Hot Water Pipe Insulation
All hot water pipe that is accessible should be insulated. Even if it is in a heated space, the water temperature is MUCH higher than the space temperature, and the loss is 100% during the non-space heating months.
The best residential insulation available is made from foam for a specific size of pipe. It should be securely taped in place to prevent air gaps and to keep it from falling off.
The vertical cold water pipe nearest the water heater should also be insulated. During times of no water usage, the cold water pipe becomes just as hot as the hot water pipe from thermal syphoning (hot water circulating out of the tank and up the pipes by convection).
Insulating all of the cold water pipe can stop condensation and summer ‘sweating’ of cold water lines that causes water dripping onto surfaces below the pipes.