AFUE (Annual Fuel Utilization Efficiency) ratings are something that every homeowner should learn about and be aware of. AFUE ratings are governmental standard of the measured thermal efficiency of furnaces, boilers, hot water heaters, etc. This is not the only measurement available to determine the energy consumption of any such system, and does not calculate absolutes, but rather calculates the seasonal average of heat loss.
This is not the only means of measuring the efficiency of any given system or product, and differences of opinion exist on which is more useful. This is large a circumstantial aspect, dependent upon what the consumer is actually trying to calculate. The AFUE is best overall for season-to-season estimation, whereas if one is trying to determine the heat lost over the short term, a measure of thermal efficiency is probably more accurate.
Regardless of the measure used, the goal is to be aware of how much energy / heat / fuel is used to perform a given task-the home-heating equivalent of how many miles on a treadmill are required to burn off a piece of birthday cake . However, whereas in exercise we are looking to burn the maximum number of calories per mile, in heating a home, the goal is to use as little fuel possible while providing a maximum output of heat.
One of the best reasons for a home owner to be aware of AFUE standards is that, just like auto emission standards, they have changed as more efficient machinery, equipment and insulating materials have been developed and become available for widespread use. For example, currently boilers (anything manufactured in 1992 or later) must have an AFUE of 80%. Boilers older than this are not held to such a high standard, which means the older one's heating system is, the lower its efficiency.
A lower rating means that one of the heater will require more fuel to heat a given space, and lose more heat that should be going into a home to the air. This will raise a homeowner's heating bills significantly in the winter, or force them to live with a much colder temperature than would be necessary with a more efficient boiler.
While there is a significant initial outlay in replacing an older heating system with a new one, the end results will be substantial savings. A more efficient heater can pay for itself in a disproportionately short time and the savings will be immediately noticed in gas or electric bills. Because of these potential benefits, it is important for every homeowner to be cognizant of the age of their heating system.
The savings will be evident in another fashion as well. Most local utilites will reward the reduced environmental impact of a heating system that has a better AFUE rating and is ENERGY-STARTM rated with rebates. Thus, having a licensed heating contractor install a more efficient heating system will result in more heat for less money, leading to increased comfort in the cold months. Along with the sense of well-being that can be earned from being financially rewarded for acting in an environmentally friendly fashion, upgrading becomes a win-win situation.