Cabin Air
Most small airplanes rely on fresh air intakes to provide comfort inside the cabin during warm weather. usually, air inlets in the leading edge of the wings direct air to fresh air outlets inside the cabin. The air moves through the vents and into the cabin due to the ram air pressure created by the airplane's forward motion.
Airplanes may also be fitted with an air conditioner. This is not common on small airplanes, however, due to the load an air conditioner places on the engine, which results in reduced airplane performance.
Conveniently, the temperature of the atmosphere drops with increasing altitude. As a result, most airplanes are only uncomfortably warm during taxi, even on the hottest of days.
Cabin Heat
Most small airplanes use a heat exchanger to heat outside air from the engine's exhaust. Air is directed into a shroud, where it is heated by the hot exhaust pipes. From there, the hot air is directed into the cabin.
This method of providing cabin heat should not result in exhaust gases ever coming into contact with air meant for the cabin. The system is designed so that only the heat is provided. However, should even a small exhaust leak form inside this heat exchanger, small amounts of exhaust gasses would be directed into the cabin by the selection of cabin heat. The use of cabin heat is safe, but you should turn off the cabin heat and open fresh air outlets if you smell exhaust gasses or your carbon monoxide detector indicates their presence in the cabin.
During cold weather, cabin heat and cabin air are usually used together to provide the most comfortable temperature inside the cabin. Controls in the cabin provide the ability to select variable amounts of either.
Windshield Defrost
Windshield defrost operates by directing cabin heat through outlets near the windshield, heating the windshield.