What Would Cause a Furnace to Overheat?

Your furnace keeps turning off and that burning smell isn’t going away. Now it’s cold outside and your house just isn’t getting warm. Unfortunately, these are signs that your furnace is overheating and unable to function as it should.

Never ignore an overheating furnace! The problem won’t go away on its own, and continuing use of your furnace can cause significant and expensive damage to your system. This can also potentially increase your risk of carbon monoxide poisoning. Read on to learn about four possible reasons for an overheating furnace and how the furnace repair technicians at Integrity Heating & Cooling can help in your Charlotte home.

what cause furnace overheat

Recognizing an Overheated Furnace

An overheating furnace loses some function and may stop working completely. You’ll probably notice something is wrong when your furnace overheats, but you may not know exactly what’s happening.

Watch for the following signs that indicate your furnace is overheating.
  • A constant burning aroma
  • A strange humming noise
  • The furnace turns off before finishing a cycle

The humming sound is a sign that your motor is working too hard. Always turn your furnace off if you hear this noise. When the furnace turns off too early, it means that the heat exchanger is at a dangerous temperature and the high-limit switch has turned off the system.

Note that it’s normal for your furnace to cause a burning aroma when it starts up if it hasn’t been on in a while. This is just the furnace burning off the dust from its components. A burning smell that lasts longer than 30 minutes or is constant is more likely caused by wires that are overheating and melting. Now that you recognize your furnace is overheating, it’s time to explore potential causes of the problem and some possible fixes.

1. Restricted Airflow

One of the most common and simple causes of an overheating furnace is poor air circulation. The internal components of your furnace can get too hot when there isn’t good airflow. This usually happens when you forget to change your air filter regularly.

The air filter traps dust and other contaminants that can clog your furnace’s ventilation system. As the filter and ventilation system become clogged, airflow is impeded, which makes the furnace work harder and get hotter.

Your furnace’s air filter should be inspected and replaced frequently throughout the year.

Here’s how often you should change your filter:
  • 1″-2″ filters: every 3 months
  • 4″ filters: every 6 months
  • 5″ filters: every 12 months

Your filter should be changed sooner than recommended if you live with many people or have pets.

2. Dirty Internal Components

When the air filter gets clogged, it allows dust and contaminants to cover the components of your furnace. The coil in your furnace can become covered with grime, preventing the heat exchanger from moving heat. The blower motor is particularly sensitive to dust and dirt; when it gets too dirty, it can’t ventilate itself and may overheat.

3. Short Cycling

Short cycling happens when the furnace turns on and off quickly or turns off prematurely in the heating cycle. Short cycling stresses your furnace motors and prevents your home from warming up. Short cycling can be caused by a few issues.

It might be caused by:
  • A furnace that is too large for your house
  • A malfunctioning thermostat
  • Overheating

In the case of overheating, short cycling occurs because the furnace is turning itself off to prevent damage to the motors. As soon as the furnace cools off a bit, it can turn back on but quickly overheat again.

4. Mechanical Failure

Failure of mechanical components in your system can cause your furnace to overheat. Electrical wiring and the fan blower in your furnace are subjected to a great deal of stress. Your furnace could overheat due to a short circuit or inadequate circulation.

Scheduling regular furnace tune-ups is the best way to make sure that the moving parts in your furnace are in good, working order. Regular tune-ups also enable technicians to spot signs of strain and premature wear. Remember that it’s cheaper and safer to repair or replace mechanical components before they fail completely and cause damage to other parts of your furnace.

How Long Does a Furnace Last?

In many cases, overheating is caused by a fairly simple issue that can be repaired. Sometimes, overheating is a sign that your furnace has just reached the end of its lifespan. At some point, mechanical failure becomes too serious or extensive to fix.

The average furnace lasts about 15 years. With regular tune-ups and maintenance, your furnace can likely last even longer than 15 years!

Depending on the cause of overheating, the solution may be a simple and affordable fix that can extend the life of your furnace. Of course, you may be left with a difficult decision: pay a lot to fix an old furnace or put the money toward a new unit instead.

A good rule of thumb when deciding whether to fix or replace your furnace is using the 50% rule. If repairs will cost more than 50% of the cost of a new furnace, opt for a new unit. By upgrading a furnace that’s 15+ years old with a high-efficiency model, you can enjoy a good return on your investment and save hundreds of dollars on heating costs.

Carbon Monoxide Poisoning: The Danger of an Overheating Furnace

A furnace that overheats prevents your home from being heated properly and has even more serious consequences. Your furnace can fail prematurely and lead to expensive furnace repair bills or even necessitate a brand-new furnace if the motor is damaged.

The most serious risk of an overheating furnace is stress cracks in the heat exchanger caused by overheating. The vast majority of premature heat exchanger damage is due to overheating as the heat stress causes cracks near the welds and bends.

You shouldn’t just be worried about a costly bill to replace your heat exchanger; these cracks can allow exhaust gases to escape into the air and your home instead of exiting the flue pipe.

That means that if you have a gas furnace, overheating can allow deadly carbon monoxide (CO) to leak into your home. CO is an odorless, colorless gas that sends about 20,000 people to the hospital each year and kills hundreds more. What’s the most common cause of carbon monoxide poisoning? Leaking furnaces and boilers.

We recommend installing a carbon monoxide detector in your home near your furnace to give you early warning if your heat exchanger becomes damaged. Your furnace should also be inspected and get a tune-up annually to spot and fix problems before they become worse.

Is your furnace overheating? After checking the air filter and checking for airflow obstructions, stop using your furnace and give Integrity Heating & Cooling a call. We offer affordable furnace repair with a lifetime workmanship guarantee in Charlotte, NC, to get your furnace back in working order. We also offer indoor air quality checks, duct sealing, and air conditioning services. Call Integrity Heating & Cooling today for more information!

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