Here is SEER2, HSPF2, AFUE explained in one pass. SEER2 is cooling efficiency for an air conditioner or heat pump. HSPF2 is heating efficiency for a heat pump. AFUE is the percentage of fuel a furnace turns into heat. Higher is better on all three. A 16 SEER2 system sits above both the federal minimum and the ENERGY STAR heat pump level. Whether a 96 AFUE furnace is worth its premium depends on your climate and your house, not the label.
One boundary before the numbers. This article is about reading a quote. Installing, charging or adjusting this equipment is licensed work. Refrigerant handling requires EPA Section 608 certification, and gas piping, venting and electrical connections belong to a licensed HVAC contractor working under your local permit rules. If your home has a fuel-burning furnace, it should also have working carbon monoxide alarms, and any furnace swap that changes the venting should be inspected.
SEER2, HSPF2, AFUE explained side by side
Most quotes print these three numbers in a row with no explanation. This table is the short version. The federal minimums come from the U.S. Department of Energy (DOE) standards that took effect on January 1, 2023. The ENERGY STAR levels come from the EPA's current criteria pages, which we read on September 23, 2026.
| Rating | What it measures | Found on | Federal minimum (typical case) | ENERGY STAR level |
|---|---|---|---|---|
| SEER2 | Cooling delivered per watt-hour of electricity over a season | Central AC, heat pumps | 13.4 (North AC) to 14.3 (split heat pump, and smaller AC in the South) | 15.2 for heat pumps |
| EER2 | Cooling efficiency at one hot, steady condition | Central AC, heat pumps | Required in the Southwest only | 11.0 for split heat pumps |
| HSPF2 | Heating delivered per watt-hour over a season | Heat pumps only | 7.5 (split heat pump) | 7.8 (split heat pump) |
| AFUE | Share of fuel that becomes heat over a year | Gas and oil furnaces, boilers | 80% (standard indoor gas furnace) | 97% gas (U.S. North), 95% gas (U.S. South) |
SEER2 and HSPF2 are ratios. AFUE is a percentage. They cannot be compared with each other, only with the same rating on another quote.
What the "2" changed, and why your old unit's number looks bigger
In 2023, DOE switched to a new test procedure, known as appendix M1. The new test is designed to reflect how a system performs once it is installed and pushing air through real ductwork, so the same equipment now scores lower than it did under the old test. The equipment did not get worse. The test got stricter.
That matters when you compare a new quote with the sticker on your old condenser. DOE's FAQ on the 2023 central air conditioner and heat pump standards, which we read on September 23, 2026, warns that the new and old ratings are similar but not directly comparable, so a SEER number and a SEER2 number should not be read side by side.
So a 16 SEER label on a unit from 2015 and a 16 SEER2 on a new quote are not the same thing: the SEER2 figure came from the stricter test. If a quote lists plain "SEER" for new equipment, ask whether that is a typo or old paperwork.
SEER2: is 16 a lot?
For most homes, yes. A 16 SEER2 system clears the federal floor in every region and clears the 15.2 SEER2 level ENERGY STAR sets for heat pumps. It is a solid efficiency tier, not the top of the market.
The floor depends on where you live. For split-system central air conditioners, DOE's 2023 standards set:
- North: 13.4 SEER2.
- Southeast: 14.3 SEER2 for systems under 45,000 Btu per hour (about 3.75 tons), and 13.8 SEER2 at 45,000 Btu per hour and above.
- Southwest: the same SEER2 floors as the Southeast, plus a minimum EER2. For most split systems that is 11.7 EER2 under 45,000 Btu per hour and 11.2 EER2 at or above it, with a lower EER2 floor for units rated 15.2 SEER2 or higher.
Split-system heat pumps follow one national standard: 14.3 SEER2 and 7.5 HSPF2. Single-package heat pumps are held to 13.4 SEER2 and 6.7 HSPF2.
One detail catches people out. In the North, the rule follows the date a unit was manufactured. In the Southeast and Southwest, it follows the date it is installed, so an older-stock air conditioner that misses the southern floor cannot legally go in.
Which region you are in
DOE's regional enforcement page defines the Southwest as Arizona, California, Nevada and New Mexico. The Southeast is Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, the District of Columbia and the U.S. territories. Every other state is in the North.
The split exists because hot, dry places spend long hours at peak heat, which is why the Southwest adds EER2, a steady hot-day rating, on top of SEER2, a season-long average. If you live in Phoenix or Las Vegas, ask for the EER2 figure by name. It tells you more about a 110-degree afternoon than SEER2 does.
DOE also says it is illegal for a contractor to install an air conditioner that misses the regional standard in the Southeast or Southwest, and it takes reports at EnergyEfficiencyEnforcement@doe.gov or 202-287-6997. Rules and contacts can change, so confirm the current details on DOE's live pages before you rely on them.
HSPF2: the heat pump number, and the two cold-climate numbers to ask for
HSPF2 is the heating half of a heat pump's rating. A split heat pump must reach 7.5 HSPF2 to be sold. The ENERGY STAR heat pump key product criteria, which we read on September 23, 2026, set 7.8 HSPF2, 15.2 SEER2 and 11.0 EER2 for a split system.
Here is the limit of HSPF2. It is calculated for one reference climate, not yours. A heat pump can post a good HSPF2 and still lose much of its output on a 5-degree morning. If you live where winter bites, two more numbers matter more than HSPF2:
- COP at 5°F: how much heat the unit delivers per unit of electricity at 5 degrees. ENERGY STAR's cold-climate designation requires 1.75 or higher.
- Capacity at 5°F: how much of its rated heating output the unit still delivers at 5 degrees, compared with 47 degrees. The cold-climate designation requires at least 70 percent.
The same page sets cold-climate HSPF2 at 8.1 or higher for ducted split systems and 8.5 or higher for ductless ones. If a quote for a cold region shows only SEER2 and HSPF2, ask for the 5°F figures in writing.
AFUE: is 96 worth the premium over 80?
AFUE is the simplest of the three. A 96 AFUE furnace turns 96 of every 100 units of fuel into heat in the lab test. An 80 AFUE furnace turns 80 into heat and sends the rest up the vent. The federal minimum for a standard indoor gas furnace is 80 percent. Furnaces rated around 90 percent and up are condensing furnaces: they pull extra heat out of the exhaust, which produces water that needs a drain and usually needs a different vent pipe.
Whether 96 pays for itself in your home depends on how cold your winters are, what you pay for gas, how much heat your house loses, how long you plan to stay, and whether the switch needs new venting. No public source gives a payback figure for your house, so we will not give one. Ask for both options priced on the same scope, venting included.
One useful fact: ENERGY STAR's furnace criteria, read September 23, 2026, set 97 percent AFUE for gas furnaces in the U.S. North and 95 percent in the U.S. South. A 96 AFUE furnace qualifies in the South and falls short in the North.
The 2028 furnace rule is not settled
In 2023, DOE finalized a 95 percent AFUE standard for non-weatherized gas furnaces and mobile home furnaces, with compliance set for late 2028. As of September 2026, the rule is back in litigation after the Supreme Court sent the challenge back to the appeals court in June 2026, and DOE has taken public comment on a gas industry petition to delay the date. If a salesperson uses 2028 as the reason to buy now, check the rule's status on DOE's live pages first.
The rating belongs to a matched system, not a box
This is the part most rating explainers skip. A SEER2 or HSPF2 figure is certified for a specific combination: the outdoor unit, the indoor coil or air handler, and sometimes the furnace it sits on. Swap one piece and the rating on the brochure may no longer apply.
The industry record for this is the AHRI certificate, issued through the AHRI Directory of Certified Product Performance. Each certified combination has an AHRI reference number. Ask the installer to put that number on the quote, along with the model numbers of every component. Then the SEER2, EER2 and HSPF2 on the quote can be checked against a record, not just a brochure.
This also protects you when two quotes look alike. Two "16 SEER2" quotes may use different indoor coils, and only one combination may actually be certified at 16. ENERGY STAR's program rules say its split-system ratings must match the levels reported to DOE, so a certified match is the number to trust. For a gas furnace, the AFUE sits on the furnace itself, so the model number is enough.
What the label cannot tell you
A rating is a lab result under fixed conditions. Your bill is set by the whole house. Three things the label cannot see:
Leaky ducts. Every rating is measured at the equipment. If supply ducts in the attic leak, part of that efficient output heats or cools the attic. A higher SEER2 does not fix a hole in a duct.
A leaky, underinsulated envelope. A tighter house needs less heating and cooling, which can mean smaller equipment. A DIY home energy audit shows where your house loses heat, and a blower door test puts a number on how leaky it is. Our guide to where the air leaks actually are covers the sealing, and the climate-zone answer on attic insulation depth covers the attic.
Sizing. An oversized system can carry a high rating and still run in short bursts that waste energy and leave the air damp. Ask how the size was chosen. A room-by-room load calculation (Manual J) is the standard method; "same as the old one" is not.
Doing the envelope work before a replacement is not always possible. When it is, the equipment you buy after may be smaller.
Five questions to put to the installer
Take these to every quote so the numbers line up:
- What is the AHRI reference number for this exact combination? That ties SEER2, EER2 and HSPF2 to a certified match.
- Is every rating on this quote SEER2 and HSPF2, not the older SEER and HSPF? Mixed metrics make quotes look closer or further apart than they are.
- In the Southwest, what is the EER2? In cold regions, what are the COP and capacity at 5°F?
- For a furnace upgrade to 90 percent or higher, what venting and drain work is included, and who handles the permit? If the old furnace shared a chimney with a gas water heater, ask how the water heater will vent safely once it is alone.
- How was the system sized? Ask for the load calculation, not a rule of thumb.
A contractor who answers all five in writing is making a quote you can compare. The work itself stays with them and your local inspector.
FAQ
Is 16 SEER2 good?
Yes, for most homes. It is above the federal minimum in every region (13.4 to 14.3 SEER2 depending on region, size and type) and above the 15.2 SEER2 that ENERGY STAR sets for heat pumps. Higher tiers exist, but ducts, insulation and correct sizing often matter more than the last few points.
How do I convert SEER to SEER2?
There is no exact formula. DOE says the old and new ratings are similar but not directly comparable, so compare new quotes in SEER2 only.
Does a gas furnace have a SEER2 rating?
No. A gas furnace is rated by AFUE. If the quote pairs a furnace with a central air conditioner, the SEER2 belongs to the air conditioner and its matched indoor coil. A heat pump carries SEER2 and HSPF2 because it both cools and heats.
What is a good HSPF2 for a cold climate?
HSPF2 alone does not answer it. ENERGY STAR's cold-climate designation asks for 8.1 HSPF2 or more for a ducted split system and 8.5 for a ductless one, plus a COP of at least 1.75 at 5°F and at least 70 percent of rated capacity at 5°F. Ask for the 5°F figures by name.