Inline heaters instantly heat fluids that are passed through the device. Upon exiting the heater, the fluids are consumed for their intended use and are not re-circulated. Inline heaters are usually electric and feature a high-output heat source. They do not provide enough heat to maintain temperature in a closed system, but impart enough heat to a fluid for immediate use. Specifications for in-line heaters include heater type, application, fuel or energy source, sleeve or sheath material, insulation options, and element or emitter type. Maximum temperature, maximum air flow, heating capacity, power requirements, and induction heater outputs are also important parameters to consider.

There are many different types of inline heaters. Choices include air heaters, band heaters, coil heaters and cable heaters, cartridge heaters, cast-in heaters, ceramic fiber heaters, circulation heaters, drum heaters, duct heaters, enclosure heaters, and flexible heaters. Forced air heaters, heat torches, immersion heaters, induction heaters, and infrared heaters are also available. In addition, inline heaters may include over-the-side heaters, radiant flat panel heaters, radiant reflective process heaters, radiant heater elements, radiators, room heaters or space heaters, steam injection heaters, strip heaters, tubular heaters, and water heaters.  

Inline heaters may be portable or fixed and are used in showers, hot tubs, laboratories, cleaning equipment, and steam cleaners. Applications include annealing and heat treating, curing and tempering, drying, melting, gas or vapor heating, clean water heating, process water heating, and high-purity water heating. Inline heaters are also used to heat high-purity waters, lightweight oils and degreasing solutions, heavy weight oils, medium weight oils, mild corrosive solutions, severe corrosive solutions, caustic solutions, and liquid paraffin. 

There are many different fuel sources for inline heaters. Fuel-source choices include electric; diesel, fuel oil, gasoline, and kerosene; hot water and steam; natural gas and propane; solar; waste oil, and wood or pellets. Specific types of inline heaters such as drum heaters, cable or coil heaters, ceramic fiber heaters, and immersion or circulation heaters.       

Sleeve or sheath material and insulation type are important specifications to consider when selecting inline heaters. There are many different types of sleeve materials. Choices include aluminum, brass, copper, iron, and proprietary nickel alloys; ceramic foil, fluoropolymers, natural rubber, and synthetic rubber; and steel and stainless steel. Some in-line heaters have ceramic, mica, or mineral insulation. Others use magnesium oxide or fiberglass. Inline heaters with no insulation are also available.