So a friend of mine is living in an apartment with central heating but the radiators are removed, so there are just the pipes. He seems to think that if you cut aluminium jar caps and cover the pipes with them, it will increase the surface area of the pipe and therefore heat the room more. The same general idea applies to anything from aluminium, like covering the pipes with beer cans. This is a popular myth around here and I believe that it should either not work at all or the increase would be extremely small, like in the sub 5% range. Can you help me understand the problem and show me how to do the calculations ?