Aircraft Heater Systems: Exhaust Heating and Combustion Heating
An aircraft heating system is integral for the safe operation of an aircraft. In the duration of its flight cycle, an aircraft will encounter volatile temperature changes and a heating system can help ensure all aircraft components maintain their necessary temperature for efficient and reliable operation. Two heating systems frequently utilized in aviation are exhaust heaters and combustion heaters. The systems share one similarity— both utilize the heating of ambient air or ram air. Let’s take a look at how heater systems work.
Exhaust heaters are most commonly seen on smaller, single-engine aircraft. The unit is installed around part of the engine’s exhaust system and is sometimes referred to as an exhaust shroud heater. An exhaust manifold delivers warm exhaust into the metal shroud. Ram air is also brought into the shroud from outside of the aircraft. The air is warmed by the exhaust, then routed through a heater valve to the cabin. In some models, the air is routed to the carburetor as well. Exhaust is then transferred to an outlet.
This type of heater doesn’t need an independent electrical system or engine power to operate, making it efficient in a small aircraft. However, this system is hazardous in the event of failures or defects within its hardware— a small crack in the shroud or exhaust manifold has the potential to leak lethal levels of carbon monoxide into the cabin. This system requires rigorous maintenance efforts to keep it operating safely.
Combustion heaters are seen on various aircraft sizes. A combustion system operates independently from the engine and only relies on engine fuel from the main fuel system. The system incorporates a ventilating air system, fuel system, and ignition system to heat various components of an aircraft. In order to heat incoming air from the ventilating system, the combustion unit integrates an independent combustion system within a shroud in a heater unit, where fuel and air are mixed and ignited within an inner chamber.
Air intended for combustion is provided by a blower, which pulls air from outside the aircraft and ensures the air is pressurized to the correct specifications. Ram air is collected when the aircraft is grounded, through a ventilating air fan. The ram air is circulated around the combustion chamber and outer shroud, allowing it to heat through convection. Following this process, the heated air is then directed to the cabin. Exhaust from the same process is expelled from the aircraft.
A combustion unit is extremely versatile, which is why it is used on a variety of aircraft. Most are controlled and monitored by a pilot through a cabin heat switch and thermostat and incorporate various redundant safety features. These might include an overheat switch or duct limit.