Plain English Meaning

A small fuel-burning heater inside the aircraft that warms cabin air by passing it over a hot metal chamber. The flame and its exhaust stay sealed away from the cabin; only clean, heated air is sent inside.

Full Definition

An aircraft cabin heating system that produces heat by burning a small, controlled amount of aviation fuel inside a sealed combustion chamber. Outside air is drawn across the outside of that chamber, warmed by contact with its hot walls, and then ducted into the cabin. The exhaust gases from the burning fuel are kept entirely separate from the cabin air and are vented overboard. heaters are commonly installed in whose engines do not produce enough waste heat for an exhaust (muff) heater to be practical, such as many aircraft and twins.