It makes sense that you’d be concerned about any new noise from your furnace. A high-pitched whistling sound could be a simple annoyance, or it could be a sign that something is wrong with the unit which needs to be fixed right away. Here are the questions to ask yourself to determine what is going on or whether the noise merits attention from an HVAC professional.
Is It a Gas Furnace?
Furnaces that are powered by a gas supply should not whistle. If they are whistling, it is possible the sound is from a gas leak at a nearby valve or within the furnace itself. Either way, gas leaks are serious, especially one large enough to be audible. If it is possible you have a gas leak, you need to evacuate the home and contact the authorities and your HVAC technician right away. While whistling is no guarantee of a gas leak, if there is a leak, it is a serious safety concern that you should always take seriously.
Is It a New Furnace?
Any new furnace will make a different sound when operating than you are used to. Still, few people describe their furnace’s operation as a whistling, it’s more like a gentle humming and the sound of moving air. Whistles from new furnaces may indicate improper installation or that an HVAC tech bumped into your ducts and created a gap which is now causing the whistling. Either way, the problem is worth a quick call to your technician. They can either reassure you that the whistling sounds like normal operation or they can investigate and find out what is causing the whistling. Just request that they actually hear the whistle before they decide how to proceed.
Is the Whistling Consistent?
Sometimes you might not be sure if it’s the air ducts, furnace, or something else making the whistling sound. See if the whistling continues if you turn the furnace off but keep the air flowing through your home. If the whistling is still happening then the problem is the more likely to be the air ducts than the furnace itself. If so, whistling air ducts usually points to a leak which can undermine efficiency but is usually simple to fix.
If you notice that the whistling seems to happen even when the furnace stops generating heat, then there may be an entirely different cause of the whistling.
Are There Other Noises?
Along with the whistle, you might hear a banging, a loud humming, a clicking, or another kind of noise. Each additional noise points to a different potential problem with the furnace, which might be more serious or require more repairs.
Look for Other Sources
It might sound silly, but just double check that there isn’t another potential source of the whistling nearby. If a kid dropped a kazoo in the furnace, left their instrument leaning against it, or left some other kind of noise-maker nearby, you can skip the call to your HVAC technician. That is, unless you can’t get the kazoo out.
