Originally Posted by joecaption
Your resoning makes no since, but yes it needs to be insulated in most cases.
Mainly on where you live, where the pipes are located.
well metal conduct more heat than plastic. when i touch a section that has both hot water copper pipe and plastic pipe. the temperature of plastic pipe is barely warm, however the copper pipe at the same section is too hot to touch. so insulation on plastic pipe cost/insulate ratio might not worth it, since it doesn't give out too much heat. however i'm not sure how much i would save if i insulate the plastic pipe.