by Ali Kriscenski


A building’s annual operating costs are often at the mercy of external factors such as fuel prices, weather conditions or occupancy levels. While some factors are variable, other components and conditions can be controlled. One of these is the Annual Fuel Utilization Efficiency (AFUE) of your building’s furnace. 


What Is AFUE?

The AFUE rating of your furnace is a tool that helps you understand your system’s energy efficiency. It conveys the amount of energy used (fuel) to create useful thermal heat. It is measured as an annual rating to better reflect the average efficiency throughout seasonal changes.



To calculate the AFUE rating, divide the fuel supplied to the furnace by the amount of heat produced (BTUs).


 A furnace’s efficiency limit is 100%, meaning at 100% it is operating at maximum efficiency — i.e. converting all of the fuel into useful thermal energy. A furnace with an AFUE of 90% has 10% energy waste. An open, outdoor fireplace might have an AFUE closer to 50%.


AFUE and Operating Costs

Fuel efficiency has a direct relationship to operating costs and energy savings. The higher the AFUE of a furnace, the more fuel consumption (and costs) are being utilized efficiently. Furnaces with a lower fuel efficiency produce more waste, which translates into energy loss and wasted money. Within an annual maintenance schedule, it can be useful to consider your energy use, energy efficiency, operating costs and the cost-effectiveness of an equipment repair or upgrade that could improve energy efficiency and overall sustainability.

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Furnace Maintenance for Improved Efficiency

Older heating systems tend to be less efficient than newer equipment. With regular maintenance, these older systems may have retained a consistent AFUE over the equipment’s lifespan. However, devices and components in newer models have advanced equipment efficiency. 


Fortunately, it is possible to retrofit older equipment to increase the AFUE. For example, vent dampers help reduce thermal energy loss through exhaust and intermittent ignition devices lower the amount of fuel used for continuous pilot lights. Devices such as vent dampers and intermittent ignition devices are both fairly small improvements (under $500) that produce long-term energy savings.


Another way to improve energy efficiency is to perform an annual inspection to identify any repairs or maintenance needed within the heating distribution system. Cleaning and repairs to duct work, filters and thermostats can all have an impact on how much energy your furnace uses to create heat. 


Upgrading Your Furnace

Not all older furnaces can be retrofitted with safety and energy improvements. As systems age, even with regular maintenance, components and equipment may need to be replaced in order to obtain the desired AFUE. While older systems typically cap out at 70% efficiency, newer furnaces can be expected to run at 90% – 95% efficiency. Although an upgrade incurs upfront costs, the return on investment can typically be recouped through long-term annual energy savings.



Setting and Meeting Your Energy Efficiency Goals

Whether you are a facilities manager or building owner, the systems that heat and cool your building are central to daily comfort, operations and safety. Understanding the efficiency of your furnace and its AFUE can be a useful part of your overall energy and operating plans. 


As energy efficiency has a direct impact on operating costs, a good first step in planning is to take a deep dive into your operating budget. Check to see how energy costs matchup against similar buildings. Run through maintenance checklists with your staff to reveal any straightforward repairs or upgrades that could improve energy efficiency. Enlist the expertise of an HVAC professional to help identify potential retrofit or replacement opportunities and outline the costs vs. expected ROI. These steps will help you use your equipment ratings, age and efficiency to find untapped energy savings.


Ali Kriscenski was trained in high-performance building design at Boston Architectural College. She has worked with leading architecture and construction firms in NYC and New England and served on the executive team at the Forest Stewardship Council International. She was the managing editor at Inhabitat and has worked pro bono for the Green Building Institute, ISEAL Alliance and Habitat for Humanity.



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