Many variaties of systems can be used for both solar space heating and domestic hot water production. The basic configurations are similar to the solar water heating systems outlined in Sections 5.2.1 and 5.2.2. When used for both space and hot water production and because solar-heated water can be added to storage at the same time that hot water is removed from storage to meet building loads, the system allows independent control of the solar collector-storage and storage-auxiliary-load loops. Usually, a bypass is provided around the storage tank to avoid heating the storage tank, which can be of considerable size, with auxiliary energy.