Fire that's hot inside cabin (5)
I believe the answer is:
'cabin' is the definition.
(I have seen 'Rough cabin ' mean 'shack' so perhaps 'cabin' could also mean 'shack')
'fire that's hot inside' is the wordplay.
'fire' becomes 'sack' (dismiss someone from their job).
'that's hot' becomes 'h' (abbreviation eg on taps).
'inside' is an insertion indicator.
'sack' going around 'h' is 'SHACK'.
(Other definitions for shack that I've seen before include "grim lodgings" , "building made of wood?" , "Crudely built hut" , "Roughly built hut" , "Crude dwelling" .)