There are 2 taps below, the main pipe goes to the left, there is a heating radiator in the room, which tap is the right one to close if it’s hot?

   
There are 2 taps below, the main pipe goes to the left, there is a heating radiator in the room, which tap is the right one to close if it’s hot? - My, Plumbing, Installation of heating systems, Heating, Heating battery, Tap, Need advice, The photo

v20221217