Understanding Furnace AFUE Ratings and How They Affect Heating Efficiency
Understanding Furnace AFUE Ratings and How They Affect Heating Efficiency
Guirguis Faltaos - 1/16/2024
When you need to replace your old furnace, energy efficiency is one of the most important things to consider. The efficiency of a furnace will directly impact how much you pay for heating. The Annual Fuel Utilization Efficiency (AFUE) rating measures the furnace’s efficiency. In this article, we’ll explain what you need to know about AFUE ratings and how to know what furnace is the best option.
AFUE Ratings Explained
In the US, furnace efficiency is measured using the AFUE rating scale. AFUE ratings are much easier to understand than AC efficiency ratings, as AFUE merely expresses how much energy the furnace effectively uses to heat the building and how much energy it wastes. The highest-efficiency furnace available is 98.5% AFUE, meaning that 98.5% of the energy it consumes goes directly towards heating the home.
Another way to think about AFUE ratings is in terms of how much money you spend on energy goes toward heating your home. If you have a 90% AFUE furnace, 90 cents out of every dollar you spend on natural gas, oil, or propane will be used for heating. The other 10 cents will be wasted. We’ll explain where the energy waste comes from in the next section. However, you only need to know that heating your home with a 90% AFUE will cost less than if you only had an 80% AFUE furnace.
Medium vs. High-Efficiency Furnaces
The US Department of Energy requires that all new gas furnaces sold in the country are at least 80% AFUE, and any new oil furnace must be at least 83% AFUE. All furnaces with a rating of 90% AFUE or greater are considered high-efficiency units, whereas anything under 90% AFUE is a medium-efficiency furnace.
Gas and oil furnaces are either traditional, non-condensing units or high-efficiency condensing units. Almost all non-condensing gas furnaces are rated at 80% AFUE, but you can find non-condensing oil furnaces that are slightly more efficient and have ratings at or above 85% AFUE. Any gas or oil furnace that is 90% AFUE or higher is a condensing furnace.
Why Condensing Furnaces Are More Energy Efficient
The difference between condensing and non-condensing furnaces is that condensing units have two heat exchangers, whereas non-condensing units have a single heat exchanger. The secondary heat exchanger in a condensing furnace enables it to achieve a higher energy-efficiency rating.
A heat exchanger can only absorb heat from the hot gases flowing through it at a specific rate. In a traditional, non-condensing furnace, the combustion gases retain quite a bit of latent heat when they exit the heat exchanger and flow through the exhaust flue pipe. This means lots of heat is lost, leading to greater energy waste.
In a condensing furnace, the combustion gases retain the same latent heat when they exit the primary heat exchanger. However, the gases then flow through the secondary heat exchanger, which absorbs anywhere from 10% to 18.5% of the remaining heat so that much less energy is wasted.
Why are they referred to as condensing furnaces? They absorb so much heat that the water vapor in the combustion gases condenses into liquid inside the secondary heat exchanger. This is why a condensing unit has a drain pan and drain pipes. This drainage system captures all of the condensation and drains the water away from the furnace.
Are High-Efficiency Furnaces Worth the Price?
As you probably suspect, the more efficient a furnace is, the more it will cost. Depending on the size of your house, you can usually expect to pay anywhere from a few hundred to possibly a few thousand dollars more for a high-efficiency condensing furnace than you would for a non-condensing furnace of the same size. Unless your home is quite small, installing a high-efficiency furnace in Fairfax, VA and the DC area will typically lower your heating costs by up to a few hundred dollars a year.
As such, the amount of money you save on heating costs will usually help a high-efficiency furnace essentially pay for itself in five to seven years at the most. When you factor the energy savings over the average 15-year lifespan of a new furnace, you can quickly start to see why high-efficiency furnaces are almost always the best option.
If you’re unsure what type of furnace you should install, you can count on our technicians for help. We specialize in furnace installation and can also service and repair your furnace to keep it heating effectively. For more information on our furnace services or if you need any AC, indoor air quality, or water heater services in Fairfax or the surrounding areas, call us at Eagles HVAC Services today.