Why is My Furnace Making a Loud Noise? A Pittsburgh Tech Answers

We’ll start off by saying that if your furnace is making a loud noise, there’s an issue with your system that you’ll most likely need a technician to fix.

But, to determine why your furnace is making a loud noise, you’ll first need to know what kind of noise your furnace is making.

Typically, we hear homeowners complaining about 3 kinds of loud noises from their furnace, including:

  1. Whistling
  2. Rattling
  3. Banging

Below, we’ll look into each of these noises in more detail, so you can determine why your furnace is making a loud noise and what the next steps are to repair it.

Want a trained expert to come to take a look at your system instead? We’re available (24/7 actually)! All of our techs are trained with at least 10,000 hours of on-the-job experience, so no matter what the issue ends up being, we can safely diagnose and fix your furnace. Learn more about the furnace repair services we offer or…

schedule a repair

Loud Noise #1: Whistling

If you are hearing a whistling noise coming from your furnace, the most likely causes are:

  1. Loose air ducts
  2. A clogged air filter

Loose air ducts:

If your air ducts aren’t properly connected and sealed, they can make a whistling noise when air is blown through them. This is because air is escaping your ducts through small cracks and holes, which can make a sort of whistling or squeaking noise when your furnace is actively blowing air throughout your home.

Loose air ducts can be the result of improperly installed ducts or can simply become loose over time. You’ll want to call a technician to come take a look at your system and tighten your duct connections. Ducts are typically in very-hard-to-reach areas, so this isn’t a fix you’ll want to attempt on your own.

Clogged air filter:

Another reason you may hear a whistling noise from your furnace is because your air filter is clogged.

Your air filter works to trap dust and debris from entering your HVAC system and circulating in your home’s air. But, if you leave a filter too long, it will get clogged and air will have trouble passing through it. If your air filter gets too clogged, you may notice a whistling noise as air tries to squeeze through the filter and into your return duct.

To fix this, turn your furnace off and check your air filter. Replace it if dirty.

Loud Noise #2: Rattling

If the noise you’re hearing from your furnace sounds more like rattling, your system most likely has a loose part or there’s an issue with the burners.

Loose part

There are many parts of your furnace system that can start to become loose over time, including:

  • Panels
  • Bearings
  • Fan
  • Motor
  • Air ducts
  • And more

If you hear a rattling noise as your furnace is running, a loose part is probably the culprit. To fix this, call a technician. If the issue really is a loose part, it should be an easy repair for a technician to handle.

Dirty burners

Over time, your burners can become dirty and clogged with soot and other debris from your furnace. If they aren’t cleaned, this layer of debris can block airflow to the burners. This produces a kind of rattling or rumbling noise.

If you haven’t had your furnace maintained in a while (1+ years), this could be your issue. You’ll want to contact a technician to take a look at your furnace and clean the burners as well as other parts of your furnace.

Loud Noise #3: Banging

Banging noises coming from your furnace are typically an indication of:

  1. Delayed gas ignition
  2. Expanding and contracting air ducts

A banging noise could also be coming from a cracked heat exchanger, but this is pretty unlikely.

Delayed gas ignition

Delayed gas ignition is what happens when your furnace doesn’t light right away.

When your thermostat calls for heat, gas is sent to your furnace. If your furnace doesn’t light right away, it causes a buildup of gas in your system, so when your furnace finally does ignite, it causes a sort of mini “explosion” which can result in a banging noise.

Delayed ignition can be caused by a variety of things, like:

  • The wrong mixture of air and gas- Your furnace needs the right mixture of air and gas to properly ignite. If there is too little or too much air or gas, it can make it hard for your furnace to ignite and cause a delayed ignition.
  • Misaligned or dirty burners- If burners are misaligned or dirty, they will struggle to ignite, causing the gas to build in your system.

Regardless of the reason for delayed ignition, if you think this is your issue, you’ll need a technician to come and take a look at your system. All of the above issues will require a professional to fix.

Expanding and contracting air ducts

Another reason you may be hearing a “banging” noise is if your ducts are expanding and/or contracting. If you hear a banging noise a few feet away from your actual furnace, this is likely your issue.

Ducts can expand near the supply side (where hot air comes out of your furnace) when there is too much positive pressure. On the other hand, they can contract near the supply side (where cooler air is sucked in) because there is negative pressure.

Expanding and contracting air ducts are usually the result of:

  • Low air supply (dirty air filter)
  • Closed or obstructed vents
  • Dirty ductwork
  • Undersized ductwork

The first step here would be to check your air filter. If it’s dirty, then you should replace it. However, if your furnace is still making banging noises, you should contact a professional. Any issues with your ductwork (including cleaning them), should be done by a professional to ensure you don’t damage your system.

Cracked heat exchanger

If you hear a banging noise right before heated air starts to come out of your vents, you could have a cracked heat exchanger. A heat exchanger is a group of metal coils, and is the part of your furnace that’s responsible for actually heating air.

If your heat exchanger overheats or doesn’t have enough airflow to it, it can crack. While this is pretty unlikely, if you think your heat exchanger may be cracked, you’ll want to call a technician ASAP. To produce warm air, your furnace burns fuel, which produces gases like carbon monoxide. If your heat exchanger is cracked, it can release those gases (including carbon monoxide), into your home.

If your furnace is still making loud noises, call Calfo’s team of pros!

Regardless of what kinds of noises you’re hearing from your furnace, we’re here to help. We have years of experience helping Pittsburgh homeowners with their heating systems and we’d be happy to help you too.