One common and cost-effective approach for passive solar heating is direct-gain, which relies on south-facing windows to bring solar energy directly into a house. That sunlight is absorbed by materials in the house (floor, walls, furniture, etc.), which warm up, store some of that heat, and re-radiate it back into the room.

In effect, the house itself serves as the solar collector and heat-storage system. The key to success is to provide the right amount of south-facing glass area and to have adequate thermal mass.

With direct-gain, there are no fans or pumps to move heated air or water around. The systems are silent, trouble-free, and easy to maintain by washing windows and, in some cases, opening and closing window blinds to adjust incoming solar gain.

The thermal storage function is most effective with high-mass materials, such as tile or concrete floors, fireplaces with brick or stone facings, and tinted plaster walls. (

Full story.