Stop heating the sky. Calculate the value of energy lost through your exhaust stacks.
Industrial boilers typically exhaust gases at 200°C to 300°C. By installing an Economizer (a heat exchanger), you can transfer this energy to the incoming boiler feed water.
The calculation follows the thermodynamic principle: Q = m * Cp * ΔT. Even dropping the exhaust temperature by 50°C can result in 3-5% fuel savings, which translates to tens of thousands of dollars annually for large facilities.