A combustion efficiency test performed on a boiler using fuel oil has indicated that the stack temperature is 700°F and the CO₂ content is 15 percent.

a. Determine the excess combustion air and the boiler efficiency.

b. If the fuel-air ratio is adjusted (so that the O₂ level is only 4 percent and the stack temperature is 400°F), determine the new boiler efficiency and the new CO₂ content.

c. Determine the payback period and cost-effectiveness (d = 5 percent over 15 years) of installing a full metering kit with O2 trim control that costs $30,000. The boiler uses 400,000 gallons of fuel oil per year. The cost of fuel is $1.75/gallon.

d. In fact, the auditor is not sure if oil No. 2 or No. 6 is used! If you want to be conservative in terms of payback period estimation, what fuel type would you use?