Four ratings, four different questions
Cooling delivered over a standard season compared with the electricity used. Higher is more efficient in that test.
Cooling output compared with electric input at specified test conditions—not a whole-season score.
Heat delivered over a standard Region IV heating season compared with electricity used.
The share of annual fuel energy converted to useful indoor heat in a standard furnace or boiler test.
These are comparison tools, not savings guarantees. Weather, energy rates, thermostat settings, the house, ductwork, backup heat and installation all affect actual operating cost.
Why did SEER become SEER2?
Federal test procedures changed in 2023. The newer SEER2, EER2 and HSPF2 tests use a procedure called Appendix M1; for ducted equipment it includes higher external static pressure to better represent installed conditions. That means an older SEER number and a newer SEER2 number are not the same scale.
The relationship depends on the equipment category and test procedure. Compare current matched-system ratings, not a marketing shortcut such as “old SEER minus X.”
For a Massachusetts heat pump, the seasonal number is not enough
HSPF2 is useful, but it does not by itself tell you how much heat a model can deliver during a cold Massachusetts design day. Also compare its rated capacity and coefficient of performance at low outdoor temperatures, the proposed backup heat, and whether the duct system can deliver the required airflow.
Current ENERGY STAR cold-climate criteria include a COP of at least 1.75 at 5°F and at least 70% of the 47°F heating capacity available at 5°F. That certification is useful evidence—not a promise that every house can eliminate backup heat.
The rating belongs to a matched combination
A condenser does not earn a complete-system rating by itself. The outdoor unit, indoor coil or air handler, and sometimes the furnace and controls form the tested combination. The AHRI reference number is how a certified match can be identified.
“Up to 18 SEER2” describes the best eligible combination in a product family. Your proposed capacity and indoor match may carry a different rating. HVAC PM packages compatible components first, then shows the applicable efficiency—not the highest number from a brochure.
High-rated equipment can still waste energy
ENERGY STAR says improper installation can reduce efficiency by as much as 30%. Oversizing can cause short cycling and weak humidity control. Incorrect airflow or refrigerant charge can reduce performance. Leaky or undersized ducts can keep conditioned air from reaching the rooms that need it.
ENERGY STAR notes that a typical home may lose roughly 20–30% of the air moving through a duct system through leaks and poor connections. That is a national rule of thumb—not a measurement of your house. A duct review or leakage test is what turns the general risk into a real finding.
- Sizing: use the existing tonnage as a clue, then verify the load and the area this system actually serves.
- Airflow: confirm the blower, filter, coil and duct resistance can support the selected system.
- Matching: identify the AHRI-certified outdoor and indoor combination.
- Commissioning: verify charge, temperature response, controls, drain safety and operating sequence.
What does 80% versus 90%+ AFUE change?
An 80% AFUE furnace converts about 80% of the fuel’s test-cycle energy into indoor heat; the remainder leaves mainly through venting and equipment losses. AFUE does not include duct losses or all electrical use. A 90%+ condensing furnace recovers more heat, but the installation changes too.
Converting from a metal-flue furnace usually requires a new approved exhaust route, combustion-air provisions for the selected model, and condensate drainage. A pump, neutralizer or freeze protection may be needed depending on the route and local conditions. If a water heater remains on a shared chimney, its venting must be evaluated after the furnace is removed. See the 80% → 90%+ installation guide →
How to compare proposals without chasing one number
It connects the exact outdoor and indoor equipment to its certified ratings.
For a heat pump, compare delivered capacity, COP and the backup-heat strategy—not HSPF2 alone.
Sizing, ducts, airflow, electrical, venting, condensate, controls and commissioning belong in the proposal.
Its operating cost uses standard assumptions and an average energy price; it is not your future utility bill.
HVAC PM’s Builder starts with the system you have, installation conditions and what you want to improve. It uses efficiency as one part of a complete installed recommendation, then flags what still needs field verification.