Gas transported heat by two directions (6)
I believe the answer is:
ethane
'gas' is the definition.
(ethane is a gas)
'transported heat by two directions' is the wordplay.
'two directions' means two substitutions for 'direction'.
'transported' indicates anagramming the letters.
'by' means one lot of letters go next to another.
'direction' becomes 'N' (N is an example).
'direction' becomes 'e' (E is an example).
'heat'+'n'='heatn'
'heatn' anagrammed gives 'ethan'.
'ethan'+'e'='ETHANE'
(Other definitions for ethane that I've seen before include "Compound" , "Chemical" , "Flammable hydrocarbon" , "Flammable gas; eat hen (anagram)" , "Athene (anag.); a colourless gas" .)