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Last edited 16 Feb 2021
National Calculation Methodology (NCM) modelling guide (for buildings other than dwellings in England) 2013 edition, published by the Department for Communities and Local Government (DCLG), defines the ‘HWS (Hot Water Service) deadleg length’ as the:
‘Length of the draw-off pipe to the outlet in the space (only used for zones where the water is drawn off). Used to determine the additional volume of water to be heated because the cold water in the deadleg has to be drawn off before hot water is obtained. Assumes that HWS circulation maintains hot water up to the boundary of the zone, or that the pipe runs from circulation or storage vessel within the zone.’
Climate Emergency Design Guide: How new buildings can meet UK climate change targets, published by the London Energy Transformation Initiative (LETI) in January 2020, defines dead leg as:
‘The length of pipe to the outlet in a hot water system. When the outlet is not in use the hot water in this pipe loses its heat so when next used there is a time delay before fully hot water is again available at the outlet. This represents an inefficiency of the heat system.’
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