The most economical solution for heating and cooling most buildings is passive solar design — using the elements of the building to collect and store solar energy for heating and using climate resources for natural cooling.

Passive solar systems use energy from the sun and climate resources to provide both heating, cooling, and ventilation. They do not rely on auxiliary energy sources to function. Because there are no pumps or controls, they will work even if the power is off. They are simple and relatively low in cost. They combine collection and storage. They have a long life and need little maintenance. They use energy-inexpensive materials. They can be built and installed by the regular construction trades without special equipment.

Water wall passive solar buildings are usually the most attractive type of passive solar home. The key element for a passive solar home is thermal mass — and water provides this mass at a lower cost than either concrete or phase change salts.