The installation of any unvented hot water storage system must comply with the current building regulations and approved document G3. The system must also be installed in accordance with the water regulations giving due care and attention to the design requirements of BS6700:2006 and BS EN 806-1:2000. Consideration should also be given to whether a direct cylinder is connected to an off-peak tariff, if so, the larger of the two capacities should be considered.