When cold water needs to be stored to supply an indirect system of cold water, or to feed a system of domestic hot water i.e. an open vented cylinder, the water is stored in a cistern, usually located within the roof space. The cold water storage cistern should have a minimum capacity of 100 litres. If the cistern is also to act as a feed cistern for the hot water supply as well as the indirect system of cold water then it should have a minimum capacity of 230 litres. Cold distribution pipes from the storage tank should be connected so that the lowest point of the water outlet is a minimum of 30mm above the base of the cistern. This is to prevent sediment passing into the pipework. Connections of feed pipes to the hot water system should be at least 25mm above the cold distribution pipes. This will minimise the risk of scolding should the cistern run dry.
Feed and Expansion Tanks
The F&E cistern or feed and expansion cistern is smaller than the cold water storage tank. This is used to supply the water to the open vented heating system i.e. the boiler and radiators. The F&E tank allows the expansion of the hot water within the heating system to vent correctly via a vent pipe which is terminated through the cistern lid and into the tank itself.
Cold Water Storage and F&E Tanks
The Supply float valve should be fitted as high as possible to maintain an air gap and prevent back-siphonage. Overflow pipes should have a minimum internal diameter of 19mm and in all cases be greater in size than the supply pipe. To prevent the ingress of insects, a tight fitting lid must be provided. Where a vent pipe passes through the lid, the pipe must be sleeved. Overflow pipes should also incorporate a filter or screen. Finally the whole installation (cisterns and pipework) should be insulated to prevent freezing.