Air Heater Basics Part Five: Sizing a Heater and Blower

5/25/2017

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.

Recommended reading in this series:

Sizing a Heater and Blower

The main variable to consider when sizing the heater is the power–or watts–required for the application. To properly size a blower, the two main variables are pressure and flow. More information about pressure and flow can be found in our article. The choices of heater and blower are interrelated in several ways. Below is an overview of the considerations necessary to select the correct match.

Heater Considerations

Temperatures required in the process
Every heater has a maximum rated operating temperature; however, this temperature is not attainable at all flow rates. Be sure that your heater has enough power (kW) to reach the target operating temperature at your desired flow rate. A heater supplier should be able to provide you with a flow versus temperature chart for a heater which will help you determine which model is right for your application.
Size, shape and composition of objects to be heated
The type and amount of material to be heated, the start temperature and final temperature required, and the heating time available must all be considered to determine how much power a heater must have for an application. See our article for a more in-depth look at how to calculate power requirements based on materials being heated.
Environment, losses, and inefficiencies
The surrounding environment must also be taken into consideration when designing a system. For example, the volume of air in a chamber, any losses to the surrounding environment, as well as the material of a chamber walls must be compensated for with extra watts.
Available voltage and amps
Practical constraints can also limit the size of heater. Limited amperage or voltage availability can cap the watts for a heaters.

Blower Considerations (type and size)

Size of chamber
When an air heater is used to supply an oven or heat tunnel, the blower must be sized appropriately to not only fill the chamber with air but to facilitate an appropriate amount of air exchanges to ensure a uniform temperature is maintained. A general rule of thumb used for heat tunnels is to allow for 10 exchanges a minute. This volume exchange will help determine the volumetric flow (CFM, litres/minute, etc.) required from the blower.
Type of heater
Open element or fully supported element heaters have different flow characteristics which will impact blower selection. A centrifugal blower is more suitable for an open element heater and a regenerative blower for a fully supported element heater. A heater will also specify a minimum flow rate, which the blower must be capable of meeting at operating pressure.

These are only an example of criteria that might be needed when sizing a system. It is strongly recommended that if you are not familiar with designing thermal systems that you consult with your heater supplier to confirm any heater and blower selections.

Conclusion

Many people make the mistake of choosing a heater/blower combination from a catalogue based on the specified 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.