This is the 143rd most frequent Catalan word.
fan
The Catalan word "fan" means "they do" or "they make."
Here, 'fan' is used as part of an expression, indicating that the flags create or bring an effect, emphasizing a characteristic.
Aquelles banderes fan molt color.
Those flags bring a lot of color.
In this context, 'fan' conveys the sense of causing a sensation, specifically the heat emission from the radiators.
Quina calor que fan aquests radiadors!
How hot these radiators feel!
In this sentence, 'fan' is the third person plural of the verb 'fer', meaning 'to do' or 'to make' in English. It denotes performing an action.