Correct use of abbreviation I am writing a scientific paper and I introduced the abbreviaton:
Underfloor heating system (UFH). 

Can I now use UFH to talk about the underfloor heating system or do I have to write: UFH system?

I am asking because I have many pictures that are difficult to change were I use UFH (and it should stand for underfloor heating system).
Your abbreviation is a bit misleading because you left out the initial of system, but you want it to mean system.

If you want to write just the abbreviation, I suggest you to use UFHS instead, to comprise system.