How long does a furnace last?

What the federal estimate and a manufacturer say

A December 2023 DOE final rule on efficiency standards covers two kinds of gas furnace: non-weatherized gas furnaces and mobile home gas furnaces. The rule says, "DOE estimates the average product lifetime to be 21.5 years" for both. That is an average, so some furnaces last fewer years and some last more.

To reach that figure, DOE used appliance age data from surveys, along with historical furnace shipments. The rule says, "The survival function provides a lifetime range from minimum to maximum, as well as an average lifetime."

Carrier, a furnace manufacturer, says a well-maintained furnace typically lasts 15 to 20 years. It adds that a high-quality furnace can potentially last up to 30 years with proper installation, regular maintenance and appropriate use. Carrier calls these ranges general guidelines.

ENERGY STAR lists a furnace more than 15 years old as one sign to consider replacing it. Our reading: treat 15 years as the age to start planning.

Heating hours in the DOE rule, and Florida heating use

The DOE rule uses two regional averages: 22.5 years in the North and 20.2 years in the rest of the country. It says the split is based only on the difference in operating hours. DOE assumed that equipment operated for fewer hours will have a longer service lifetime.

The rule also says northern furnaces are generally higher capacity, to meet the higher heating load, so they can have lower operating hours.

A U.S. Energy Information Administration (EIA) brief from its 2009 household energy survey says Florida residents use space heating equipment much less than those in other states. It adds that most Florida households still use some heating in winter. Most of those use electric furnaces or heat pumps. For heat pumps, see when to replace a heat pump. For electric furnaces, see gas furnace vs electric strip heat.

The rule adds that furnace replacements in the rest of the country are more likely to be linked to a paired central air conditioner. For air conditioners, see how long AC units last in Florida.

This page does not give a Florida-specific furnace lifespan.

Does an old furnace lose efficiency?

One federal study found little loss. AFUE stands for annual fuel utilization efficiency, the DOE's efficiency rating for a gas furnace, measured in a lab. A 2015 report from the DOE's Building America program looked at whether that rating still holds after years of use.

The researchers removed nine gas furnaces, with 15 to 24 years of field service, from homes in Iowa. They tested them in a lab and compared the results with each furnace's original rating. The report says the values were similar, "implying that equipment performance did not significantly decrease over 15–24 years of operation."

The report adds a condition. Rated AFUE is a good guide over a furnace's useful life if it is installed according to the maker's instructions. It calls correct installation "a key driver in this finding." The same report notes that gas furnaces can operate with little maintenance over a 30-year period or longer.

Our reading: nine furnaces in Iowa are a small sample, and most Florida homes that heat use electric furnaces or heat pumps. Furnace types and efficiency explains the ratings in more detail.

What shortens a furnace's life

Carrier names four key variables: size, installation quality, maintenance habits and usage patterns. It says systems that are too large will turn on and off rapidly. It also says poorly designed or sealed ducts restrict airflow, forcing the system to work harder.

Maintenance shows up in both sources. ENERGY STAR says a dirty filter can damage your equipment, "leading to early failure." It advises inspecting, cleaning or changing the air filter once a month. It also says faulty electrical connections can reduce the life of major components.

ENERGY STAR recommends a yearly pre-season check-up by a contractor, with the heating system checked in the fall. ENERGY STAR's maintenance checklist for heating includes checking gas (or oil) connections, gas pressure, burner combustion and the heat exchanger. What a heating tune-up covers walks through that visit.

Signs a furnace is nearing the end

Carrier says, "Even with the best care, every mechanical system eventually reaches the end of its usefulness." Its list of signs includes frequent service calls and breakdowns, and uneven temperatures through the home. It also lists a system that struggles to hold the thermostat setting, a furnace blowing cold air, and new or unusual noises.

ENERGY STAR's list overlaps. It names frequent repairs while energy bills go up, rooms that are too hot or too cold, humidity problems, excessive dust and a noisy system. ENERGY STAR says leaky ducts can pull particles and air from attics and crawl spaces and spread them through the house.

ENERGY STAR says a dirty burner or cracked heat exchanger can make the equipment operate less safely. A cracked heat exchanger is covered in furnace heat exchanger cracks.

Our reading: age by itself is a reason to get an inspection, not proof that the furnace must go. Ask for a written finding on what is wrong and what it would take to fix.