Because air-based systems produce heat earlier and later in the day, solar air heaters may produce more usable energy over a longer time period.
Air in the solar collectors cannot freeze in the winter, and small cracks in the collectors or piping are not problematic. But air is a less efficient than liquid for transferring heat.
Air space heating systems are usually room air heaters, which directly heat individual rooms. A fan pulls air from the room into the collector. The air is heated as it travels through the collector, and is then blown back into the room. There are two ways to mount a solar air heater:
- roof-mounted room heaters need ducts to transport air from the collector to the room
- wall-mounted room heaters are placed on a south-facing wall, with holes cut through the wall to allow the air to pass through to the room