FAQs on Fan, Duct, Fin & Process Air Heaters

What are fan-assisted process air and duct heaters?

Air heaters' primary purpose is to heat the air in a specific space or area. The space to be heated could be an industrial process, air duct to a larger area, equipment cab, or interior of a house or car.  The design of the duct or forced air heater is dependent on the specific application.

The design of this type of heater is a honeycomb or other fin-type structure that will transfer heat efficiently to the air being forced across the structure.  Electric resistance heaters are embedded inside the fins or honeycomb structure that in turn transfers the heat to the air flowing through.

For process air heaters the fin or honeycomb structure made of aluminum or stainless steel typically will span the inside dimensions of the duct carrying the air to an area targeted for heating.  This creates a very efficient & consistent heat transfer.

There is an extensive variety of heat exchangers arrangement for duct heaters including finned tubular, open coil, honeycomb, triangular, and straight fins.  The configuration depends on the required airflow and each offers different heat transfer characteristics.

What type of electric heating elements are used in air heaters?

The heating elements used in fan heaters or sometimes called finned air heaters have evolved over the years to safer and less complicated solutions.  Electric resistant wires and infrared heaters are still used today but the safer and more durable PTC heaters are quickly becoming the norm.

How do infrared heaters work?

Infrared heaters work by emitting light that warms a surface similar to the sun heating our bodies.  The light must hit the object to be heated.  If infrared is used for forced air heating the light strikes a heat exchanger that has air flowing across it to conduct the heated air to the targeted space.

The heating of moving air in this manner is inefficient compared to other sources of heat.  Manufacturers claim that infrared heat doesn’t take oxygen and humidity from the air.  The most efficient way to use infrared heat is where the light can be directed onto the surface to be heated.

How do electric resistive elements heat air?

The electric element in resistive heaters is a coil of bare wire that current flows through making it glow and creating heat.  Air flowing over these elements pulls the heat from the glowing wire transferring it to the air.

The downside of this type of heating element is anything combustible coming into contact with it will burn, including human hands.  Safety guards are usually in place to prevent accidental contact with combustible materials or humans.

The current flow through the resistive elements needs to be controlled via a switch, circuit breaker, or temperature-controlled loop circuit devices.  The electric resistive wire can be embedded into the aluminum fin structure or heat conductive material for more efficient heat transfer and safety. A temperature sensor is often placed in the outlet airflow to control the heat.

PTC might be the most economical electrical heaters?

PTC, positive temperature coefficient heating elements create heat from current flowing through the ceramic disk.  The disk’s resistance varies with the temperature of the element such that as the temperature increases the resistance increases reducing current flow through the element.

This PTC effect regulates the current and the heat produced automatically without the need for external temperature sensing and control devices.  Each disk is designed for a specific temperature, voltage, and current.

There are several advantages to utilizing PTC  elements.  Multiple disks can be embedded throughout a honeycomb or fin structure for even heating.   The surface temperature won’t ignite combustible materials.  Safety due to self-limiting heating and no required maintenance makes it highly desirable for use in industrial applications.

The ceramic disks are bonded to the aluminum or stainless steel structures for efficient heat transfer.  Their small size and high power ratios make them ideal for smaller applications.  They also come in multiple voltage ratings.

Do electrical heating elements burn oxygen?

Electric resistance heaters, infrared, resistance wire, or PTC do not burn oxygen.  Oxygen is only consumed by an open flame.  None of the electrical devices produce an open flame.  None of the devices will reduce the oxygen in the heated area.

• Infrared heaters heat by light waves that don’t burn oxygen.
• Resistive wire heating heats by the energy given off by exciting electrons, no oxygen.
• PTC ceramic heaters heat by electrical resistance, also no oxygen is involved.
• Gas or wood fires used in heating burn oxygen.

Do electrical heating elements reduce humidity?

Heating air does not reduce the humidity in a space.  Heated air can actually hold more humidity.  As temperature increases, absolute humidity stays constant although relative humidity decreases.

Confused?  The relative humidity is named for its relationship to the temperature in the room.  If moisture stays constant as the temperature rises and can hold more moisture the humidity relative to air temperature goes down.  The actual moisture content stays the same.

In damp climates that contain a lot of moisture, heating a room or electrical panel enclosure raises the dew point and keeps the moisture in the air from forming water molecules.  The water molecules are what forms condensation on cooler surfaces and mold.

Keeping the relative humidity the same in a room as it is heated helps with creature comfort.  During the winter months when homes are often heated the additional moisture in the air will make you feel warmer and more comfortable than in dry conditions.  The additional moisture is a personal choice.

Why does it feel so humid in southern climates in the summer?  The higher temperatures hold more moisture in the air. That additional moisture is only released as the temperature declines.  Hence why we often feel cooler air in rainstorms.  The air has cooled and moisture is released from the air via water vapor or rain.

Manufacturers of electrical enclosures use .heating to control humidity and moisture in outdoor cabinets.  Condensate evaporators and hygrostats are used to maintain a perfect balance in humidity in ATMs, ticket machines, and remote controls for gas and oil installations.

What are fan-assisted heaters?

Manufacturers have created finned or honeycombed heaters with the fan physically attached to the heating components.  The fan, typically on a separate electrical circuit, forces air over the finned structure pulling heat away from the heat exchanger into the air or through the ductwork.

Are air heaters safe?

Electrical air heaters are safer than gas or propane heaters in that there is no flame.  Both fan assisted and unassisted heating components are insulated and their heating elements are protected from coming into contact with combustible materials and humans.

The PTC ceramic heating elements are perhaps the safest because they have built-in temperature limiting capabilities.  They will not overheat and automatically shut off when the desired temperature is reached.  Controlling temperature is important in process heating applications.

What voltage do finned or duct heaters use?

Industrial electric fan heaters requiring higher wattage output come in 120, 230, and even 400V units.  A 12-volt car fan heater is made specifically for automotive voltage systems.

More answers about thermal engineering fans or duct heaters.

Have an industrial air duct heating application? It is best to consult with an experienced thermal engineer for the right solution.  Custom design is available for volume applications. Call and discuss your application with us.