[John123]

You seem knowledgeble about this issue. Do you know how long this "plastic pipe" ban has been in place?

My home is 15 years old and we have a lot of plastic piping under the sinks. It does make it easier for me to clean "U" pipes or replace the leaky pipes.

In your opinion, which piping is more energy efficient for transporting hot water; plastic or copper? :)

[Doomonyou]

My home is 15 years old and we have a lot of plastic piping under the sinks. It does make it easier for me to clean "U" pipes or replace the leaky pipes.

Right. That is on the waste side, still OK, and I agree, ABS or PVC is easier to work with than cast iron.

In your opinion, which piping is more energy efficient for transporting hot water; plastic or copper? :)

I'm no energy expert, but I would say plastic has a higher R-value than copper. Most exposed copper water lines are required to be insulated these days. Check the photo in post #6, those copper pipes should be insulated (Note the hot water heater has a blanket.)

IMO.

[ErnBatavia]

we have a lot of plastic piping under the sinks.

That's because what you see are for drainage only; the pressurized lines coming into your faucets would be copper or galvanized.