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

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

Direct fired gas space heaters – Outputs from 25kW to 90kW

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

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, as the exhaust ventilation or products of combustion are expelled directly into the area.

They are also very popular as a poultry shed heater / breeding shed heater but there must be some level of air exchange in the area. Direct fired heaters can’t be utilised in a tightly sealed spaces, they need air exchange to operate correctly (to feed the combustion process) and safely.

The “FHG” direct fired 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 and are great for temperature sensitive applications. The combustion products are discharged in the space to be heated along with the hot air. Robust technology and extremely high manufacturing quality ensure flawless operation and long service life of these direct fired heaters.

They have high fuel efficiency at 100%, as direct fired heaters turn all of the fuel used into direct heat, thus reducing fuel consumption and operational expenses, but please note they add carbon dioxide and carbon monoxide to the environment of the heating process.

We recommend installing destratification fans with any warm air heating system to force the warm air that rises within the building downward to ground level. Destrat fans may save up to 20% to 30% on energy usage, lowering your heating system’s operating expenses.

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

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

Direct fired gas heater efficiency

These direct fired heaters are gas fired commercial and industrial air heaters that 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 direct fired heaters as frost guards or a frost protection heater.

Using a thermostat, the direct fired heater is then automatically activated, to keep room’s 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, but helps with fuel efficiency.

Their air volume 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 direct fired heater 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 fired 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 these direct fired heaters are “CE” approved and manufactured in the EU.

FHG36-25  –   25 kW output direct fired heaters  – Airflow- 3,000 m³/h – Electrical supply – 230V/ 50Hz

FHG45-40 –   40 kW output direct fired heaters – Airflow- 4,000 m³/h – Electrical supply – 230V/ 50Hz

FHG56-65   –  65 kW output direct fired heaters – Airflow- 7,000 m³/h – Electrical supply – 230V/ 50Hz

FHG56-90  –  90 kW output  direct fired heaters- Airflow- 8,000 m³/h – Electrical supply – 230V/ 50Hz

Technical Data for our “FNG” range of Direct Fired Gas (either LPG or Natural Gas) Heaters

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

Thermal PowerkW4250
Air Volumem³/h3,0004,0007,0008,000
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 direct fired heaters can offer a perfect solution in ensuring a constant , reliable and efficient heat source  for this application


  • Clean and efficient burning – high thermal efficiency
  • Cost effective – lower operating costs
  • Expensive oil spill fines can be avoided and the environment is kept unharmeddirect fired poultry heater gas fired
  • Rapid poultry shed/ farm heating
  • Reliable and dependable fuel source


Every direct fired heater has got a built-in pressure controller.


As standard these direct gas fired hot 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 Gas Air Heaters Brochure 25kw to 90kW Output

Download the Flexiheat Manual for “FHG” direct fired gas heaters natural gas or LPG gas

Direct Fired Gas Warm Air Heaters – Safety Advice

  • If the direct fired 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 tightly sealed spaces 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 or more information on 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.