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Furnace Making Whistling Noise? 4 Causes (+ Fixes)

While furnaces are supposed to make certain noises, you shouldn’t be hearing any whistling sounds. If your furnace is whistling, it’s something you need to deal with to protect your furnace… and your sanity.

If your furnace is making a whistling noise, possible causes include a hole in the furnace, faulty gas supply valve, dirty furnace filter, and incorrect duct sizes. Diagnosing the problem requires a thorough inspection of your furnace system.

In this guide, I’ll walk you through the various causes for a whistling furnace explain how to fix each of the potential issues. Let’s get started!

Escaping Air Causing Furnace Whistling

One of the most common causes of a whistling furnace is air escaping through a small hole in the furnace.

Air can escape from different areas of the furnace system and cause . Possible reasons for escaping air include:

  • Duct connections have become loose
  • There is an increase in air pressure
  • The register cover is loose

Not only is this annoying, but the escaping air will decrease your heat efficiency and increase the cost of your heating bill. As such, it’s important you find and fix the issue ASAP.

How To Fix

The first thing you’ll need to do is locate the hole the air is escaping through. To do this, move along the exterior of the furnace and the pipes/ducts that are connected to the device. If the noise can be traced to a hole visible from the outside of the furnace, head to the next section to learn how to fix it.

Once you find the cause, address the issue using one of the following solutions:

  • If duct connections are loose, use the appropriate tool to fasten them. 
  • When there is too much air pressure, consider reducing the fan speed. 
  • When the register cover is loose, make sure to fasten the screws that are in place to secure the cover. 

Here’s a quick video to help guide you through the process of fixing air leaks in your furnace:

Faulty Gas Supply Valves

Faulty valves on the gas supply can also be the reason for whistling sounds. 

Remember that high pressure is applied to the gas supply. With this in mind, when the valves are damaged or loose, you may find this to be the source of this unpleasant and bothersome sound. 

How To Fix

The first step is to consider whether the valves are simply loose or damaged. The fix for these two scenarios will not be the same. Start with a visual inspection of all valves on the gas furnace. See if you can find any damaged parts.

Sometimes, you may find that the valve has come loose. In this scenario, simply use an appropriate wrench to tighten it. This should help to eliminate the whistling sound. 

If there’s a broken valve, you will need a replacement. 

When replacing a valve, be sure to turn the furnace off. You can turn it back on once the valve has been replaced. Gas flows through the valves at high pressure, which could be dangerous if you leave the system on when working with these parts. 

Be sure to take note of the valve models. There are different types and sizes when buying valves. You want to make sure the valve you buy provides a perfect fit for your gas furnace. 

If you’re having trouble replacing a gas valve, take a quick look at this video:

Dirty Furnace Filters

Filters are an important part of your heating system. Depending on the furnace model you have, there may be multiple filters used inside. As time goes by, debris, dirt, and dust all start to accumulate on the surface of your filters. This means space available for air to travel through becomes constricted. 

When there is little space available for air to pass through, pressure tends to increase. This happens when the air starts to build up behind the filter. The pressurized air passing through small gaps in the filter then creates a whistling sound. 

How To Fix

  1. Start by opening up your furnace and checking the filter.
  2. If the filter is dirty, then you may have found the cause behind the whistling. 
  3. Remove the filter and thoroughly clean it. Avoid using detergents when cleaning the filter. Instead, rinse it thoroughly with some water.

While cleaning the filter, take note that debris and other materials collecting on the filter can cause wear over the years. 

Thus, you should inspect the filter to look for damage. In this case, it might be time to get a replacement for your filter. At this point, you should consider getting a professional to help if you are not sure how to do a filter replacement. Of course, you could also check out a few videos on YouTube that show how to replace the filter. 

Not sure how to replace the filter? Here’s a video that might help:

Incorrect Duct Size

The last potential cause of a furnace making whistling sound may be related to the sizing of your ducts. Incorrect duct sizes are mostly found among furnace and heating systems that were not installed by a professional HVAC expert. Still, it is something that you should consider. 

Your ducts will be smaller with this particular situation than they should be – relative to the type and size of furnace you have installed. When the ducts do not have enough space for air to flow through, a suction occurs when the furnace is turned on. This action then leads to the generation of unpleasant whistling noise. 

How To Fix

Your initial step should be to listen to where the whistling sound is coming from. A furnace making a whistling sound due to duct size will cause the noise to come from an area where there may not be a loose valve, for example.

  1. Check the furnace model you have installed, 
  2. and then consider the ducts you have installed. 
  3. Now, consider the compatibility between the two. 

When the ducts are too small for the furnace model that has been fitted in your building, you will need to get the ducts replaced. You may find that all ducts in the furnace and surrounding system need to be replaced by larger alternatives. 

If this is the case, take precautions to ensure the new ducts you buy are compatible with your furnace. You do not want to experience the same situation once the current ducts have been replaced. 

You can watch a few videos to help you understand how ductwork for an HVAC system should be installed. Be sure to carefully inspect these videos to understand the entire process before attempting any replacements on your end. 

Below is an example of an excellent video that gives you an overview of ductwork for an HVAC system:


  • Alanna Greene

    Alanna is an avid traveler who lives in Michigan. In addition to writing for Temperature Master, he also sells crafts on Etsy and takes long walks through the forests near her home.

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