What Is a Steam Air Heater?

A Steam Air Heater (also known as a Steam Heating Coil or Finned Tube Steam Air Heater) is an indirect heat exchange device that uses steam as the heat source to raise the temperature of air.

Basic Working Principle

• Steam flows inside tubes

• Air flows outside the tubes

• Heat is transferred through the tube wall and fins

• Steam condenses and is discharged via a condensate outlet

Steam and air never come into direct contact
This is a classic steam-to-air indirect heat exchanger

Typical Construction of a Steam Air Heater

Steam air heaters used in industrial drying systems typically consist of:

• Carbon steel or stainless steel tubes

• Aluminum or steel fins to increase heat transfer area

• Steam inlet and condensate outlet headers

• Flanged or bolted connections

• Integrated condensate drainage system

This configuration is widely applied in paper machine hood (campana) air supply systems, coating lines, and industrial dryers.

What Is an Air Preheater (APH)?

An Air Preheater (APH) is a heat exchanger that uses flue gas or exhaust gas as the heat source to preheat combustion air.

Typical Characteristics of an Air Preheater

• Heat source: Flue gas / exhaust gas

• Application: Boilers and combustion systems

• Purpose: Improve thermal efficiency and reduce fuel consumption

• Common types:

  • Rotary air preheater

  • Tubular air preheater

  • Plate air preheater

Air preheaters do not use steam and do not produce condensate.

Steam Air Heater vs Air Preheater: Key Differences

If steam is the heat source, the equipment is not an air preheater.

Typical Applications in the Paper Industry

In paper manufacturing, steam air heaters are commonly used in:

• Paper machine hood (PM Hood) air heating systems

• Drying section air supply

• Moisture profile control

• Energy-efficient hot air generation

Steam pressure is usually low to medium (e.g., ~3 bar), and the equipment is designed for stable, controlled air heating, not for boiler exhaust heat recovery.

Why a Steam Air Heater Should Never Be Called an Air Preheater

Incorrect terminology can cause serious technical and contractual risks, including:

1. Incorrect classification as boiler auxiliary equipment

2. Application of inappropriate boiler or flue gas standards

3. Misinterpretation under pressure equipment regulations

4. Expanded and unintended performance liabilities

For technical documents, contracts, and tenders, the correct designation should always be:

Steam Air Heater (Finned Tube Type)

And not:

• Air Preheater

• APH

Recommended Terminology 

Correct Terms

• Steam Air Heater

• Steam Air Heating Coil

• Finned Tube Steam Air Heater

Terms to Avoid

• Air Preheater

• APH

• Flue Gas Air Heater

Conclusion

A Steam Air Heater is not an Air Preheater.

It is an indirect steam-to-air heat exchanger designed for industrial air heating applications such as paper machine drying systems.
Its heat source, structure, system position, and regulatory attributes are fundamentally different from those of an air preheater used in boiler systems.

Correct classification is essential—not only for engineering accuracy, but also for risk control, contract clarity, and regulatory compliance.