Fellow adjusts rate of radiator (6)
I believe the answer is:
heater
'radiator' is the definition.
(I've seen this before)
'fellow adjusts rate' is the wordplay.
'fellow' becomes 'he' ('he' refers to a man).
'adjusts' indicates anagramming the letters (I've seen 'adjusting' mean this).
'rate' anagrammed gives 'ater'.
'he'+'ater'='HEATER'
'of' acts as a link.
(Other definitions for heater that I've seen before include "Source of warmth; gun" , "Radiator" , "Room warmer" , "fire" , "Warming device" .)