Good as a source of heat, perhaps (3)

I believe the answer is:

gas

'a source of heat perhaps' is the definition.

'good as' is the wordplay.
'good' becomes 'g' (abbreviation).
'g'+'as'='GAS'

(Other definitions for gas that I've seen before include "American fuel" , "Petrol (USA)" , "Hydrogen or methane, say" , "Chatter vapidly" , "Hydrogen possibly" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app