When Should You Replace Your Furnace? (5 Warning Signs)

Figuring out when to replace a furnace is not as straightforward as it initially seems. Without experience working on HVAC systems, how are you supposed to tell whether or not those strange noises emanating from your furnace are a problem?

We put together this handy guide to help you troubleshoot your furnace problems and decide if you need to replace your furnace — or if you can get by with a simple repair. If it turns out that you need to replace your furnace, we encourage you to get several quotes from the best HVAC companies in your area before making your decision.

What are the Signs It’s Time To Replace Your Furnace?

Diagnosing your furnace’s health before it fails is essential for avoiding the headaches and expenses of needing an emergency furnace replacement. If you’re unsure whether or not your furnace is on its last legs, Here are the five most common ways to determine the ideal time for furnace replacement:

• It’s getting old.
• It needs more frequent repairs.
• There’s a noticeable increase in your energy bill.
• It heats your home unevenly.
• It makes unusual noises.

It’s Getting Old

Even if your old furnace isn’t showing negative signs, you’re better off not waiting until it fails to consider getting a new one. We know this sounds like generic advice, but keeping your furnace’s age in mind can help you detect that it’s failing faster than you otherwise might.

If your furnace is more than 15 years old, small warning signs carry more weight — including more frequent or longer runs to reach your desired temperature. Most furnaces don’t fail suddenly without warning, so it’s possible to predict their failure if you’re paying attention.

More Frequent Repairs

A string of furnace repairs is annoying and expensive, but it might be more than just bad luck. As furnaces age, their components wear out — leading to repeat visits from your neighborhood HVAC contractor.

Furnaces last between 15 and 25 years on average, but individual components may start to fail earlier. Here are some common furnace repairs you might encounter as your furnace ages:

• Blower Motor: If your blower motor isn’t working properly, your furnace won’t have the airflow needed to heat and circulate air throughout your home. Even worse, a struggling blower motor strains other parts of your furnace — which can lead to a cascade of issues.
• Cracked Heat Exchanger: This is an emergency that requires immediate repair. A cracked heat exchanger could release carbon monoxide into your home, so you should call a professional HVAC tech immediately if you suspect your heat exchanger is compromised. Unfortunately, replacing the entire furnace is often more cost-effective since repairing the heat exchanger is very expensive — when even possible.
• Ignition: It’s common for a furnace’s ignition system to experience issues as the furnace ages. Cycling on and off more frequently than normal or not turning on at all is a telltale sign that your furnace’s ignition system is faulty.
• Thermostat: Your thermostat is the brain of your entire HVAC system. A bad thermostat can cause your furnace to turn on more or less frequently, so it can be hard to tell when it needs to be replaced.

Furnaces will encounter problems that require repairs throughout their lives, but several issues in a short period could indicate a more systemic problem.

Noticeable Increase in Your Energy Bill

One of the earliest signs that your furnace could be starting to go is a steady increase in energy costs over a few months. As furnaces age, their energy efficiency decreases, meaning they need to work harder to keep your home at a comfortable temperature. This efficiency reduction is mostly due to ordinary wear and tear but could be exacerbated by neglecting regular maintenance.

Before you run out to replace your furnace, it’s worth checking a few things first:

• Check for leaks: Leaks can make your furnace work harder than normal. Have a licensed furnace maintenance technician inspect your furnace for leaks before you decide it’s time for a replacement.
• Ensure proper furnace ventilation: Furnaces need good ventilation to operate efficiently. If your furnace is situated where its vents may be unintentionally obstructed, such as a basement or attic, inspect the area to confirm that no items have been inadvertently placed in front of the vents.
• Replace the filter: Furnace filters must be replaced every three to four months. If your filter is old and full of dust or debris, it could cause an airflow blockage, which requires your furnace to expend more energy to keep the air circulating. Replacing the filter helps with energy efficiency and improves indoor air quality in your home.

Aging windows and doors can also lead to increased utility bills due to leakage, so be sure to check those, too.

Uneven Heating

Another sign that your furnace might be on its way out is that it no longer heats your home evenly. Uneven heating is often a symptom of duct issues like leaks or blockages. Your HVAC tech should be able to narrow down where there’s likely a problem based on what rooms aren’t receiving enough heat. Issues with the main duct are usually harder to locate since they affect the entire system, but a quick inspection is usually enough to tell there’s a problem. If the ductwork checks out, it could be an issue with the filter or blower motor.

Unusual Noise

Unusual clunking, rattling, or popping sounds could indicate that your furnace is not long for this world — or it could be a minor issue that’s easily fixable, like a loose screw or panel. Let’s go through a few different types of sounds and discuss their most likely causes:

• Popping/Banging: These sounds are difficult to assess and could stem from several issues. Benign causes of popping include expanding and contracting ductwork and clogged vents. Banging sounds could also be caused by more serious problems, like a cracked heat exchanger or malfunctioning blower motor.
• Rattling: Rattling is often a sign of a loose screw, panel, or some other physical part of your furnace. If you can locate the loose piece, resecuring it will often resolve the problem and eliminate the sound.
• Squealing: A more serious sound is squealing, which is almost always caused by a worn fan belt. You should turn your furnace off and call a technician if you hear squealing to avoid damage to your furnace’s blower motor.

If you can’t locate the issue after a quick inspection, contact an HVAC professional. Any changes in your furnace’s behavior could indicate that it’s approaching its end of life — especially the sudden onset of unusual noises. More serious problems don’t necessarily mean you’ll need to replace your entire furnace, but you should consult an experienced technician to find out.

When Should You Replace Your Furnace by Type?

The symptoms of an aging furnace are largely the same between different fuel types, and you can use the information from the previous section to decide whether or not it’s time to purchase a new one.

Not all furnaces are created equally; some have longer average lifespans than others. Electric and natural gas furnaces typically last between 15 and 20 years, while oil furnaces can last up to 25 years if well-maintained. The tradeoff is that oil furnaces often cost more.

The following table summarizes the different types of furnaces to help you decide which is right for your home.

Should You Repair or Replace Your Furnace?

If you or your HVAC technician think that an issue is isolated to a single component, you might be able to get away with repairing or replacing just that component instead of the entire system. Of course, you don’t want to wind up in a situation where you replace a new piece of the system every three months until you eventually need a new heating system.

Another consideration is the repair costs. Springing for a $1,000 to $1,500 repair doesn’t make sense when a brand-new furnace may cost only slightly more.

If you decide to replace your furnace rather than try to repair it, the best HVAC companies will use your home’s size, window placement, and interior room layout to help you choose the right system for your home and energy needs — including air conditioning options if needed. They may even recommend purchasing a heat pump or another combined heating and cooling system to save money on replacement costs.

Check out the video below to see how the process might go.

Planning to replace the furnace? Check out our guide to the top furnace brands to choose from.

What’s Our Recommendation for When To Replace a Furnace?

We’ve thrown a lot of information at you in this article, so let’s take a step back and simplify things. If your furnace can no longer heat your home effectively, it’s time for a new one. That could mean uneven heating, inefficient heating that leads to high monthly heating bills, or inability to produce enough heat.

Most furnaces end their useful life after 15 to 20 years. If your current furnace is around or above that age and you start noticing it showing one or more of the above signs, you should contact your local HVAC companies and start surveying your options.