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Furnace afue efficiency ratings explained
AFUE, or Annual Fuel Utilization Efficiency, is a thermal efficiency measure used to determine the average operating efficiency of natural gas and propane appliances. The indication of the level of furnace efficiency is given by the AFUE rating. As per the US Department of Energy, an AFUE rating of 78% or more for a new furnace is considered to be minimal but acceptable.
AFUE is a ratio of useful energy output to energy input. So, an AFUE efficiency level of 78% would signify that for every 100 units of energy input, 78 units of useful energy (heat) is produced. The rest gets dissipated in the combustion process.
This means a higher AFUE rating indicates greater energy efficiency of any particular furnace. AFUE is an important measure of federal compliance and energy consumption.
For you, this means that if you purchase a 100,000 Btu furnace that is 80% efficient, that furnace will generate 80,000 Btu’s of heat.
The standard test for measurement of AFUE for residential furnaces is subject to the ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers) Standard 103.
Why is AFUE even more important than thermal efficiency?
For any combustion heating system, such as furnaces, AFUE is extremely important when measuring seasonal or annual energy comsumption of an appliance because it represents the absolute efficiency of that device during the period in question.
In comparison, thermal efficiency focuses on the measure of steady-state, peak level efficiency. An AFUE rating is usually lower than the thermal efficiency of a furnace and tells you how efficiently the furnace has converted the input energy into usable heat during that entire season or year.
It has been mandated by the Federal Trade Commission that manufacturers should display the AFUE ratings of their furnaces on both the manual and body of the furnace itself so that consumers can easily compare the true energy efficiency between different models.
Electric furnaces have a very high AFUE rating since there is hardly any loss of efficiency through a flue or due to a combustion process. However, overall, electricity is the least efficient form of heat due to the high cost of each unit of electrical power consumed.
Should you replace your old furnace or retrofit it with new parts?
Older furnaces have an AFUE rating between 56- 75%. However, new furnaces can easily reach 95% plus. While the initial investment of replacing an old furnace can be substantial, now is the time to consider the long term energy saving benefits of a 95% efficient furnace.
Considering a furnace installation?
Contact Royal Comfort to discuss your options and for a free, detailed quote today at 765-653-8802