Aquire Hydrogen.
The enthalpy of combustion for hydrogen is −286 kJ/mol
2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ (286 kJ/mol)
A little Dangerous so treat like a toxic gas + dry ice.
Use a gas mask and gloves to handle dry ice.
Place a combustiable item under the sub-zero flame and record resaults.
(paper, plastic and wood)