Gas Furnace Features: A Comparison Guide

Gas Furnace Features


If you are like most homeowners, you don’t pay attention to your gas furnace until you start feeling an uncomfortable chill in your home. However, if you are considering replacing your gas furnace, you may want to get familiar with the latest options and features available.  The good news is that today’s energy-efficient gas furnaces aren’t the same as your parent’s gas furnaces!


Bigger Isn’t Better


Size: The size of your gas furnace (which is measured in BTUs or ‘British Thermal Units’), is not a feature. Bigger is not always better, and it is important to clarify this! A gas furnace that is too large or too small may not provide the consistent warmth you expect from your heating system. A gas furnace should be sized “just right” for your specific home. Your old gas furnace may look larger than the new energy-efficient model that you are going to purchase.  Many of today’s gas furnaces are not only more energy-efficient than in years’ past, but they can also reach higher efficiencies in a much smaller sized unit. 

Your installation technician should confirm the size or BTUs required by performing a Manual J load calculation.  This calculation evaluates the heating needs of your entire home by assessing square footage, number and location of windows, insulation values, and more. When it comes to gas furnaces, the only size that matters is the right size that provides indoor comfort on those cold winter nights!


Setting the Stage for Comfort


Stage:  A gas furnace’s stage may be referred to as single-stage, two-stage, or multi-stage (modulating). The stage is all about the gas valve and the burner. The different stages work similar to how the heat is adjusted on your gas grill, gas oven or gas stovetop. 

  • Single-Stage Gas Furnace:  When the gas burner is ignited, the fuel enters at one constant flow. It is either ON or OFF and doesn’t offer the option of adjusting the gas flow.
  • Two-Stage Gas Furnace:  A two-stage gas furnace has a high and low setting on the gas burner. This feature allows for two levels of operation depending on your heating needs — full gas flow for when the demand for more heat is needed or a lower flow for milder days. A two-stage gas furnace may increase efficiency and a supply a more consistent indoor temperature when compared to a single stage unit. Typically a two-stage gas furnace is designed to operate at the low speed as much as possible.
  • Multi-stage or Modulating Gas Furnace: Like the heat on your gas appliances, a stove or grill, the burner electronically adjusts based on your thermostat or control system settings to provide the right amount of heat required to maintain the temperature on your thermostat or control system. This feature allows for precise heating control and energy-efficiency when compared to a single stage unit. Similar to a two-stage system, this type of gas furnace is designed to operate on the lowest speed to provide energy-efficient heating.


Heated Air in Motion


Gas Furnace Blower Motor: Just like the name suggests, the blower motor controls the amount of heated air pushed through the air ducts to the spaces of your home.  Below are three blower motor options, each with an increasing level of comfort control.

  • Single-Speed:  A single-speed option has two positions, ON or OFF. When on, the blower is designed to push a specific volume of air through the ductwork. When your thermostat or control system reaches the desired set temperature, the single-speed blower turns off. 
  • Multi-Speed: The multi-speed blower is similar to the temperature control fan installed in your car. This type of blower offers a series of set operating speeds, from a low rate of air being pushed into the ductwork to a higher rate. This alleviates the “cold air blow’ often associated with single-speed furnaces.
  • Variable-Speed: A variable speed blower motor operates at various speeds to precisely control the amount of airflow throughout your home. According to the Office of Energy Efficiency & Renewable Energy, a variable-speed motor running continuously at a half speed may use up to 75% less power than that a single-stage motor uses to move the same amount of air.1




AFUE (Annual Fuel Utilization Efficiency): The AFUE rates how effective your gas furnace is at converting gas to heat used to warm your home. This efficiency rating may range between 80% and 98% AFUE.  The higher the percentage number, the higher the certified energy-efficiency level. 

80% AFUE (non-condensing gas furnace)

  • Minimum U.S. national efficiency rating.
  • Equipment may cost less for initial installation, but the 80% AFUE gas furnace many have higher operational cost than higher AFUE furnaces.
  • Vents exhaust gases out of the home through chimney liner or metal flue pipe, typically through the roof.

90%-98% AFUE (condensing gas furnace)

  • Utilizes a second heat exchanger to heat the air from condensed exhaust gases which helps increase the energy efficiency rating.
  • May have higher upfront equipment and installation costs than a lower AFUE model.
  • Certain high-efficiency furnaces may qualify for tax credits. (Ask your local professional HVAC dealer about tax credits that may apply to your location)
  • Often come with additional energy-efficient features designed to improve your overall indoor comfort.
  • During installation, a 90+% AFUE may require retrofitted venting if your system is upgrading from a less efficient gas furnace.


Some Like it Hot


The heat exchanger is an essential component of a gas furnace’s performance.  Combustion from burning fossil fuels creates extreme heat inside the heat exchanger.  Your indoor air is circulated through the heat exchanger, warming it to be re-circulated back to your conditioned indoor living areas.

Heat exchanger features may include: 

  • One-piece, tubular construction: Joints are eliminated, reducing weak areas. 
  • Wrinkle bend technology: This maintains the wall thickness of a curved section is of a heat exchanger. Additionally, the wrinkle-bend technology provides a “turbulation” effect for excellent heat transfer properties.
  • Sloped design: The sloped angle of the secondary heat exchanger allows for optimal condensate drainage which helps improve the performance of the heat exchanger.
  • Stainless steel or aluminized steel: Heat exchanger materials with unique thermal and corrosion properties are selected to provide reliable warmth in your home for many years. A gas furnace’s heat exchanger is designed specifically to optimize performance. If you have questions about the specifics of heat exchangers, ask you licensed professional HVAC dealer.




Select gas furnaces have made significant technological advancements over the past few years. Your new gas furnace is rather smart! Some innovative features may include:

  • A diagnostic control board that may be capable of communicating system performance. This feature may simplify installation, maintenance, and repair of your gas furnace.
  • Internet connectivity that allows for remote control programming and system management from any location.
  • Automated maintenance reminders on the thermostat control system. These may include filter changes, scheduled maintenance reminders, and other indoor air quality-related products.




A gas furnace is an investment in your home and your family’s comfort. It helps to know that your equipment is backed by a manufacturer’s limited warranty. An important feature for any investment is the peace-of-mind that comes with a limited warranty, so ask your licensed professional HVAC dealer about the limited warranty on the furnace, as well as about purchasing an extended service contract on the furnace.   

For specific limited warranty information related to your new gas furnace, be sure to read your gas furnace model’s limited warranty certificate!

The Importance of Installation


The performance and reliability of a new gas furnace may be directly linked to a professional installation.  Your local HVAC dealer should have a reputation for quality, value, and customer service. An improperly installed gas furnace can lead to performance issues that may shorten the life of your system and cost you in the long run. A National Institute of Standards and Technology (NIST) study states that if your high-efficiency equipment is installed improperly, it may not be running as efficiently as you think!2 

To ensure you hire a qualified professional that best fits the job, be sure to: 

  • Check the manufacturer’s independent dealer locator
  • Search the internet
  • Get referrals
  • Read reviews

Whether your home’s heating system is in need of routine maintenance, emergency repairs or a total replacement, selecting a qualified HVAC contractor is essential.



1 Office of Energy Efficiency & Renewable Energy. Variable-speed, low-cost motor for residential HVAC systems. n.d. 1 May 2017. <>.
2 Office of Energy Efficiency & Renewable Energy. Variable-speed, low-cost motor for residential HVAC systems. n.d. 1 May 2017. <>.