High-Efficiency Gas Furnace vs. Regular Gas Furnace

Many homeowners are in the process of replacing their old traditional furnaces with new, high-efficiency models. Doing so significantly increases convenience and enhances overall comfort while reducing annual heating bills.

Above all, new furnace models are easier to integrate with intelligent home systems, a critical consideration as the digital revolution enters the home stretch.

This guide is designed to help you better understand furnace efficiency ratings to make an informed decision when the time comes.

Understanding Furnace Efficiency Ratings 

Let’s begin by understanding the origin of furnace efficiency ratings, what the numbers mean, and the regulations behind the numbers. The first thing you need to know is that whenever anyone mentions furnace efficiency ratings, they’re talking about Annual Fuel Utilization Efficiency (AFUE) ratings.

AFUE standards were established in 1987 by the US Department of Energy (DOE) and are national law under the National Energy Conservation Act. The efficiency ratings, which are displayed as percentages, range between 56% and 100%. The higher the AFUE value, the more efficient the furnace. The opposite is also true.

The DOE mandates that manufacturers clearly display the AFUE rating on the front faceplate of all furnaces.

What Do the Numbers Mean?

The annual fuel utilization efficiency (AFUE) value represents how much of the fuel used in your furnace converts into useful heat energy that goes towards keeping your home warm. It also tells you how much of the fuel goes to waste.

For example, an 85% AFUE gas furnace utilizes 85% of the gas to generate heating energy, while 15% goes to waste. Similarly, a 90% AFUE heater utilizes 90% of the fuel towards useful heating while 10% goes to waste.

Wasted fuel usually ends up as soot, smoke, and misdirected heat that eventually escapes the house via the chimney. Of course, it also escapes via water vapor and other combustion gases.

Overall, furnace AFUE efficiency ratings vary depending on;

  • Energy/fuel source
  • Size of the unit
  • Ignition style
  • Blower style
  • Type of heat exchanger
  • Whether it’s sealed or unsealed

Relevant Regulations 

The National Appliance Energy Conservation Act of 1987 set the AFUE standard to 78% through the beginning of 2015. However, the same law recently upped the standard to 80%. This means that all furnaces manufactured from 2015 onwards must be at least 80%.

Another critical regulation is that Energy Star-rated furnaces are typically more efficient. A furnace must be 90% AFUE or higher to become Energy Star Certified.

What is a High-Efficiency Gas Furnace?

Furnaces can be categorized as low-efficiency, mid-efficiency, or high-efficiency units depending on AFUE ratings. Generally, any furnace rated between 56% AFUE and 70% AFUE is considered a low-efficiency unit.

Most low-efficiency furnaces are single-stage units that start at full speed when it’s cold and go off completely once the temperatures warm up in spring.

Meanwhile, mid-efficiency furnaces range from 75% AFUE to 85% AFUE. Conventional gas furnaces in this range cost between $900 and $1,800. They are also characterized by electronic ignition systems and are often two-stage models that offer controlled heating.

Finally, high-efficiency heaters are units rated between 90% AFUE and 99.9% AFUE. These are typically sealed combustion furnaces with advanced heat exchangers that lose very little heat. They are also characterized by variable-speed blower systems.

Pros and Cons of High-Efficiency Gas Furnaces

High-efficiency furnaces come with many advantages and several downsides. Here’s what you need to know;


  • High efficiency: As the name suggests, high-efficiency furnaces are incredibly efficient. Some are 99% efficient or higher, meaning they only lose 1% of the fuel input.
  • Low heating bills: The incredible efficiency levels mean that high-efficiency furnaces guarantee low energy usage and thus low heating bills. Studies show that you can save up to 50% in heating bills by switching from a traditional gas furnace to a high-efficiency model.
  • Burn more cleanly: As we’ve mentioned, high-efficiency furnaces are typically sealed systems that vent all exhaust gases outside the house. Thus, there’s a reduced risk of carbon dioxide poisoning unless the system has blockages or leaks.
  • Tend to last longer: Studies show that modern high-efficiency furnaces last longer than standard efficiency models. Generally, you can expect to get about 5-10 more years from a high-efficiency heater.


  • High-upfront costs: Unfortunately, high-efficiency furnaces are very expensive. Although the actual cost varies from one unit to the next, most high-efficiency furnaces are priced above $10,000 and easily cost well over $15,000 with installation.  
  • New operational challenges: A few challenges unique to high-efficiency furnaces include blocked air inlet pipes, blocked exhaust vents, and drainage problems. These issues can cause frequent short cycling and heating outages.  

What is a Regular Gas Furnace?

The term regular furnace refers to low-efficiency and mid-efficiency furnaces. Generally, these are furnaces built before the DOE’s 2015 requirements came into effect.

High-Efficiency Gas Furnaces vs. Regular Gas Furnaces Side-by-Side 

Let’s now look at high-efficiency gas furnaces versus regular furnaces side-by-side for easier decision-making.


The first that comes to mind whenever a homeowner thinks about upgrading to a high-efficiency furnace is costs. Are high-efficiency models way more expensive than regular models, or do marketers exaggerate the prices? Unfortunately, the cost difference is significant. You may even pay twice the price of a regular furnace to acquire a high-efficiency model.

  • Regular furnace cost

A Regular furnace costs $700 to $3,500 or $2,100 on average for the unit alone. However, you’ll often spend $4,000 to $15,000 to purchase and install the unit. The prices vary depending on the size, efficiency, and technology involved. For instance, 40,000 BTU furnaces rated around 70% AFUE tend to cost around $800 to $1000. Meanwhile, a 120,000 BTU furnace at the same efficiency (70%) costs about $4,000. However, a 120,000 BTU unit rated 80% AFUE can cost up to $6,000.

  • High-efficiency furnace costs 

High-efficiency models are significantly more expensive. The cheapest high-efficiency furnaces are priced at around $3,000. These are typically small-size (around 40,000 BTU) furnaces from brands such as American Standard.

However, the larger units from luxury brands can cost as much as $15,000. For instance, a 120,000 BTU high-efficiency Lennox furnace costs around $15,000. Carrier and Bryant also have high-efficiency units costing over $13,000 before installation.


The next thing you may want to know is the efficiency differences. You’ve likely heard that high-efficiency furnaces are way more efficient than regular models. But, how much more efficient? More importantly, do the numbers make a tangible difference in the homeowner’s life?

  • Regular furnace efficiency 

As we’ve seen, regular furnaces are units rated between 56% and around 85% efficiency. This means that for every 100 liters of fuel you put into your furnace, 80% goes towards producing useful heat energy that helps keep you and your loved ones warm and toasty. However, 20% of the fuel is lost to the wind – sometimes literally.

We usually advise consumers to think of the losses in terms of money. Generally, an 80% efficient furnace means that you lose $20 for every $100 spent on natural gas. So, a 60% AFUE heater means only you only get $60 worth of heating for every $100 spent on gas. The result is usually higher energy bills as you also need to cover the losses.

  • High-efficiency furnace efficiency 

High-efficiency systems are significantly more efficient. As we saw earlier, only units rated 90% AFUE or higher qualify as high-efficiency systems. However, some high-efficiency furnaces are up to 99% efficient. It means that nearly every penny spent on gas translates to useful heat. As a result, high-efficiency furnaces can significantly cut your energy bill.

For instance, you instantly save a quarter (25%) of your energy bills when you upgrade from a 70% AFUE to a 95% AFUE unit.


Regular and high-efficiency furnaces also have different airflows because of different fans. This is another important consideration when shopping because the airflow determines how effectively the furnace distributes air throughout the room. Otherwise, you may be left with too many cold spots throughout the home.

  • Regular furnace airflow

Regular furnaces typically have either single-stage or two-stage blowers. Models on the lower end of the scale tend to have single-stage blowers that are either OFF or ON at 100% speed. Unfortunately, these blowers are highly inefficient and typically costly to run, resulting in high electricity bills.

However, many mid-efficiency units have dual-stage blowers that can be OFF at 0%, ON at 70%-80%, or ON at 100%. The low-speed setting (70% to 80%) allows you to keep the furnace running at a lower temperature to conserve energy.

  • High-efficiency furnace airflow

High-efficiency furnaces typically operate with variable speed blowers. A variable-speed blower doesn’t have fixed operational settings. Instead, it runs at any speed within a given range, typically 35% to 100%, depending on the heating requirements. Variable-speed blowers are extremely efficient, thus increasing energy savings.

Safety (moisture and venting)

Safety is a crucial concern for consumers seeking to upgrade from regular to high-efficiency furnaces. Perhaps you’ve heard stories about high-efficiency furnace risks and are now wondering whether an upgrade would be a good idea.

Unfortunately, the “rumors” have an element of truth. High-efficiency furnaces present significant safety challenges under certain circumstances. However, this doesn’t necessarily mean high-efficiency furnaces have a bigger safety risk than regular ones. Here’s what you need to know.

  • Regular furnace safety

Regular furnaces are generally safe. Although you must consciously take additional steps to prevent issues such as overheating and flame rollouts, these accidents often only happen if you don’t take good care of the appliance. Better still, the furnaces have safety switches to protect you if the appliance malfunctions.

  • High-efficiency furnace safety

The above issues are also present in high-efficiency furnaces. And, again, regular maintenance easily prevents accidents. Unfortunately, you’ll have to deal with two new issues – moisture and venting.

Excess moisture can cause dangerous short cycling. It can also cause internal damage. Meanwhile, poor venting or venting issues increase the risk of exhaust gas backdraft, which can cause gas poisoning and potential suffocation. So, you need to be extra careful. However, you don’t have to worry about the two as long as you ensure proper appliance maintenance.

Average lifetime 

Finally, regular and high-efficiency furnaces have different life spans because of the design variations and different efficiency levels.

  • Regular furnace lifespans

Regular furnaces typically last 15 to 30 years with good maintenance. On average, a regular furnace lasts 20 years. The short lifespan is mainly due to lower energy efficiency. These units produce more soot and other waste products that lead to faster corrosion, rusting, and general wear. The large volume of waste products also means increased maintenance needs.

  • High-efficiency furnace lifetime

High-efficiency furnaces tend to last slightly longer because of advanced build technology. Better still, high-efficiency furnaces produce very few waste products. So, the risk of internal parts corrosion and rusting is minimal.  

Generally, a high-efficiency furnace lasts 20-30 years, with an average 25-year lifespan. However, some units last up to 40 years.


  • Is a high-efficiency furnace worth the extra money? Yes, high-efficiency furnaces are worth the extra investment. in fact, the furnaces usually pay for themselves after about 8-10 years.
  • Are high-efficiency furnaces cheaper to run? Yes, high-efficiency furnaces are cheaper to run. It costs up to 45% less to run a high-efficiency heater.
  • 80 vs. 96 AFUE furnaces, which is better? 96% AFUE furnaces are better as they only lose 4% of fuel compared to 80% AFUE units that waste 20% of the fuel.
  • 95 vs. 98 AFUE furnace, which is better? 98% AFUE models are slightly more efficient than 96% AFUE units. However, the two units will be more or less the same design-wise.
  • 90 vs. 95 AFUE furnace, which is better? 90% AFUE is the official high-efficiency cutoff point. So, 90% AFUE furnaces are still very good. However, 95% AFUE units are Energy Star certified, highly-efficient systems.  
  • 80 vs. 90 AFUE furnace, which is better? Obviously, a 90% AFUE furnace is more efficient than an 80% AFUE unit. However, you’ll also note significant differences between the two. For instance, 80% AFUE furnaces are typically dual-stage heaters, while 90% AFUE units are variable-speed furnaces.
  • 92 vs. 96 AFUE furnaces, which is better? There isn’t a big difference between 92% AFUE and 96% AFUE furnaces. However, 96% AFUE units are slightly more efficient and will save you an extra $4 for every $100 spent on heating.


That’s all you need to make an informed decision when you finally decide to ditch the regular furnace for a high-efficiency unit. Just make sure you’re prepared financially. If you must save up for a few more months to find the perfect high-efficiency furnace, so be it.