National Oilheat Research Alliance 17 relative efficiencies of the average new furnace or standard space-heating-only boiler. Boilers or furnaces made before 1985 do not have AFUEs, so comparing a new boiler or furnace to a much older boiler cannot be done with AFUE. AFUE also does not apply to water heaters that may also be used for heating. And the overall efficiency of a boiler that provides heat and hot water is not accurately measured by AFUE. Heating System Annual Efficiency Heating System Annual Efficiency is the true efficiency of the system. It is the difference between the number of BTUs the customer bought and the number of BTUs they use to heat the building and domestic hot water. It involves all of the energy losses and system interactions measured over the course of the year. It is a function of the gallons of oil used, the temperature of the outside air, solar gain, exposure to wind, the temperature of the inside of the building, the number of occupants and their lifestyle, as well as the amount and temperature of the domestic hot water they used. Unfortunately, there is no standard way to measure the heating system efficiency and each building has a different efficiency. Combustion Efficiency vs. AFUE vs. Annual Heating System Efficiency For years technicians have measured Steady State Combustion Efficiency and used that number to characterize the heating efficiency. It is like highway mileage for a car. The engine is warmed up and the car is cruising down the interstate in high gear. Heating System Annual Efficiency is more like city mileage, with stop and go traffic and idling at red lights. The problem in helping our customers save fuel is that Combustion Efficiency does not factor in all of the losses of the heating system. A unit with a combustion efficiency of 81 percent will be much less efficient and if we could measure AFUE on that unit it might be in the 60s or lower. But if a customer compares 81 to an AFUE of 87, he will not understand how much better off he would be if his equipment were upgraded. Technicians must understand Annual Heating System Efficiency (city mileage) and all the factors that go into efficiency. The NORA Fuel Savings Analysis Calculator is a step in really understanding the true efficiency of the unit, Figure 7. Brookhaven National Laboratory, New York State Energy Research and Development Authority and NORA have developed a way to predict the actual savings for replacing an old boiler or furnace. It is called the Fuel Savings Analysis Calculator. NORA has created a video to explain how to download and use the Calculator. Go to noraweb.org and watch video 14. This calculator is always being improved, so make sure you use the latest version. Figure 7 NORA Fuel Savings Analysis Calculator
NORA Advanced Efficiency
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