.
Direct Gas Fired Air Heaters for Sale in the UK & Ireland 

If you require any further assistance with our Direct Gas Fired Air Heaters / Direct Gas Fired Industrial Air Heaters , that are a great solution for poultry and pig warm air heating systems, not to mention any greenhouse heating requirements , then please click here to contact us via email or call us direct on 01202 822221.