Your heating system will always be louder than your air conditioning, as gas furnaces make quite a bit of noise when they run. However, if you hear any whistling or other unusual noises whenever your furnace is running, it indicates some issue preventing your heating system from working properly. With that in mind, here is a full overview of why furnaces sometimes whistle and what issues can cause this.
What Causes a Furnace to Whistle?
Many people wrongly believe that hearing whistling noises whenever their heating system is running is a sign that there is some issue with their furnace. The truth is that whistling noises generally have nothing to do with the furnace itself and are caused by an airflow issue related to the duct system. In most cases, whistling noises mean that either air is escaping from your ductwork somewhere or the airflow in the return ductwork is restricted for some reason.
Air Escaping From the Ductwork
Your ductwork is a closed system designed to circulate hot air from the furnace into each homeroom. If your ductwork is damaged, some air will always leak out. This will also happen if the connections between the ducts are loose or the duct tape no longer seals the links tightly. Ductwork can also degrade with age and slowly start to develop leaks. If your ductwork leaks, the blower fan forces air out through any holes or gaps. As air is forced out of the ducts, it often produces a loud, high-pitched whistling or squealing sound.
Air leaks are widespread if your ductwork is more than 20 years old. Leaks will often also occur if you have recently had your blower fan replaced or repaired. In this situation, the new or repaired blower will suddenly force much more air through the ducts than before. This increased air pressure can sometimes cause the duct connections to blow out or create gaps in the ducts. You will also hear a louder whistling sound since more air is now being forced out of the gaps than before.
The solution to any of these issues is to have your ductwork inspected, repaired, or resealed. If your ductwork is quite old and not in great shape, you may need to replace it to prevent it from leaking.
You may also hear whistling if too many of your supply vents are closed, clogged, or obstructed. If air doesn’t flow out of all of your vents, it leads to an increase in air pressure inside the supply ducts. This increase in air pressure can force the air out of the open vents with such force that it makes a whistling sound and will also force the air out of any holes in the ducts. The best way to prevent this issue is by ensuring that your vents aren’t obstructed and keeping at least 75% of the vents fully open.
You can also hear a whistling noise coming from your ductwork or vents due to an issue restricting how much air the blower fan can draw in through the return vents. The most common issue leading to restricted airflow is a dirty air filter, which is why you must replace your air filter at least every one to three months. If you don’t replace the filter regularly, it will quickly become clogged so that very little air can flow through it. If the airflow is restricted, it puts a huge amount of strain on the blower fan and will limit the effectiveness of your heating system and increase your energy bills. You will also often hear a loud whistling noise as the blower tries to draw air in through the filter.
If your return air vents are clogged with hair and debris or obstructed by furniture, the blower fan will also reduce how much air can draw in and sometimes produce a whistling sound. This problem can easily be overcome by cleaning the return vents and ensuring nothing is blocking them.
At O'Brien Heating & Air Conditioning, our team can help if your heating system is whistling or having any other issues. We can assist with duct cleaning, resealing, repairs, and installation, and we also repair, maintain, and install furnaces, heat pumps, air conditioners, and water heaters. So if you’re experiencing any issues with your heating system or need any HVAC service in the Drexel Hill area, give us a call today.