What is the AFUE Rating?
It is a rating that reflects how efficiently a gas furnace converts fuel to energy. An AFUE of 90 means that approximately 90 percent of the fuel is utilized to provide warmth to your home, while the remaining 10 percent escapes as exhaust. You can find the AFUE rating on the yellow EnergyGuide label that is attached to every gas furnace.
What Does AFUE Stand For?
AFUE stands for Annual Fuel Utilization Efficiency.
The higher the AFUE rating, the more efficient the furnace. A furnace with an AFUE rating of 90 is considered very efficient, while a furnace with an AFUE rating of 50 is considered only moderately efficient.
The AFUE rating is helpful because it allows you to compare the efficiency of different furnaces.
The limitation of the AFUE rating of gas furnaces is that it only measures the efficiency of the furnace itself. It does not take into account the losses that occur in the duct system.
For this reason, gas furnaces with an AFUE rating of 90 are not necessarily more efficient than gas furnaces with an AFUE rating of 80. The difference in efficiency is largely due to the design of the duct system.
In order to get the most accurate estimate of how efficient a gas furnace will be in a home, a heating load calculation done should be performed. This calculation takes into account all of the factors that affect how efficiently a furnace will operate in your home, such as the size of the home, the insulation levels, and the type of windows.
How is AFUE Calculated?
The AFUE rating is calculated by dividing the amount of heat output by the amount of fuel input. For example, a furnace that outputs 90,000 British thermal units (BTUs) in an hour while consuming 100,000 BTUs of fuel has an AFUE rating of 90%.
Heat output is calculated by multiplying the amount of airflow (in cubic feet per minute) by the temperature rise. For example, if a furnace produces 500 CFM at a temperature rise of 40 degrees Fahrenheit, it has a heat output of 20,000 BTUs. HVAC profesionals use sensors to determine this.
Fuel input is calculated by multiplying the amount of fuel consumed by the heating value of the fuel. For example, if a furnace consumes 1,000 cubic feet of natural gas per hour and the heating value of natural gas is 100,000 BTUs per cubic foot, the furnace has a fuel input of 100,000 BTUs per hour.
The AFUE rating is not the only measure of a furnace’s efficiency, however. Other factors, such as the amount of heat produced per watt of electricity used and the amount of moisture removed from the air, should also be considered.
Why Does AFUE Matter When Choosing a Furnace?
The AFUE rating is important when choosing a furnace because it tells you how efficiently the furnace converts fuel to heat. A higher AFUE rating means that the furnace is more efficient and will save you money on your energy bills.
However, the AFUE rating does not take into account the losses that occur in the duct system. For this reason, it is important to also consider the size of the home and the type of windows when choosing a furnace. A furnace with a high AFUE rating may not be the most efficient choice for a small home with old, leaky windows.
What is a “Good” AFUE rating?
There is no one “good” AFUE rating. The AFUE rating of a furnace varies depending on the type of fuel it uses. A gas furnace with an AFUE rating of 90% is more efficient than an electric furnace with an AFUE rating of 95%.
It is also important to consider the size of the home when choosing a furnace. A small home will not need as much heat as a large home, so a furnace with a high AFUE rating may not be necessary.
What is an “Efficient” AFUE rating?
An “efficient” AFUE rating is anything above 80%. A furnace with an AFUE rating of 80% or higher is considered efficient. Furnaces with lower AFUE ratings
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