Air Preheaters

Heat exchangers that preheat air to increase efficiency

Air preheaters take energy from a process stream to heat the air that enters a system. This operation increases the inlet temperature of the air to the process, thus improving the system’s overall efficiency.

What is an air preheater?

In general, a preheater is a heat exchanger that increases the temperature of a gas or liquid before it is fed into another process.

An air preheater does this specifically for air, taking energy from a process stream to heat incoming air elsewhere in the system. By increasing the inlet temperature at which the air enters the process, it improves the overall efficiency of the system.

Air preheaters may be configured as gas to air or liquid to air, depending on the available process streams.


There are a variety of applications for air preheaters. Take a power plant boiler, for example. An air preheater can be utilised to recover heat from the flue gas and increase the heat of the combustion air, making the process more efficient.

Air preheaters are most often used are in the following industries:

As a leading manufacturer for the industrial air preheater market, Sterling Thermal Technology provides services for all of these industries. If you have air preheater needs, contact us today.

Air preheater design considerations

Depending on where excess heat is available from, either a liquid to air or gas to air preheater will be used.

For example, heat may be available from condensate streams in a steam generating process. In this instance, a water to air preheater is appropriate. Alternatively, gases downstream of a combustion process may require further cooling after the main heat recovery has been accomplished. If so, a gas to air preheater is called for.

Depending on the preheater type, there are different technical considerations.

Liquid to air preheaters

For liquid to air preheaters, or condensate preheaters, we use extended surfaces to enhance the heat transfer coefficient of the air. We choose tube material based on an understanding of the corrosion potential from the tube side fluid. Fin and tube pitching depends on the potential for fouling of the surfaces.

Gas to air preheaters

It is a common requirement to use the products of combustion to preheat air. However, the quality and temperature of the gas stream may vary significantly. Therefore, for gas to air preheaters, we potentially have to examine additional factors, including how to bring together the gas and air streams.

Tube expansion on start-up, as well as the diameter of the ducting, may dictate significant aspects of the equipment layout. Any carry over of solids in the gas stream will be a factor in determining the pitch of tubes and the use of an appropriate fouling factor. We might recommend mechanical methods for the removal of solids.

Why partner with Sterling Thermal Technology for air preheaters?

  • Multiple design options: We have a range of design options that we can harness to address the most challenging process requirements. Whether it is considerations of the overall layout, the differential expansion or stream cross-contamination, we have a suitable arrangement to meet the challenge.

  • Cost-effective specifications: We can use plain tube arrangements on either fluid to air or gas to air preheaters where the use of extended surfaces is not an appropriate economic approach.

  • Corrosion-resistant products: Where gas streams are being cooled, there is a risk of corrosion if condensate forms. In that case, we would recommend appropriate materials and advise on the best configuration to minimise that risk.
Air preheater using NEL fin technology, designed and manufactured by Sterling Thermal Technology

Air preheater using NEL fin technology

Air preheater, oil sections

Air preheater, oil sections

Looking for an air preheater manufacturer?

Sterling TT has over 100 years’ experience in the heat exchanger and industrial air preheater market. We work with both original equipment manufacturers and end-users to deliver top-class results based on our customer’s specific needs.

Tell us your requirements and find out what we can do for you: contact us today.

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