Hello, longtime hvac tech/electrician in the industry here.
We have a 14 unit apartment complex that was rehabbed by us 5 years ago with all new hvac equipment for each apartment.
The local utility was to provide natural gas service so we piped everything for that day.In the meantime all furnaces/boilers/ H W tanks were converted to LP.
We finally have the natural gas switchover scheduled for next week and I have all the conversion kits to convert back to natural gas.

My question is : do I need to purge the lines of lp before introducing the natural gas(after the conversions of course)?

My initial reaction would be no but a couple of local hvac guys said the 2 gases might not get along well. So I would be better off purging the lp before introducing the natural gas. I can do that but it would consume a lot more time.
I googled the question on the internet but didn't get a single hit.
Thanks , Bob