Air heaters are used to heat air with forced convection, radiant heat, or resistive heating elements. Forced convection moves air past a heat source with a fan or blower. Radiant heaters radiate heat from coils that contain a heated, circulated media such as oil, hot water, or steam. Resistance air heaters consist of sheaths that surround a resistive heating element. The functional use of these tubular heaters is limited only by available space, maximum sheath temperature, and watt density. Air heaters use a variety of power sources, including electricity, fuel oil, diesel, gasoline, kerosene, natural gas, and propane. Solar heaters and devices that burn wood products are also available. Air heaters with fins provide improved heat dissipation.
Many types of air heaters are available. Examples of forced convection devices include heat torches, fixed electric fan heaters, flued and unflued gas heaters, and slow combustion wood heating. Duct heaters mount in air delivery ducts and supply supplementary heat to delivered air. Strip heaters are flat devices that can be bolted, clamped, or otherwise attached to solid surfaces for freeze protection and humidity control. Enclosure heaters also provide freeze protection and humidity control, along with equipment protection.
Parameters for air heaters include maximum air temperature, maximum air flow, and heating capacity. Maximum air temperature is the maximum temperature of air exiting from the heater. Maximum air flow is the maximum flow of air through the heater. Heating capacity is the wattage which the heater can deliver. In terms of features, air heaters may be corrosion-resistant, explosion-proof, finned, microprocessor-controlled, portable, or UL approved. Products with independent timing controls and an encased coil or grounding wire are also available. Portable heaters are lightweight, handheld, and/or have wheels. Indirect fired heaters include a secondary heat exchanger to separate the breathable air stream from the combustion air stream. Hazardous location heaters are designed for use in places where there is a risk of fire or explosion. Underwriters Laboratories (UL) or other regulatory agencies often rate these devices.