Shopping for a new furnace, air conditioner, or heat pump means running straight into a wall of acronyms: AFUE, SEER2, HSPF2, and a “high-efficiency” sticker on everything. It is easy to nod along and let the numbers blur. But these ratings are not marketing fluff. They are the closest thing you have to a fuel-economy label for your home comfort, and understanding them helps you avoid both overpaying and under-buying.
Here is what each one really means, and, more importantly, what it does to your bill.
AFUE: how efficient your furnace is
AFUE stands for Annual Fuel Utilization Efficiency, and it is simple once you strip the jargon: it is the percentage of the fuel your furnace burns that actually becomes heat in your home. The rest goes up the flue.
- An 80% AFUE furnace turns 80 cents of every gas dollar into heat and loses 20 cents.
- A 96% AFUE furnace loses only about 4 cents on the dollar.
In a mild climate, that gap might not matter much. In Northwest Indiana, where your furnace runs hard from roughly October into April, it adds up season after season. That is the core reason high-efficiency furnaces are popular here: the long heating season gives the efficiency time to pay you back.
The catch: high-efficiency (90%+) furnaces vent differently and cost more to install. Whether the extra up-front cost is worth it comes down to how long you plan to stay and how you use heat, which is part of what an honest installation estimate should walk you through. For the full picture on what a furnace costs, see our Northwest Indiana furnace price guide.
SEER2: how efficient your air conditioner is
Where AFUE measures heating, SEER2 measures cooling. It stands for Seasonal Energy Efficiency Ratio (version 2), and the rule is easy: higher is more efficient. A higher-SEER2 air conditioner or heat pump delivers the same cooling using less electricity.
The “2” matters. In 2023 the federal testing procedure was updated to better reflect real-world conditions like the static pressure of actual duct systems. So a SEER2 number reads slightly lower than the old SEER number for the very same equipment. When you compare units, make sure you are comparing SEER2 to SEER2, not an old SEER brochure against a new SEER2 one, or the newer unit will look worse than it is.
For our summers, a mid-to-high SEER2 unit is usually the sweet spot for most homes. Chasing the absolute highest number only pays off if you cool aggressively and stay in the home long enough. If your AC struggles in July, though, the fix may not be a bigger number at all, it may be sizing or ductwork, which we cover in Why Your AC Can’t Keep Up in a Heat Wave.
HSPF2: how efficient a heat pump is at heating
If you are considering a heat pump, you will meet a third rating: HSPF2 (Heating Seasonal Performance Factor, version 2). It measures how efficiently a heat pump heats. Again, higher is better.
Heat pumps are rated on both SEER2 (for the cooling they do in summer) and HSPF2 (for the heating they do the rest of the year), because a heat pump does both jobs. If you are weighing a heat pump against a gas furnace for our winters, we wrote a balanced, local breakdown in Heat Pump vs. Furnace in Northwest Indiana.
The number that beats all the numbers: proper installation
Here is the part the brochures leave out. A top-rated, high-efficiency system will not deliver its rated efficiency if it is:
- Sized wrong for the home (too big is as bad as too small),
- Installed sloppily, or
- Feeding leaky ductwork that dumps conditioned air into your attic.
That last one is huge. You can buy a 96% furnace and still lose 25 to 40% of its output through duct leaks you cannot see. That is why Aeroseal duct sealing is often the highest-return upgrade we do, and why we always look at the whole system, not just the box with the shiny rating. We dug into the comfort side of this in Why Your Home Is Never Evenly Comfortable.
Where to sanity-check the numbers
The ENERGY STAR program is a neutral, trustworthy place to see which efficiency levels earn recognition and what they mean. Their central AC and heating product pages spell out current thresholds in plain terms, and the yellow EnergyGuide label on any unit gives you an estimated annual operating cost you can compare across models.
The bottom line for a NWI home
- AFUE = furnace efficiency. Higher wastes less fuel; valuable in our long heating season.
- SEER2 = cooling efficiency. Higher uses less electricity; compare SEER2 to SEER2 only.
- HSPF2 = heat-pump heating efficiency. Higher is better.
- Installation and ductwork decide whether you actually get the efficiency you paid for.
Ratings help you shop, but they do not replace a professional sizing your system to your home. We have been doing exactly that across Northwest Indiana since 1963. If you want a straight recommendation, right-sized for your house and your budget, request a free estimate or call (219) 322-4649. We will translate the numbers into what they actually mean for your bill.
