Solar space heating systems are similar to solar water heating systems, but generally involve more solar collectors, larger storage units, and a more sophisticated design. These heating systems can use a non-toxic liquid, water, or air as the heat-transfer medium from the solar collector. The heated liquid or air is then circulated throughout the building or home to provide space heating. Another solar space heating technology uses transpired solar collectors along a building’s exterior south-facing wall. The perforations in these collectors allow air to pass through and be heated. This solar-heated air is then channeled into the building’s ventilation system.