Why Gas Furnace Ratings are Important

If you are considering investing in a new furnace then you need to pay heed to the gas furnace ratings of the models that you are interested in. Gas furnaces that have higher ratings are more efficient, which means that they are better for the earth’s atmosphere and will save you on your energy bills.

When doing your research, look for gas furnace ratings of above 90% for the greatest savings on your energy bills. These furnaces may cost you more initially but they will pay for themselves within a couple of years in the savings on energy bills and you will be warm and comfy in the coldest of climes.

What to Look for when Choosing a Gas Furnace

One of the easiest ways to ensure that you are investing in the best, most efficient gas furnace is to look at what the efficiency rating of the furnace is. This is denoted by gas furnace ratings.

There are currently three types of energy ratings for furnaces; the Annual Fuel Utilization Efficiency (AFUE) rating, the Energy Guide label and the Energy Star rating.

The AFUE is a rating which is used to describe the efficiency of a furnace. It is shown as a percentage that is determined by calculating the ratio of heat produced compared to how much fuel is burned to produce that heat.

EnergyGuide Labels are black and yellow labels that are affixed to the outside of furnaces. The Energy Guide was developed by the Federal Trade Commission to inform the consumer of the range of energy used by furnaces of a similar size; the amount of energy that will be used by the furnace annually; and the estimated annual operating cost of the furnace, based on the current average energy cost.

ENERGY STAR Ratings – Products with the Energy Star logo, which is government-backed, denote products that offer the best performance, comfort and features whilst protecting the environment through the efficient use of energy, which reduces greenhouse gas emissions and other pollutants. Furnaces with the highest ratings are the most efficient, and only furnaces that have a rating of above 90% are awarded the Energy Star stamp of approval.

Although the above gas furnace ratings are important, they should be seen only as the guide they were intended to be, as there are many other factors which could possibly affect the efficiency of the furnace, so it is highly recommended that you speak to a professional regarding these matters in order to get professional advice which will allow you to make an informed decision as to which gas furnace to invest in.

What Are Gas Furnace Ratings?

According to federal regulations, all homes are required to have an AFUE rating of a minimum of 78%, but furnaces with this low rating are usually only found in manufactured homes. Only furnaces with an AFUE efficiency rating of above 90% meet the requirements set out by the Department of Energy’s ‘Energy Star’ program.

The gas furnace ratings categories are:

Low Efficiency Furnace: 55% to 72% AFUE

These gas furnace ratings are no longer legal for new furnaces. They are usually found on older furnaces which have non-electric standing pilot ignition, a single-stage furnace, a single speed blower, natural draft exhaust and a heavy cast-iron heat exchanger. These furnaces are often oil furnaces which have been converted to gas furnaces

Low Efficiency Furnace: 78% AFUE

This is the minimum AFUE allowed by federal law and furnaces with this low AFUE are generally used in space heating applications, manufactured homes and mobile homes. They generally have an electronic ignition, single-stage furnace and single-speed blower with a steel tube heat exchanger and a natural draft that creates a flow of combustion gases

Standard / Mid Efficiency Gas Furnace: 80% to 83% AFUE

Models with gas furnace ratings in this range have an electronic ignition, a single or two-stage furnace, single or variable blower, steel tube heat exchanger, and a natural draft that creates the flow of combustion gases.

High Efficiency Gas Furnace: 90% to 98% AFUE (Energy Star approved)

These models are Energy Star rated furnaces with 90% to 98% AFUE. These single, two-stage or modulating furnaces typically have a condensing furnace, electronic ignition, a variable speed blower, steel tube main heat exchanger and a secondary stainless steel heat exchanger for condensing flue gases. They also have a sealed combustion chamber.

Gas Furnace Ratings

How are Gas Furnace Ratings Established?

The metric that is used to measure the efficiency of a furnace is the Annual Fuel Utilization Efficiency, better known by its acronym AFUE. The AFUE measures ‘the amount of fuel which is converted to heat in the space in proportion to the amount of fuel which is put into the furnace.

The Energy Star program is a joint program of the U.S. Department of Energy and the U.S. Environmental Protection Agency, with a mandate to promote energy-saving appliances and devices. Items that qualify carry the Energy Star logo and utilize 20% to 30% less energy than prescribed by U.S. federal standards.

The Energy Star label is awarded to products that adhere to the strict requirements which are based on the following principles:

  • The product categories must contribute significantly to nationwide energy savings
  • Purchasers must be able to recover the difference in the price between the energy-efficient product and the less efficient product via savings on utility bills within a reasonable period of time.
  • Product performance and energy consumption must be able to be measured and verified via testing
  • To qualify, products must deliver performance and features as demanded by consumers, as well as increased energy efficiency
  • Energy efficiency can be achieved via widely available, non-proprietary technologies which are offered by more than one manufacturer
  • Labeling must differentiate products and be visible to purchasers.

What Impacts Gas Furnace Ratings?

Factors that impact on the efficiency of the gas furnace are varied and include:


Have a heat-loss analysis done before choosing a furnace for your home, as the size of the furnace will affect the gas furnace ratings and be important in how efficiently it works. This wastes energy, puts more wear and tear on its components, and creates temperature variations. Installing a furnace that is too big will be a waste of energy, as over sized furnaces cycle on and off too often. Installing one that is too small will not deliver the heat you need. An efficient furnace is the one that is sized right for the space in which it needs to operate.

Energy loss is measured in British Thermal Units (BTUs). A BTU is the rating which is given to the capacity of a furnace. One BTU is the amount of heat required to heat the temperature of one pound of water by 1 degree Fahrenheit. There are various online calculators which you can use to determine estimated BTU usage. In order to do this you need to know what the square footage, insulation and window data is.

An easier way of determining the correct size furnace for your home in order to get the gas furnace ratings that are advertised for a certain model is to get a furnace contractor on board to do the loss-analysis and the installation for you. A professional knows how to do this and about all the other factors that they need to take into consideration, such as the climate in your geographical area. Once they have done all the measurements and calculations they will be in a position to advise you on which furnace would be best suited to your particular home circumstances.


Condensing models offer greater efficiency because they capture and utilize heat that is lost in non-condensing models; heat that is captured even after the combustion exhaust gases have cooled and condensed. This is done by using two heat exchangers, a primary heat exchanger and a secondary heat exchanger which handles the corrosive condensed exhaust gases. These models all have an AFUE of 90% or higher.

Blower Motors:

Higher efficiency models have higher efficiency blower motors. Variable speed blowers impact the gas furnace ratings as they deliver warm air in different capacities to different areas of the home, which means that empty rooms or rooms that are rarely used are not being heated needlessly. Higher efficiency blower motors provide bigger savings.

Automatic Climate Control:

Automatic features such as automatic climate control allow your furnace to adjust itself to a pre-determined temperature automatically, and this saves on efficiency as you do not need to manually switch the furnace on and off all the time.

Duct Work:

Broken seals and cracked or broken duct work will also impact on the gas furnace ratings and negatively affect the efficiency of your furnace.

By following the right steps in researching what is available on the market, looking carefully at the area that you want to heat and employing the services of a professional, you are sure to get the right model furnace with the gas furnace ratings that will provide you and your family with the perfect indoor ambiance and temperature whilst saving you money on energy bills.