AFUE, SEER2 and HSPF2: reading efficiency ratings without the jargon
Efficiency ratings are useful for comparing equipment, but they are only part of the story. Here is what each one measures.
By JBrown Mechanical
Every furnace, air conditioner, and heat pump comes with efficiency numbers. They appear on yellow labels, spec sheets, and quotes, often as a string of letters that is hard to decode. They are worth understanding, because they help you compare equipment fairly. They are also easy to over-read.
AFUE: furnaces and boilers
AFUE stands for Annual Fuel Utilization Efficiency. It is expressed as a percentage and describes how much of the fuel a furnace or boiler burns over a typical season ends up as heat for the home, rather than being lost through venting and other losses.
A higher AFUE means a larger share of the fuel becomes usable heat. Higher-efficiency gas furnaces are typically condensing designs, which capture extra heat from exhaust gases. Condensing equipment has different venting and drainage needs than older furnaces, which matters if you are replacing an older unit.
SEER2: cooling
SEER2 is the Seasonal Energy Efficiency Ratio, updated under a newer testing procedure. It describes how much cooling an air conditioner or heat pump delivers for the electricity it uses over a typical cooling season. Higher numbers indicate more efficient cooling.
You may still see the older SEER rating on older equipment or literature. The two are not directly interchangeable because the test conditions differ, so compare SEER2 with SEER2.
HSPF2: heat pump heating
HSPF2 is the Heating Seasonal Performance Factor, also under the newer test procedure. It describes how efficiently a heat pump heats over a season. As with SEER2, higher is more efficient.
For a Michigan home, it is also worth asking how a heat pump performs at low outdoor temperatures specifically, since a seasonal rating averages across conditions that may be milder than a cold January week.
What ratings do not tell you
Ratings are measured under standard laboratory conditions. They are a fair way to compare one model with another, but your actual results depend on things the label cannot capture:
- Whether the equipment is correctly sized for your home
- The condition and design of your ductwork
- Correct refrigerant charge and airflow at installation
- How well the house holds heat, including insulation and air sealing
- How you set and use the thermostat
A high-rated system installed poorly can perform worse than a modestly rated system installed carefully. Quality installation is consistently identified as one of the biggest factors in real-world performance.
Using ratings sensibly
When you compare quotes, ratings help you see whether you are looking at similar tiers of equipment. They also help explain differences in price and complexity between options. But choose a rating level in the context of the home: how long you plan to stay, how the house is used, and what comfort problems you want to solve.
It is reasonable to ask whoever is quoting the work why they recommend a particular efficiency level and what other changes, such as duct repairs, might matter as much or more.
Be cautious with promises
Be wary of anyone who promises a specific percentage of savings based on a rating alone. Your actual energy use depends on weather, habits, the house, and installation. Ratings are a guide, not a guarantee.
Where to start
If you are weighing equipment and the numbers feel overwhelming, bring the quotes and your questions. We can explain what the ratings mean for your home and what else deserves attention.