Furnace Efficiency Ratings Explained: What Savannah Homeowners Should Know

Every furnace has an efficiency rating stamped on a yellow EnergyGuide label, but most homeowners have no idea what that number means or how it affects their heating costs. If you’re shopping for a new furnace in Savannah or wondering whether your current system is costing you more than it should, understanding efficiency ratings helps you make a smarter decision.

“Homeowners come in asking for the highest efficiency furnace available, and sometimes that’s the right choice,” says Bryan Donaldson, owner of On Time Air with over 25 years of HVAC experience. “But in Savannah, where we only run the furnace three or four months a year, the math on a 95% versus 80% unit is different than it is in Chicago or Boston.”

Here’s what the numbers mean and how they apply to heating a home in coastal Georgia.

What AFUE Means and Why It Matters

AFUE stands for Annual Fuel Utilization Efficiency. It measures the percentage of fuel a furnace converts into heat versus how much escapes as exhaust. A furnace rated at 80% AFUE turns 80 cents of every dollar you spend on gas into heat for your home. The other 20 cents goes up the flue as waste.

Current efficiency tiers for gas furnaces:

• 80% AFUE (standard efficiency): Meets the federal minimum for non-weatherized gas furnaces. These units use a conventional metal flue and are less expensive to purchase and install.
• 90-95% AFUE (high efficiency): These condensing furnaces extract additional heat from exhaust gases by cooling them until water vapor condenses. They use PVC venting instead of metal flues.
• 95-98% AFUE (ultra-high efficiency): Top-of-the-line models that capture nearly all available heat from combustion. Variable-speed blowers and modulating gas valves provide the most consistent temperatures and quietest operation.

Electric furnaces technically operate at 100% AFUE since they convert all electricity into heat. But electricity costs more per BTU than natural gas in most markets, including Georgia, so a 100% efficient electric furnace often costs more to run than an 80% gas unit.

How Efficiency Affects Your Heating Costs

The real question isn’t which furnace has the highest rating. It’s which one saves you the most money over its lifespan given your climate, gas prices, and how much you run the heat.

A practical comparison for Savannah:

Say your current furnace is a 20-year-old unit running at roughly 65% AFUE (typical for furnaces installed before 2000). You spend $800 per heating season on gas. Here’s what upgrading would save:

Upgrade To	Annual Gas Cost	Annual Savings	15-Year Savings
80% AFUE	~$650	~$150	~$2,250
95% AFUE	~$547	~$253	~$3,795

The 95% unit saves about $100 more per year than the 80% unit. But it also costs $1,000-$2,000 more upfront to purchase and install (condensing furnaces require PVC venting, a condensate drain, and sometimes electrical upgrades).

In Savannah, where the heating season runs roughly December through February with occasional use in March and November, the payback period on the efficiency premium is longer than in cities with six-month winters. For many Savannah homeowners, an 80% AFUE furnace delivers the best value. If you plan to stay in your home for 10+ years, the 95% model starts to make financial sense.

Old Furnace vs. New: What’s Changed

If your furnace was installed before 2010, it’s worth understanding how far the technology has come.

Furnaces from the 1990s and earlier:

• Typically 60-70% AFUE (30-40% of your gas bill was literally going out the chimney)
• Single-stage burners that run at full blast or not at all
• Single-speed blower motors that consume more electricity
• Standing pilot lights that burn gas 24/7 even when the furnace isn’t heating
• Basic thermostats with manual setback

Modern furnaces (2015+):

• 80-98% AFUE (far less wasted fuel)
• Modulating burners that adjust flame output to match heating demand
• Variable-speed ECM blower motors that use 75% less electricity than standard PSC motors
• Electronic ignition (no standing pilot light)
• Compatible with smart thermostats and zoning systems

The efficiency gains go beyond the AFUE rating. A variable-speed blower motor alone can save $100-$200 per year in electricity costs compared to a single-speed motor, and it runs quieter and distributes heat more evenly.

When Upgrading Makes Sense (and When It Doesn’t)

Not every furnace needs to be replaced with the highest-efficiency model available. Here’s how to think about the decision:

Upgrade to a new furnace if:

• Your current unit is 15-20+ years old
• You’re spending more than $300 per year on furnace repairs
• The heat exchanger is cracked (this is a safety issue, not just an efficiency issue)
• Your furnace runs constantly without maintaining the set temperature
• You hear loud banging, popping, or rattling when the furnace cycles

An 80% AFUE furnace makes sense if:

• You’re in Savannah with a short heating season
• Budget is a primary consideration
• You plan to sell the home within 5-7 years
• Your existing venting is standard metal flue (avoiding the cost of PVC conversion)

A 95%+ AFUE furnace makes sense if:

• You plan to stay in the home long-term (10+ years)
• Your home already has PVC venting from a previous high-efficiency unit
• You value the quieter, more consistent heating of variable-speed equipment
• You’re eligible for utility rebates or tax credits on high-efficiency equipment

On Time Air installs furnaces at every efficiency level from Goodman, Carrier, Trane, Lennox, and Rheem. We run a Manual J load calculation and discuss your priorities before recommending equipment, because the right furnace depends on your home and your budget, not on which model has the highest margin.

Energy Efficiency Beyond the Furnace

Your furnace efficiency rating only tells part of the story. The most efficient furnace in the world won’t save you money if the heat it produces leaks out through poor ductwork, insufficient insulation, or drafty windows.

Ductwork matters. Leaky ducts can waste 20-30% of heated air before it reaches your living spaces. If your ductwork runs through an unconditioned attic (common in Savannah homes), sealing and insulating those ducts can improve comfort and reduce heating costs as much as upgrading the furnace itself.

Thermostat programming saves fuel. Setting your thermostat back 7-10 degrees for 8 hours a day (while you’re at work or sleeping) can save up to 10% per year on heating costs, according to the Department of Energy. A programmable or smart thermostat handles this automatically.

Insulation and air sealing. Older Savannah homes, especially those in the historic district and Victorian-era neighborhoods, often have minimal wall insulation and significant air leakage around windows, doors, and foundations. Addressing these issues reduces the heating load on your furnace regardless of its efficiency rating.

Regular maintenance keeps efficiency high. A furnace that was 95% efficient when installed drops in performance without annual service. Dirty burners, clogged filters, and worn components all reduce output and increase fuel consumption.

Frequently Asked Questions

What is a good AFUE rating for a furnace?

In Savannah’s mild winter climate, an 80% AFUE furnace provides reliable, cost-effective heating for most homes. An 80% rating means the furnace converts 80% of the gas it burns into heat. For homeowners who want maximum efficiency and plan to stay long-term, 95%+ AFUE models capture nearly all available heat but cost more upfront.

How do I find my current furnace’s efficiency rating?

Check the yellow EnergyGuide label on the furnace cabinet. If the label is missing or unreadable, look for the model number on the data plate (usually inside the front panel) and search the manufacturer’s website. For furnaces older than 20 years, the rating may not be listed online. On Time Air can assess your current system’s efficiency during a maintenance visit.

Does a higher AFUE rating always mean lower bills?

Not necessarily. The savings depend on how much you run the furnace. In Savannah, where heating season is 3-4 months, the annual gas savings between an 80% and 95% furnace may only be $100-$150. If the high-efficiency unit costs $1,500 more, the payback period is 10-15 years. In a cold climate where the furnace runs 6-7 months, that same upgrade pays back in 4-5 years.

Are there rebates or tax credits for high-efficiency furnaces?

Federal tax credits are available for qualifying high-efficiency gas furnaces (97%+ AFUE) through the Energy Efficient Home Improvement Credit. Georgia Power and other local utilities occasionally offer rebates on high-efficiency heating equipment. Check the Database of State Incentives for Renewables & Efficiency (DSIRE) for current programs in your area.

Should I repair or replace my old furnace?

A common rule of thumb: if your furnace is 15+ years old and the repair costs more than $500, replacement usually makes more financial sense. Also consider the frequency of repairs. If you’ve called for service three or more times in the past two heating seasons, the cumulative repair costs signal a system that’s near end of life.

Talk to an HVAC Professional About Your Options

If you’re unsure whether to repair or replace your furnace, or you want to understand what efficiency level makes sense for your Savannah home, On Time Air can help. We serve homeowners across Savannah, Pooler, Richmond Hill, Rincon, and surrounding areas. As a veteran-owned business, we provide honest recommendations and written estimates that break down equipment, labor, and materials.

Call 912-210-4901 or request an estimate online to get started.