In the never ending pursuit of increasing energy efficiency, we decided to insulate all the copper piping coming off of our boiler. I also had an ulterior motive of keeping my shop from overheating this winter.
The pex piping is not too bad in terms of its heat transmittance but all the iron and copper piping just radiates the heat from the hot water. (Of course you can build a simple radiator of iron or copper pipe so that makes sense…)
It was fun to install the insulation around all the valves and take offs, but it should a difference.
When we installed the pex we had also debated insulating it by since we fished a lot of it through closed walls that was not an option and in the basement it was nice to loose a little heat to temper the basement temperature. All & all it looses a lot less heat then the large uninsulated iron pipe that we replaced. I would love to someday to compare the old system’s gas bills to our current redone, zoned, and now insulated system (Of course we demo’ed the old system as soon as we bought the house so we would have to get the bills from the old owners…).