Dictionary of HVAC Efficiency Rating Terms

There a lot of acronyms involved with HVAC. At Aire Central we want to help you understand the different rating methods so you make a more informed purchasing decision when shopping for a new heating or air conditioning system.

SEER – Seasonal Energy Efficiency Ratio

What it measures: Cooling efficiency across a typical season. It’s the total cooling output (in BTUs) divided by the electricity used (in watt-hours) over a standardized set of lab tests.
How to read it: Higher is better. SEER captures part-load performance (how systems run most of the time), so it’s great for comparing overall AC/heat pump cooling efficiency.
Reality check: SEER is a lab rating, your home’s ductwork, airflow, and installation quality can move real-world efficiency up or down.

SEER2 (the newer test)

What it is: A newer standard (since 2023) using tougher test conditions (higher external static pressure) to better reflect real homes.
How to read it: Numbers look a bit lower than legacy SEER for the same equipment because the test is harder. Don’t compare SEER and SEER2 directly – compare SEER2 vs SEER2.

EER – Energy Efficiency Ratio

What it measures: Instantaneous cooling efficiency at a single, fixed set of conditions (typically 95°F outdoor, 80°F indoor, 50% RH).
How to read it: Higher is better. Because it’s tested at high outdoor temperature, EER is useful for judging peak-heat performance.
EER vs. SEER: SEER is seasonal/part-load, EER is single-point/full-load. For the same system, EER will usually be lower than SEER because it’s rated at a tougher (hotter) condition.

EER2

Same idea as EER, but under the updated SEER2/EER2 test protocol with higher static pressure. Again, compare EER2 to EER2, not to legacy EER.

HSPF – Heating Seasonal Performance Factor (for heat pumps)

What it measures: Season-long heating efficiency for heat pumps. It’s total heat delivered (in BTUs) divided by electricity used (in kWh) across a range of outdoor temps.
How to read it: Higher is better. Great for understanding how efficiently a heat pump heats over an entire winter.

HSPF2

The updated test standard that better reflects real-world conditions. As with SEER2/EER2, HSPF2 values are not one-to-one with HSPF, compare within the same scale.

AFUE – Annual Fuel Utilization Efficiency (furnaces & boilers)

What it measures: The percentage of a fuel furnace’s input energy (natural gas, propane, oil) that becomes usable heat over a heating season.
How to read it: Higher is better. An 80% AFUE furnace turns ~80% of its fuel into heat (about 20% is lost); a 95–98% AFUE condensing furnace captures much more heat from exhaust.
Note: Actual results depend on venting, duct/air distribution, and setup quality.

COP — Coefficient of Performance (heat pumps)

What it measures: Instantaneous heating (or cooling) efficiency: heat moved out divided by electric energy in.
How to read it: Higher is better, and values can be >1 (that’s the magic of heat pumps moving heat rather than making it). COP drops in colder weather; a system might be COP ~3 at 47°F but lower at 17°F.
Use case: Great for engineers and energy geeks comparing heat pumps at specific temperatures.

CFM — Cubic Feet per Minute (airflow)

What it measures: The volume of air your system moves through ducts and registers.
Why it matters: Correct airflow is essential for both comfort and efficiency. Too little airflow can kill efficiency, reduce capacity, and stress equipment; too much can be noisy and waste energy.
Rule of thumb: Many designs target about 350–450 CFM per ton of cooling, but the right airflow depends on coil design, humidity goals, and duct static pressure.

BTU & “Ton” – Capacity, not efficiency

BTU (British Thermal Unit): A unit of heat energy. In HVAC, we talk in BTU per hour (BTU/h).
Ton: A convenient way to express cooling capacity. 1 ton = 12,000 BTU/h. A “3-ton” AC provides about 36,000 BTU/h of cooling.
Remember: Capacity (BTU/ton) tells you how much heating/cooling you get; efficiency ratings (SEER2/EER2/HSPF2/AFUE) tell you how much it costs to deliver it.

Manual J Load Calculation

A standardized, detailed method developed by the Air Conditioning Contractors of America (ACCA) to determine the precise heating and cooling needs of a home.

Quick Tips for Homeowners

  1. Compare apples to apples: SEER2 vs SEER2, EER2 vs EER2, HSPF2 vs HSPF2.
  2. Higher isn’t always “best” for you: Pick efficiency levels that match how long you’ll stay in the home, your comfort goals (humidity/quiet), and budget.
  3. Installation quality = everything: Duct design, static pressure, and commissioning can swing real-world efficiency more than a single rating point.
  4. Think whole system: Matched indoor/outdoor units, correct refrigerant charging, proper airflow, and smart controls all raise both comfort and efficiency.

Need help choosing the right rating for your home?

Aire Central will size, design, and commission your system so you actually get the efficiency you’re paying for.
Call (678) 580-1753 for a free, friendly consult.