After water heating and steam generation air heating in some form or another is the largest market for heating and combustion equipment. It is intended that this web site section provides a brief over-view of the subject.

Information is provided on Air heating energy requirement calculations,

Refer to Fig. AH-1a (for metric units) and Fig. AH-1b (for imperial units).

Information is provided on Make Up Air (general),

Information is provided on Make Up Air heating (combustion quality),

Information is provided on Make Up Air Packaged Heater Units,

Refer to Fig. AH-2a , Fig. AH-2b , Fig. AH-2c , Fig. AH-2d and Fig. AH-2f

Information is provided on Process Air heating (Ovens & Driers),

For illustrations of process air heaters see Fig. AH-3a and Fig. AH-3b ,

For combustion product temperature - excess air graph see Fig. AH-3c

Information is provided on Indirect Fired Air heating,

For illustrations see Fig. AH-4a , Fig. AH-4b , Fig. AH-4d and Fig. AH-4e.

The heating of air with gas burners in industry can be broadly divided into two types of application; industrial process and industrial comfort heating.

The industrial process field, most commonly includes ovens for drying and paint baking. There are of course many other applications, from chemical-curing and bakery ovens to brick drying.

Industrial space or comfort heating includes indirect fired air heater systems and direct or indirect fired air replacement systems.

Air for virtually all types of application can be heated using either direct or indirect fuel firing. Because of practical and economic considerations the majority of industrial process heating systems use the direct fired method.

Industrial space heating systems tend to use indirect firing, although air replacement (make-up air) systems for fuel efficiency and installation cost reasons favour direct firing. The basic difference between direct and indirect firing is that with direct firing the combustion products are mixed with the air being heated, whilst with indirect firing some sort of heat exchanger is required, so that combustion products do not contact the air being heated.

Generally the direct-fired method is preferable because of the simplicity of the equipment and the high thermal efficiencies that can be obtained. In the direct-fired method, the combustion products make contact with the workload. Virtually all of the heat of combustion is available for the process, resulting in efficiencies of up to 100%. This compares very favourably with the efficiency of using steam or hot water coils, or indirect gas or oil fired heat exchanger systems, where efficiencies of between 50% and 80% are normally achieved.

Both direct and indirect fired systems require burner equipment, valves and ancillary controls; however the requirement to have some sort of heat exchanger and the physical size and design of that item results in the indirect fired system being a more expensive installation and involving a higher maintenance cost. When the additional costs and the lower fuel efficiencies of the indirect fired system are fully considered it is easy to understand that direct fired systems are generally preferred and why indirect systems are normally limited to use on applications were possible contamination of the air stream or product cannot be accepted.

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  Air Heating

  Air Heating - (Energy Requirements)
  Make Up Air - (General)
  Make Up Air - (Combustion quality)
  Make Up Air - (Heater Units)
  Process Air Heating - (Ovens & Driers)
  Indirect Fired


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Comtherm Limited accepts no responsibility or liability for the accuracy of information provided on this web-page. technical data and dimensions should be confirmed with the relevant Comtherm Limited Sales or Technical office.