Direct Versus Indirect Fired Heater

Direct fired and indirect fired heaters.

Direct versus indirect fired heater.

Temperature control of an indirect fired heater is not as precise as a direct fired heater as it often under or overshoots the desired temperature by a few degrees. Both types heat the air and work to keep the work area at a comfortable temperature. Indirect fired means that the air is heated indirectly. Learn more about the construction drying options that are available to you.

These types of water heaters are traditionally the most energy efficient. An indirect storage tank is heated through the boiler this requires your boiler to get up to temperature to heat the water properly. Built in thermostats almost all indirect fired heaters use a thermostat. Below is a diagram of a direct fired air heater.

However there are some cases where an indirect fired heater is the better choice. Indirect fired heaters emit 100 clean and dry air and can be used in tightly sealed spaces. Indirect fired heaters also have lower turndown ratios than direct fired heaters resulting in less ability to vary the heat output unless additional heat exchangers are added to improve turndown. Direct fired air heaters are typically less expensive and more efficient than indirect fired units as direct firing units converts nearly 100 of the combustion gases used to hot air.

Direct gas fired units provide higher energy efficiency than indirect units as well as steam heating coils heat pumps high efficiency hot water boilers and even electrical resistance heaters. A direct fired water heater can be heated by propane oil or natural gas and has its own burner. They are more cost effective to install than their indirect counterparts and offer better freeze protection. There are two main choices of heater types for propane heater rentals.

The two most common sources are direct and indirect fired heaters. Can operate in tightly sealed spaces indirect fired heaters do not release carbon dioxide into the space. Some negative aspects about indirect fired heaters are. Third the indirect fired air heater has a thermal efficiency lower than that of a direct fired burner where a direct fired burner is 100 efficient because it combusts directly into the process air an indirect fired heater is typically in the range of 90 to 95 depending on the heat recovery equipment installed to boost the thermal efficiency.

Direct fired heaters can operate in areas with temperatures as low as 30 degrees fahrenheit. However each heater works best in different situations and each has distinct benefits.