ᐅ When are expansion joints necessary?

Hello,
I am aware of the principle that with copper piping for heating systems (which should be the standard), an expansion joint must be installed every 10 m (33 feet) of pipe length. That sounds logical and I have seen it done before. My question is: Is there a standard, manufacturer’s guideline, or similar regulation that requires this? In other words, is it recommended practice or a mandatory rule? I would appreciate knowledgeable answers.

Copper pipes? Who still does that nowadays??

The HVAC installer. What should I choose then?

Copper is no longer used. Nowadays, it’s mostly plastic, or I believe some still use stainless steel.

For heating pipes?? For drinking water, definitely, but heating? Are you sure?

Could it be that you are misunderstanding each other? One is talking about the pipes directly at the heating unit, and the other about the pipes in the floor. Here, at least, it is common for the pipes at the heating unit to be made of copper, while those in the floor are plastic tubes.