Air Heater Basics Part Four: Hot Air Blowers vs. Air Heaters

At its most basic level, an air heater works by passing air across a heated element to elevate the temperature of the air. That hot air can then be used for a variety of applications ranging from heating a space to drying parts and coatings, or from de-flashing plastic components to heating parts in a manufacturing process.
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Recommended reading in this series:

• Air Heater Basics Part One: Air Heaters Defined
• Sizing your Heater and Blower: The Relationship between Air Flow and Temperature
• Air Heater Basics Part Two: Elements
• Understanding Blowers as part of a System
• Air Heater Basics Part Three: Choosing an Air Source

Heater Configuration

​There are many different sizes, shapes, and configurations of heaters which vary in complexity. This article will focus on the difference between a Hot Air Blower and an Air Heater

Hot Air Blowers

​Some heaters on the market package both the air source and heating element into a single tool. These can range from small hand tools with 400W elements to large industrial units with 10kW elements and everything in between. These have the obvious appeal of simplicity and, sometimes, compact design. For some applications these are ideal but in many situations a system designer requires the flexibility of specifying both the heater and air source separately in order to achieve the best possible results.

Air Heaters

Many air heaters provide the heating component only and require an external source of supply air. While this adds a layer of complexity to the heat system design, it also gives the system designer a greater degree of freedom. A heat system can be developed which will provide the exact kilowatts required to deliver the correct volume of air at the correct temperature for the application. This type of “perfect fit” is often not possible with an off the shelf Hot Air Blower.

Choosing the Right Heater

There are several decisions a heat system designer must make in choosing the right air heater.
1. High or Low Volume Air Flow
The application will generally point towards either a high flow (open element) or low flow (fully supported element). A few examples are:

• When high temperatures are required — Fully supported element
• When a large cavity must be filled with hot air — Open element
• When coupled with an air knife for drying applications — Open element

2. On-board Thermocouple
Industrial heaters can be found both with and without an on-board thermocouple. It’s important to give careful consideration to an application’s control needs to avoid paying for more sophistication than is required. You may choose to omit an on-board thermocouple when selecting a heater if:

• The location at which the temperature is important is a distance away from the heater outlet. In these applications, a thermocouple placed in that location should be used rather than a thermocouple in the heater itself.
• An external temperature controller will be used that is not compatible with the on-board thermocouple.
• The accuracy/precision of the on-board thermocouple is not adequate for the application.

3. On-board Temperature Controls
As with the on-board thermocouple, there are sophisticated heaters that also have on-board temperature controls. On-board temperature controls are almost always paired with feedback from an on-board thermocouple. Although the heater itself may be more expensive than one without this capability, there are situations where it is more economical because closed-loop control is possible without any external control components. There are also times when it does not make sense to have this capability, such as:

• An external temperature controller is required as part of the larger process.
• Closed-loop temperature control is not required.
• The critical temperature must be measured at a specific location, not at the heater outlet. This requires a thermocouple at that point of application.
• Very precise temperature control is required. While on-board temperature control usually provides acceptable accuracy, and is a significant upgrade over an open-loop system, external closed loop systems will almost always be more precise and accurate.

4. Compatibility with Air Sources

• Compressed Air
  Compressed air may be the right option if there are severe space constraints or very high system pressure requirements. However, it is generally not recommended due to the high associated energy cost and the chance of contamination by water or oil, which can damage the air heater.
• Blower
  ​To be effective, the appropriate blower must be selected to pair with your air heater. Choosing an ill-sized blower can result in damage or destruction of your air heater, or can result in a poorly performing system. The heater supplier should provide specifications for minimum air flow and maximum operating pressure requirements for the heater. Operating temperature versus air flow information should also be available, if you cannot find this information in the supplier’s literature or website be sure to ask. It is also important to understand how a blower will interact with your heater, as blower output changes when back pressure is applied. If you are not sure which blower to select, the heater supplier should be able to help you choose the most appropriate type for your application. For more information on types and applications for different types of blowers, please see our whitepaper on the topic. 

Many people make the mistake of choosing a heater/blower combination from a catalogue based on maximum flow or temperature values; in reality, there are many factors that influence the correct equipment choice. When you contact your heater supplier they should ask for details of your application to be sure you are choosing the appropriate equipment. If they don’t, we suggest you consider finding an alternate supplier who can ensure that the equipment you purchase is right for your application. 

Continue reading: ​Air Heater Basics Part Five: Sizing a Heater and Blower