A guide to direct fired heating units

Where air is extracted from a building either for process or environmental reasons a supply of heated replacement air is required to balance the system and maintain comfort. If make-up air is not provided the extract system will perform inefficiently at reduced capacity and a negative pressure will be created. This results in cold air being drawn in around the perimeter of the building and causing cold spots and unpleasant draughts. 

For new installations the supply of heated make up air can often provide the required ventilation without the need to install additional extract units. Where matching extract is required this can be integrated in the same unit to supply both input and exhaust with the option of heat recovery from the extract air.

Direct gas firing provides a highly efficient method of providing heated replacement air with thermal efficiencies of 100% (based on NCV) and fully modulating burner control with up to 20:1 turndown ratio.

Variable air volume or air recirculation units allow systems to be matched to constantly changing extract rates or to provide full space heating in applications where reduced winter ventilation rates are required.

In heating mode the new Stokvis Econo-Air units provide controlled amounts of fresh air to slightly pressurise the building and the supply air temperature is constantly monitored and adjusted via a fully modulating burner control to optimise the heat input to match the precise building requirements.  Close control of the air discharge temperature virtually eliminates heat stratification, whilst slight building pressurisation ensures very even distribution both laterally and vertically over large areas, eliminating the requirement for extensive ductwork distribution. The amount of fresh air automatically adjusts to meet the ventilation requirements of the space. 

The units provide the ideal solution to large areas with variable occupancy or industrial and commercial heating applications where ventilation rates may change throughout the day. In summer mode the units provide 100% fresh air with the large primary air volumes providing improved air change rates for optimum free cooling. Optional evaporative cooling modules may also be added.

Features and benefits

  • High efficiency for reduced operating costs
  • Fully modulating burner with high turn down ratio (up to 20:1)
  • Close control with rapid response to temperature changes
  • Low maintenance costs
  • Improved indoor air quality
  • Summer fresh air for free cooling
  • Alternative model options allows systems to be tailored to suit a wide range of applications
  • Horizontal or vertical units
  • Indoor or fully weather proofed outdoor units
  • Optional evaporative cooling can be added


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