AFUE stands for Annual Fuel Utilization Efficiency. The fuel in this case being natural gas. Althought electricity is also used for the operation of the furnace blower and inducer motor, when it comes to AFUE we are only referring to the source of fuel that is used to generate heat.
Given that the AFUE is an efficiency term, the AFUE of a gas furnace is rated from a scale of 0 to 100% gas consumption efficiency. Today in Toronto, any furnace with an AFUE of 94%, is considered a high-efficiency furnace – based on Canadian government regulations. This used to be at 90% followed by 92%, previously.
What do you think the AFUE of your furnace is? Although, this number might not be readily available, you could always calculate it based on information that should be supplied on the furnace sticker – usually inside the furnace, meaning that you have to open the furnace front door to get this info. The AFUE is the OUTPUT heating power/INPUT heating power. The INPUT and OUTPUT values are always displayed on the furnace sticker. For a 20 to 30 year old Toronto furnace, you are usually looking at around 70% AFUE. Please do remember that the AFUE, depending on the quality of the furnace and the manner in which it has been maintained throughout the years, will slowly decline over the years. So, for instance, if a 25 year old furnace is rated to have an AFUE of 70%, its true efficiency is probably at around 60% after 25 years of hard work. This value can be far less depending on the furnace maintenance record.
If you have a furnace that is about 20 years old or older, its AFUE is probably around 60% at the present moment- which means that for every dollar you are paying to heat your home, only 60 cents is used towards actually heating your home. The other 40 cents is absolutely wasted. So when you replace the furnace with – say an Infinity Carrier model 59MN7A which has an AFUE of 98.5%, you will only waste 1.5 cents as compared to 40 cents which will save you 38.5 cents out of every dollar you pay to heat your home.