High-efficiency gas furnaces versus regular gas heaters: just what is the difference? Trust the Chicago HVAC team at Aircor—it all comes down to a furnace’s AFUE rating (Annual Fuel Utilization Efficiency). A standard or low-efficiency gas furnace has an AFUE rating of between 80%–85%. In a high-efficiency furnace, the AFUE rating, according to the model ranges between 90%–95%.

But AFUE ratings don’t paint the whole picture. Because if you buy an 80%-efficiency furnace that doesn’t mean you won’t get a well-engineered and reliable furnace. You will. And it can give good service for 10 to 20 years. Modern technology has made it possible for low-efficiency furnaces to conserve energy better than the outdated gravity furnaces of the past.

To talk about today’s high-efficiency gas furnaces you need to know they have changed greatly over the past 10 years. High-efficiency gas heaters can support AFUE ratings as high as 95%. And these programmable models come with many extra features to help conserve energy output.

To explain further the differences between a low-efficiency gas furnace versus a high-efficiency gas furnace let’s consider four components of both.

  1. Condensing Process. Furnace vent condensation concerns come with regular gas furnaces. These gas furnaces (with an AFUE rating of 80%) exhaust 20% of its heating energy up the furnace’s vent.

High-efficiency furnaces rated at 90% AFUE or better are known as condensing furnaces. A condensing furnace possesses an integrated extra heat exchanger, whose job is to replenish the 20% lost in a low-efficiency heater. This is accomplished when combustion gases are redirected, condensed, and converted to water, releasing heat, and the heat removed by the extra heat exchanger. The result is the AFUE percentage bumps up, reducing the cost of operation.

  1. Adaptable-Speed ECM Blower. 80%-efficiency furnaces possess common one-speed, on-and-off blowers. When turned on the blowers run at 100% of capacity and eat approximately 500 watts of electrical power. Because of the frequent on-and-off cycles, temperatures fluctuate conspicuously from room to room. The drawback of a one-speed blower is once a home is completely heated, a blower operating at full capacity is not necessary to maintain the comfort level of a home. In other words, electricity is being wasted.

In contrast, the adaptable ECM (electrical commutated motors) blowers on 90%-efficiency heaters operate almost all of the time, stopping the on-and-off cycling, which produces temperature fluctuations. Because they run at a lower heat volume, they only use approximately 80 watts, a considerable savings in energy.

  1. Multi-Stage Burners. With an 80%-efficiency furnace the burners operate at 100% of capacity. In temperate weather conditions, this high-capacity burner is only useful for the cold season, otherwise it uses up energy needlessly.

A 90%-efficiency furnace contains multi-stage burners that intuit what temperatures are necessary to maintain the comfort level of a home. As heating requirements lessen, the multi-stage burner automatically switches to a lower, energy-savings level. The benefits include reduced power bills, energy conservation, and cleaner emissions.

  1. Sealed Combustion. A low-efficiency furnace uses the air from inside the home to initiate the burner flame. As a consequence, this lowers the humidity in living spaces and increases winter-air symptoms of itchy skin, irritated throat, and static electricity.

A more serious issue is the possibility of carbon monoxide being released into the home due to backdrafts. This means combustion gases don’t go up the exhaust vent like they should, but are diverted into living spaces.

A high-efficiency furnace contains a sealed-off combustion unit that protects the home from fumes. Two pipes work in conjunction to one, route the combusted air outside the home, and two, exhaust the gases. As a result, the home’s humidity level is protected.