IN ORDER TO HEAT RECOVERY FROM GAS HEATER EXHAUST, A SIMPLE NATURAL COOLING SYSTEM HAS BEEN DESIGNED AND FABRICATED WHICH COULD REDUCE THE EXHAUST GAS TEMPERATURE FROM 230 C TO 60 C. AS A CONSEQUENCE THE HEAT EFFICIENCY OF THIS COMBINED SYSTEM HAS BEEN INCREASED TO 87% WHICH HAS BEEN CALCULATED BY A THERMODYNAMICS-CHEMICAL MODEL