If your furnace is making a rattling noise, the culprit could be something as simple as a loose screw or as serious as a cracked heat exchanger (which could be leaking carbon monoxide).
The big determining factor is whether you hear a rattling noise when your furnace turns on or if the rattling noise happens after your furnace has been running for a few minutes.
Regardless of what the issue is, you’ll want to call an HVAC pro as soon as possible.
Leaving your furnace rattling could result in expensive repairs down the road. Plus, if you do have a cracked heat exchanger, your furnace could be leaking carbon monoxide into your home, a situation that can be fatal if it's not quickly fixed.
Below, we’ll walk through these potential causes in more detail.
Want a professional to come check out your rattling furnace now? We’d be happy to help.
If you hear a rattling noise seconds after your furnace turns on…
You likely have a cracked heat exchanger
Let’s start by explaining what a heat exchanger is.
A heat exchanger is the part of your furnace that actually heats your home’s air.
The heat exchanger is a group of coils that are heated. Your home pulls in unconditioned air, and blows that air over the heated coils, transferring the heat from the coils to the air. Once the air is warmed, it’s blown into your home via your duct system.
If you have a crack in the heat exchanger, you'll likely hear a rattling noise seconds after your thermostat clicks to turn on the heat. That's because the heat exchanger is made out of metal, so when it’s heated, any cracks in it may start to expand, causing a rattling noise.
Heat exchangers can crack for a variety of reasons, including:
- Restricted airflow (dirty air filter)
- Oversized furnace
If you think you have a cracked heat exchanger, you need to contact an HVAC technician ASAP.
A cracked heat exchanger can release carbon monoxide into your home—and dangerously high levels of carbon monoxide can be fatal. Carbon monoxide is odorless and tasteless, so it’s important that you act quickly on this, because you may not realize the gas is entering your home before it’s too late.
If you hear a rattling noise a few minutes after your furnace’s blower motor turns on…
It could be the result of a variety of issues, including:
- Lose panel or screw
- Lose connections in the duct system
- Misaligned blower
Why do these issues present themselves after a few minutes rather than instantly?
Because the issues listed above are related to the blower motor and/or air turbulence—and your blower motor doesn’t immediately turn on when the furnace gets the call for heat from the thermostat.
Your blower motor waits a few minutes for your heat exchanger to fully heat up before it starts blowing air (otherwise, it’d just be blowing cool air). So if you only hear a rattling noise several minutes after the thermostat clicks to turn the heat on, you probably have one of the 3 issues listed above.
Now, let’s look at each of these in a little more detail, below.
Lose panel or screw
The simplest reason your furnace could be making a rattling noise is because of a loose panel or screw. If you recently worked on your furnace (or had your furnace worked on by someone else), this is likely your issue. Screws can also become loose over time, so even if you haven’t had your furnace worked on recently, this issue is worth looking into.
If this is your issue, start by turning your furnace off. Once the system is off, try tightening the outer panel with a screwdriver. Did the rattling stop? If not, keep reading.
Loose duct system connections
Over time, the connections throughout your duct system can become loose, and cause a rattling noise when heated air is blown through them.
There is really no way for you to diagnose this issue on your own but will require you to hire a professional to come inspect your duct system.
If this is your issue, you will need to contact a professional. An experienced tech will be able to tighten any loose connections and seal your system, to prevent heated air from escaping.
The blower is the part of your furnace that blows air over the heat exchanger and into your home’s ducts.
Sometimes, the mounts that hold the blower in place can become loose, which can cause your blower to become misaligned. If the blower motor isn’t secured properly, it can result in a rattling noise when your furnace is turned on.
If this is your issue, you’ll need a technician to come to check out your system and tighten any loose parts. This is not an issue you want to sit on. If the blower motor is loose or unaligned, it could severely damage other parts of your furnace if you continue to run your furnace.
Still hearing a rattling noise coming from your furnace? Contact Pittsburgh’s best
If your furnace is still making a rattling noise, it’s probably time to call a professional. Even if the issue is something as simple as a loose screw, it could cause damage to your furnace over time if it isn’t fixed soon.
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