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Why Your HVAC System’s Efficiency Rating Only Kind of Matters

Serving Families Throughout Dallas
old ripped ductwork

When looking for an HVAC system replacement, you might be tempted to choose the one that the salesperson tells you has the best efficiency rating. They’ll talk about how high the AFUE and SEER are, and you’ll nod and get the general gist, but you might wonder: does a higher efficiency rating mean I’ll actually save money like they say I will?

The answer goes a little beyond a simple yes or no, but don’t worry: it isn’t complicated. Below, we’ll break down what HVAC system efficiency ratings mean and why they are not the only factor when it comes to how much energy your system uses.


A furnace’s efficiency is measured by its AFUE (Annual Fuel Utilization Efficiency). The Department of Energy defines AFUE as “the ratio of annual heat output of the furnace or boiler compared to the total annual fossil fuel energy consumed by a furnace or boiler.” To put it another way, the AFUE ratio helps you get an idea of how efficiently the furnace converts the energy in its fuel to heat throughout one “typical year.”

What is a good AFUE ratio?

Generally speaking, the higher the number, the more efficient the furnace. For example, if a furnace has an AFUE of 80, it will convert 80% of its fuel into usable heat while wasting the remaining 20%. A furnace with an AFUE of 90 will convert 90% of its fuel into usable heat while wasting only 10%.

The current federal minimum AFUE is 80% for new systems. However, a furnace must have an AFUE of 90% or above to be considered “high-efficiency.”


An air conditioner or heat pump’s efficiency is measured by its SEER (Seasonal Energy Efficiency Ratio). The Department of Energy defines SEER as “the relative amount of energy needed to provide a specific cooling output.” In simpler terms, a higher SEER AC uses less energy to cool your home than a lower SEER AC.

What is a good SEER?

Similar to AFUE, the higher the number, the more efficient the air conditioner. All new systems manufactured after January 1, 2015 must have a minimum SEER of 14. Although this sounds like a low standard compared to SEERs of 21 and 22, it actually isn’t when you consider that many old air conditioners still in use only have a SEER of 8. Coming from that, an upgrade to a SEER 14 or 16 will very likely make a marked difference in your energy bills… as long as the factors we’re about to discuss don’t intervene.


If you've ever shopped for a new air conditioning system or heater, you've probably noticed how higher AFUE and SEER seem to correlate with higher price tags. After all, the more efficient the system is, the more money it can save you. The truth is your system can have the highest efficiency ratings in the world, but those ratings won't mean as much when external factors are making your system work harder and use more energy.

Below are some of the most common factors that make HVAC systems less efficient.

Wrong Equipment Size

With HVAC systems, it’s critical that you not only take into account the efficiency rating but also what capacity (size) is recommended for your home based on its size, layout, and climate zone. This is one of the reasons why getting a quote over the phone typically doesn’t work out. An HVAC professional should visit your home, inspect it, and learn about your current heating and cooling issues to provide you with the best system options to meet your needs.

Sloppy Installation

A new HVAC system is one of the biggest purchases you will ever make for your home: you don’t want the installation crew to do anything that will cost you more in the long run. However, to get the job done in a hurry and increase profit margins, many installers will use subpar materials and cut corners. Before investing in a system replacement, take time to find a reputable company who will put your best interests first and complete an installation the right way.

Ductwork in Need of Sealing or Replacing

Your ductwork carries air from your HVAC units throughout the rest of your home, but if it’s full of gaps and holes, a lot of that air will end up inside your walls and attic before it ever reaches you. As a result, your HVAC system will need to work harder and run for longer cycles to make your home comfortable. If your system isn’t performing as efficiently as it used to, rather than replacing it, you might be better off sealing or replacing your ductwork.

Inadequate Insulation and Air Leaks Around the House

Sometimes the amount of energy your HVAC system uses isn’t even it’s fault. Your home might have outdated insulation or air leaks that make heating and cooling the inside a struggle. If you haven’t already, you can start lowering your energy costs by air sealing your home.

Skipped Maintenance and Dust Buildup

Dust and lack of maintenance are two of the top causes of HVAC system breakdowns and decreased efficiency. Keep in mind that your system’s AFUE and SEER aren’t fixed numbers that stay with your system forever, regardless of how it’s treated or how old it gets. Without routine maintenance to keep your system in tip-top shape, it’s going to “age” faster in a lot of ways and need more energy to maintain your desired temperatures.


While AFUE and SEER are something to consider when looking for an HVAC system replacement, you don’t want to overlook the other factors that could impact the system’s efficiency.

At Rescue Air and Plumbing, we provide quality maintenance, repairs, and replacements for heating and cooling systems that ensure your equipment will run safely and efficiently. Call us today at (972) 201-3253 or contact us online to schedule your appointment with our HVAC experts in the DFW Metroplex.