Fuel for the grate (8)
I believe the answer is:
firewood
'fuel for the grate' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for firewood that I've seen before include "Logs etc for fuel" , "Substance for burning" , "Tinder" , "Kindling for 17 across" , "Fuel from trees" .)