Many variations of systems are used for both solar space heating and service hot water production. The basic configuration is similar to the solar water heating systems outlined in Sections 5.2.1–5.2.3. When used for both space and hot water production, this system allows independent control of the solar collector-storage and storage-auxiliary-load loops because solar-heated water can be added to storage at the same time that hot water is removed from storage to meet building loads. Usually, a bypass is provided around the storage tank to avoid heating the storage tank, which can be of considerable size, with auxiliary energy. This is examined in more detail in Section 6.3.3.