When choosing a residential gas furnace, efficiency isn’t just a technical detail — it directly affects comfort, energy costs, and long-term performance. One of the most important measurements to understand is AFUE, or Annual Fuel Utilization Efficiency. This rating tells you how effectively a furnace converts fuel into usable heat.

Below, Rick Kincel breaks down what AFUE means, how to interpret it, and why upcoming federal changes will impact future installations.

What Is AFUE?

AFUE stands for Annual Fuel Utilization Efficiency, and it’s expressed as a percentage. This percentage represents how much of the fuel you pay for actually becomes heat in your home — and how much is wasted through the venting process.

For example:

• A 70% AFUE furnace sends 70% of the heat into your home, while 30% escapes out the vent.
• An 80% AFUE furnace sends 80% into your home and wastes 20%.
• A 90% AFUE furnace delivers 90% heat into the home and loses only 10%.

The higher the AFUE, the more efficiently the system performs and the lower the heating costs over time.

How Furnace AFUE Ratings Have Evolved

Over the years, furnace efficiency has steadily increased. Rick outlines three main efficiency categories:

Older Furnaces (60%–70% AFUE)

These often used pilot lights and lost a significant amount of heat up the flue.

Mid-Efficiency Furnaces (72%–80% AFUE)

Common throughout the Southern U.S. for the last two decades, these remain standard in many homes today.

High-Efficiency Furnaces (90%–98% AFUE)

More common in colder climates, these Energy Star–rated units maximize heat output by reducing waste through advanced venting and secondary heat exchangers.

AFUE and Real-World Heating Costs

Rick shares an easy way to visualize efficiency:

If you spend $100 on fuel, your furnace determines how much of that money actually warms your house.

• With a 70% AFUE unit, $30 is wasted.
• With an 80% AFUE unit, $20 is wasted.
• With a 90% AFUE unit, only $10 is wasted.

Higher AFUE means lower operating costs — but it also usually means a higher upfront equipment and installation cost.

Understanding Furnace Types

Rick also explains how furnace airflow design affects installation options:

• Upflow: Installed in closets; return at bottom, supply at top.
• Downflow: Common in mobile homes; return at top, supply from the floor.
• Horizontal: Installed in attics; return on one end, supply on the other.

Knowing these configurations helps determine which efficiency options are possible in your space.

New DOE Standards Coming in 2029

A major change is on the horizon. The Department of Energy (DOE) has raised the minimum allowable furnace efficiency to 95% AFUE starting in 2029.

This means:

• 80% furnaces — currently the minimum — will no longer meet federal requirements.
• High-efficiency models will become the new standard.

Homeowners planning long-term upgrades may benefit from choosing a 80%+ AFUE unit now to stay ahead of regulations.

The Bottom Line

AFUE is more than a number — it’s a direct indicator of how well your furnace turns energy into comfort.

• Higher AFUE = lower energy waste and better long-term savings.
• Lower AFUE = more heat (and money) lost through the vent system.

As efficiency standards continue to rise, homeowners and contractors can prepare by understanding which systems offer the best balance of performance, cost, and regulatory readiness.

Airflow has always been one of my passions, and with today’s newer equipment, the old “this is how we’ve always done it” approach just doesn’t cut it anymore.

Modern furnaces and coils demand more precision. Heaters now push air through tube heat exchangers in a very turbulent pattern, while coils often use an N-style design that requires proper airflow through each slab to perform efficiently. Put these two together — even when the equipment is the same physical size — and you can end up with an unreliable airflow pattern that impacts comfort and performance.

The Solution: Transitions

One of the best tools for smoothing out airflow is a transition installed between the furnace and the coil — specifically, the SST2 transition.

If you’ve heard of it before and dismissed it, it’s time to reconsider. Adding this transition dramatically improves system performance, prevents installation issues, and makes service easier down the road.

The choice is simple:

• Install the transition upfront at a small cost.
• Or, skip it — and risk multiple callbacks, frustrated customers, and free return visits.

Which would you rather do?

Contractor Experiences

Don’t just take my word for it. Here’s what a few of our contractors had to say after learning the importance of transitions the hard way:

John Neal, Southern A/C Solutions LLC, Jackson, MS   
“Once you eat a job due to airflow restrictions from a coil and furnace that are different dimensions, you will not chew that hard again. I AM EDUCATED NOW.”   
We agree, John — the School of Hard Knocks has a lousy lunchroom.

Jordan Schexnider, Chapman’s A/C and Heating, Scott, LA   
“These transitions improve equipment performance and help my maintenance guys service the unit easier. That’s a win / win!”   
Absolutely, Jordan — better airflow and easier service calls are a win for everyone.

Devin Baldridge, A+ Comfort Consulting, Chalmette, LA   
“After about 6 hrs of troubleshooting I called Tech Support, and they informed me of a transition from my coil to furnace for better flow. We’ve installed RUUD furnaces for years, without any hiccups. I didn’t believe it until I installed the transition. The Static pressure was .98 before adding the transition, and .58 after. I will 100% be installing these transitions, call me crazy, but with a .4 in drop in static pressure on this system, it speaks volumes. I have learned a valuable lesson.”   
Thanks, Devin. That kind of real-world improvement speaks louder than any sales pitch.

Why It Matters

The HVAC industry is evolving, and transitions are part of that evolution. Think about it:

• Less wasted time – no 6-hour troubleshooting calls.
• Faster maintenance – easier access for techs.
• Fewer callbacks – which means lower costs and happier customers.

It’s not a waste of time. It’s not a waste of money. It’s a smart investment in your business.

Ready to Make the Change?

Talk to your local Coburn’s branch and ask about SST2 transitions for your next install. Make them a standard part of your jobs — and save yourself the frustration of learning airflow lessons the hard way.