During those last blustery days of autumn, you’ll often pass by your neighbor’s house and notice their technician paying them a visit-and for good reason. Aside from the discomfort of chilling in your living room while waiting on an emergency repair, a broken furnace can release contaminants into your house that can make your family sick.

So how do you know if it’s time to invest in a new heating system? Here is a checklist of telltale signs that your furnace is on its way out so you can plan for your next one in advance- rather than in a panic.

Your furnace is very old

According to ENERGY STAR, a program run by the U.S. Environmental Protection Agency (EPA) and U.S. Department of Energy (DOE), you should replace a furnace that’s over 15 years old. As part of its sustainability mission, the program encourages consumers to purchase an ENERGY STAR rated furnace, which is considered 15% more energy efficient than other furnaces on the market.

These ENERGY STAR® certified furnaces are manufactured to prevent greenhouse gas emissions by meeting rigorous energy efficiency performance levels set by the EPA. Thus, investing in this type of furnace may qualify you for federal energy tax credits and local utility rebates.

How do you define efficiency for furnaces? Check their Annual Fuel Utilization Efficiency (AFUE) rating. The AFUE system measures how much fuel is used by a furnace, which is essentially how well a unit converts fuel to heat inside your home. The minimum AFUE rating requirement for furnaces on the market today is 80%, but several systems come with much higher ratings. As a rule of thumb, the higher the AFUE percentage is the more efficient the furnace or heat pump is.

Your furnace’s fuel type is directly tied to its efficiency, which is why oil and gas furnaces have lower AFUE ratings than electric ones. Furnaces with AFUE ratings between 90% – 98% are considered “high efficiency” furnaces. These units can cost more upfront but can save money and energy over time in lower energy bills.

What’s another way to tell if your system is aged? Look for the pilot light, or lack thereof. Since 2010 gas furnaces have generally been developed without a pilot light that continuously burns. Instead, newer systems use electronic ignition systems that light only as needed. In short, if your furnace has a pilot light, then it could be decades old, or at least past its prime.

An unexplained spike in your heating bill

We note that anything from improperly sealed air ducts to a faulty thermostat could influence your heating bill. However, if you’ve scheduled routine maintenance and still notice a dramatic increase in payments, then your heating system is likely the culprit.

Furnaces naturally lose efficiency as they age, especially if they have not been properly maintained. As a result, your oil or natural gas furnace may run longer to provide the same amount of heat. Thus, your energy bills will climb.

To decide about whether you need a replacement, we recommend first comparing the cost of your recent heating bills with those from previous years. Factor in these costs with how often you’ve had to repair your furnace recently—has your technician been paying you a lot of visits? Furnaces incur the most repairs during the last two years of their lives. If you’ve had more than two furnace repairs in the last year, it’s probably time for replacement. Another way to tell if you should replace or repair is if the repair cost is over 50% the cost of a new furnace.

If these scenarios apply to you, then it’s time to replace your furnace rather than continue to pour money into a failing system.

Your burner flame is yellow instead of blue

On gas and propane systems, the burner flame should be a bright blue color (this excludes natural gas fireplaces where the flame is set to yellow for aesthetic purposes). If the flame is yellow, the cause is often a dirty burner, and the color indicates that the gas isn’t burning off completely. If your furnace isn’t heating to its full potential, then carbon monoxide could be leaking out. A common home poison, carbon monoxide is an odorless, tasteless, and colorless toxic gas that is produced whenever fuel is burned. It can be lethal in large concentrations.

Carbon monoxide can also leak out if there are cracks in the furnace’s heat exchanger, the metal panel separating the combustion chamber from the blower to distribute warm, breathable air into your home The risk for developing cracks naturally increases as the furnace ages, so it’s an ongoing problem to monitor.

Signs of carbon monoxide exposure may be frequent headaches, a burning feeling in nose or eyes, nausea, disorientation, and flu-like symptoms. Should you experience any of these, air out your house, open a window to the furnace room, and immediately call a service technician. If your family is potentially being exposed to carbon monoxide, the furnace needs to be replaced immediately.

Other possible signs of carbon monoxide include the following:

  • Streaks of soot around furnace
  • Absence of an upward draft in your chimney
  • Dripping or heavy condensation on windows, walls, or other cold surfaces (this could also mean your humidifier is set to a very high setting)
  • Excessive rusting on flue pipes, other pipe connections, or appliance jacks
  • Small amounts of water leaking from the base of the chimney, vent, or flue pipe
  • Rust on the portion of the vent pipe visible from the outside
  • Your home smells stale and stuffy, as if something is burning

In order to avoid illness or emergency, we recommend installing carbon monoxide detectors on every floor of your home, particularly close to your furnace room.

Your furnace makes strange noises

If you notice your system running louder than normal, then that’s your first indication of a malfunction, but specific sounds can help you further diagnose the issue:

  • Rattling: If you notice this sound right after your furnace turns on, that usually indicates a cracked heat exchanger, which as mentioned previously should not be ignored. In contrast, if you notice the noise a few minutes after your furnace is running, the sound is likely due to loosened screws, unsecured ductwork, or your lower furnace blower not being properly balanced. Your blower doesn’t immediately turn on when your furnace does, so that’s why you don’t hear any blower-related issues immediately when firing up your furnace.
  • Popping: With metal ducts, you’ll hear popping as they expand and contract with changing temperatures. This popping could indicate improperly sized ducts, however, which a technician could easily recognize during a tune-up. If the sound is louder than usual, then that often indicates that your furnace burner is dirty. Due to dirt buildup, your furnace will take longer to light, which causes gas to accumulate in the system as well. When your furnace ignites on delay, then that magnified popping is the sound of gas being released.
  • Humming: Your fan motor is probably going to make a bit of noise, but if it’s to the point of disruption, you might need a furnace blower motor replacement.
  • Screeching/Scraping: Aside from grating on the ears, a sound of metal scraping on metal signifies an issue with your blower wheel, which could break down your entire system if left untreated. A less severe issue could be that your blower motor is loose and scraping against its casing.
  • Squealing: These high-pitched sounds often signify that you have a loose blower belt (the bearings or pulley associated with the belt might be loose as well), or dry motor shaft bearings. These problems are easily avoidable with routine maintenance because your technician should lubricate moving parts and tighten your blower belt during a check-up. If the problem is more severe, such as a damaged blower motor or deteriorating belt, then you’ll have to fully replace the part.
  • Banging: You could have a problem with your gas ignition, meaning there is a small explosion every time your furnace ignites. This is often due to a faulty electric ignition or a dirty burner delaying the ignition. Aside from the nerve-wracking sound, you’ll want to call a service technician immediately because these explosions can crack your heat exchanger.

Another noise is when you hear the furnace blower running excessively. These noises are caused by a variety of issues like unsecured ductwork, motor failure, an unbalanced motor, or deteriorating parts. Additionally, warning signs include your blower turning on and off frequently or blowing cold air.

Making the call

It’s understandable that people often put off replacing their heating system until it breaks. After all, it can be an expensive investment, but you don’t want to risk your family’s health by putting off an impending expense. Additionally, if you’ve been relying on an older and less-efficient furnace then you’ve set yourself up for dramatic savings by making the switch. Taking the time to identify any issues is a great first step, and letting your technician take care of the rest ensures that your home will truly be the ultimate comfort on a cold winter’s night.