Base board heater - what type of fitting and best way to replace

[John McAllister]

What is the above fitting called? 

I want to replace the fitting with something new like a shark bite. 

I had a plumber look at it and he didn’t know which was surprising. 

[Matt Devincenzo]

Is that orange piece a plastic pipe of some sort? It looks like a compression union similar to what would be used on a fridge ice maker line.