Pipes often transport water that is substantially warmer or cooler than the air or material around the pipe. High-performance pipe insulation is particularly important since heat loss or gain is greater when there is a large difference in temperature of the water in the pipe and the temperature of the air or material around the pipe. The rate of heat transfer (loss or gain) is greater when the temperature difference is greater. Water heaters typically produce water that is around 135○F, but pipes may pass through areas ranging in temperature from 0○F to 70○F. The big difference in temperature results in great heat loss when pipes are uninsulated or under-insulated.
For example, uninsulated or poorly insulated hot water pipes running through a cold attic, crawlspace, or basement will lose more heat in those areas than when running through the warmer walls within the home. Sometimes these pipes lose so much heat that the water is barely warm enough for a shower by the time it gets to the bathroom.
Even when the temperature difference is not great, the heat loss can be substantial. For example, hot water pipes running through walls in a heated home may be only twice as hot as the air in the home (135○ F versus 68○ F), but the water can still lose much of its heat before it reaches your shower if it runs through uninsulated or poorly insulated hot water lines. This is especially true if the pipes carry hot water a long distance.
Pipe insulation comes in sizes common for pipes and ducts and is made from a wide variety of materials with varying degrees of flexibility and resistance to heat flow. Low-emissivity surfaces are either built-in or can be added for additional performance by reducing heat transfer by radiation.