Hot planet — a place that’s warming (6)
I believe the answer is:
hearth
'a place that's warming' is the definition.
(fireplace)
'hot planet' is the wordplay.
'hot' becomes 'h' (abbreviation, eg on taps).
'planet' becomes 'earth' (Earth is an example).
'h'+'earth'='HEARTH'
(Other definitions for hearth that I've seen before include "fireside feature" , "Open fireplace" , "suitable place for a fire" , "a warm, welcoming place" , "part of furnace" .)