On another thread I think I worked out that there is little point in insulating domestic hot water pipes unless you have a circulatory system. Cold water pipes should be insulated to avoid condensation.   I've been wondering about UFH manifold feed and return pipes and did some calculations I thought were worth sharing:   I adapted the pipe insulation spreadsheet from the CheGuide.com. The table shows the amount of heat lost in the feed/return pipes. 'Recovery Factor' r