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Gas Furnace Buyers Guide 2020

If you’re having a hard time finding the best gas furnace for your home, you’ve come to the right place. This 2020 residential furnace buyer’s guide is here to help you know what to look for in a furnace and how your specific preferences can be met. 

2020 Gas Furnace Buying Guide

You may also be interested in our 2020 Most Efficient Gas Furnaces guide, which lists the most energy efficient gas furnace manufacturers, such as Lennox, Ruud, Heil, Trane, and Carrier. 

Gas Furnace Efficiency Options

You will find the gas furnace efficiency options between 80% and 95%-or higher below. 

As you peruse our list, which goes from most to least efficient furnace options, note that Annualized Fuel Utilization Efficiency (AFUE) is like gas mileage for furnaces. It shows how much heat the furnace creates per gas consumed. In other words, a furnace listed as 95% AFUE makes use of 95% of the gas it burns, while only losing the remaining 5% with the combustion exhaust gases that go up the chimney.

95% or Higher Gas Furnace Efficiency 

Brands within this range include Lennox, with its SLP98V gas furnace model at 98.7% heat-efficient, and Trane, with its XC95M model at 97.3%. 

All the leading furnace brands manufacture gas furnaces in this range to provide you the most out of your furnace. These models achieve excellent heat efficiency with a variable-capacity gas valve (see more in the “Performance Options” section), secondary heat exchanger, and condensing technology that produces more heat from the moisture that comes as a byproduct of combustion.  

Of course, furnaces within this heat-efficiency range will be pricier upfront than the furnaces listed below. But keep in mind that the higher the heat efficiency, the more money you will save over time. 

Here is Energy Star's 2020 list of the Most Efficient Gas Furnaces.

ENERGY STAR Most Efficient in 2020

90%-95% Heat Efficiency 

While not as heat efficient as the gas furnaces above, furnaces in this range are still markedly useful, utilizing a secondary heat exchanger that transfers additional heat from the combustion gases before they are exhausted.

Most furnaces in this range and higher are Energy Star rated, which means the products meet a strict set of criteria established by the U.S. Department of Energy. Installing one of these furnaces may also qualify for credits and rebates from your energy company

Consumers who purchase 90%-95% efficient furnaces often give these reasons for why they’re satisfied with their product: 

  • Lower energy costs when compared to an 80% efficient furnace
  • Using their furnaces long-term, homeowners easily earned back the cost of their furnaces in heat bill savings
  • Those looking to sell their house after furnace installation found a 90%-95% furnace was a strong incentive for buyers
  • Eco-friendly and low energy use

80% Heat Efficiency 

As the saying goes, you get what you pay for. This certainly doesn’t mean gas furnaces with 80% heat efficiency are poor products—they can be quite good. But while the initial cost of furnaces is cheaper, they lose 20% of the heat they produce, which is far more than furnaces with 90% or higher efficiency.  

The primary reason for the lower efficiency level is because these furnaces have a single heat exchanger. 

However, there are some good reasons to consider purchasing this type of furnace:

  • If your winters are mild-to-warm, your heat bills are naturally lower. So, spending $1,000 more for a higher efficiency furnace only to save $5-$10 a bill simply isn’t cost effective for you. 
  • If you’re selling your home soon, you won’t earn your money back in heat efficiency with a pricier furnace. (This said, you may find an 80% efficiency furnace will deter some buyers. You’ll have to decide if the upfront furnace price or the buyer’s preference is more priority for you.)
  • It’ll be more cost-effective for you if the furnace will only be used part-time, such as in a vacation home. 

Efficiency and Climate

These standards never went into effect. However, they do show a good minimum-efficiency bar for each region of the country. AC and furnace efficiencies are listed.

Performance Options 

What are your preferences for your furnace as it comes to heat balance, humidity, and noise? Below are three furnace performance options to choose from. Keep in mind that each choice affects the efficiency in some way.

Single-Stage Furnaces: These run at 100% capacity to heat your home in the harshest weather. 


  • Inexpensive compared to furnaces of the same efficiency and better performance
  • Most single-stage furnaces are 80% efficiency models. However, the technology has become more advanced/efficient over the years, and single-stage models are available in the mid-90s for efficiency.
  • Can come Energy Star rated


  • 100% capacity furnaces are loud, since they run “full blast” all the time
  • By the time the thermostat reaches set temperature, full-capacity furnaces can warm your home a degree or two more than preferred 

Two-Stage Furnaces: These furnaces burn at 65% capacity most of the time, only working on higher capacity when outside temperatures dramatically drop, or when you raise your thermostat setting. 


  • Still noisy, but quieter
  • Better heat balance
  • Less wasted heat/more efficient 
  • Better humidity control  


  • Higher upfront cost than single-stage furnaces

Variable-Capacity Furnaces: These run at varying capacities and speeds, as they monitor the temperature of your home and adjust accordingly. To produce the precise amount of heat for your home, they modulate in increments of 1% or less.


  • Most heat efficient compared to single- or two-stage furnaces
  • Best temperature balance
  • Best humidity control when equipped with a humidifier


  •  Costs 25%-35% more than two-stage furnaces

Gas Furnace Capacity

Industries use the British thermal unit (BTU) as a standard measurement for heat efficiency per hour of use. Furnaces begin around 40,000 BTU/hour and can be as high as 155,000 BTU/hour. 

It is imperative that you find the right size furnace for your home. If you’re unsure what size you need, contact your nearest or most reliable HVAC company to test and determine it for you.

The testing process is called a “Manual J. load calculation.” To determine the proper furnace size, this calculation anticipates:

  • The climate around your house
  • Aspects of your home’s construction
  • Foundation type
  • Roofing materials 
  • Level of insulation in walls and the ceiling 
  • Number of windows and window types 
  • Doors

If you’ve updated any of these factors recently, such as installing new windows or adding another layer of insulation in your attic, then your new furnace should be smaller than the furnace being replaced.  

Something to note is that furnaces have heat input (BTUs created) and heat output (BTU efficiency ratings). The output is what truly matters, as it reveals how much heat is used up or wasted. 

So, if your home needs a furnace with 100,000 BTU capacity, for example, that is the amount of heat that flows through your home, but not the total heat created. Refer to the equations below as reference for calculating output:

  • 130,000 BTU input x 80% efficiency = 104,000 BTU output
  • 110,000 BTU input x 90% = 99,000 BTU output
  • 105,000 BTU input x 95% = 99,750 BTU output
  • 105,000 BTU input x 97% = 101,850 BTU output
  • 100,000 BTU input x 98% = 98,000 BTU output

Buying Tips 

Here are some basic tips to keep in mind as you look for the right gas furnace:

  • Is climate control important to you? If so,
    • An 80% heat-efficient furnace will work best if you live in a warmer climate. 
    • A 90%-95% heat-efficient furnace works best in a cooler climate.
    • A variable-capacity furnace works best in a harsher climate.
  • The colder your winters are, your best bet is purchasing a higher heat-efficient furnace.
  • The longer you plan on living in your home, the more you’ll save with a heat-efficient furnace. 
  • Is indoor comfort control a high priority for you? If not, then you will save more money purchasing a single-stage furnace at the best-fitted efficiency level for your climate. 
  • Is being eco-friendly important to you? If yes, then doing these will reduce the amount of energy your furnace wastes:
    • Purchasing the most efficient furnace you can afford for cool or cold climates.
    •  Choosing a heat pump instead for hot or cool climates.
    •  Using a dual fuel system with a heat pump and a furnace for cold-to-harsh climates. A dual fuel system uses a heat pump for heating in above-freezing temperatures and a gas furnace for below-freezing. 

Certified and Professional Furnace Installation 

Installing a furnace is not only too difficult for a DIY project, but we understand that even HVAC professionals can be liable for poor installation at times. It pays, then, to hire a qualified contractor who is both certified and experienced with furnace installation. 

Make sure to get estimates from multiple HVAC companies to learn about the quality of work they provide and which of the bunch has the best price. 

Another option is to use our Free Estimates tab for several written estimates from some of the top HVAC technicians in your area. Each company is prescreened for experience and to ensure it is licensed and insured. The companies also recognize that they are competing with each other, which means they will be less likely to take shortcuts in the installation process or to over price you.

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