Emit, as heat (7)
I believe the answer is:
radiate
'emit as heat' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for radiate that I've seen before include "Travel from centre in all directions" , "Beam brightly, spread heat" , "broadcast" , "Spread (eg heat) out from centre" , "Shine" .)