It takes a few minutes for the fan of a furnace to finally start that familiar whir sound. That’s because it takes a few minutes for the furnace plenum to actually heat up after the burners light, and the fan does not start running until it is warm enough to deliver air to the vents in your home. Once you do hear that spinning, whirring blade and the rush of air through the vents, it’s a satisfying sound—unless it’s accompanied by an unfamiliar noise.
Other than the sounds you are familiar with as your furnace starts up, you should not expect to hear much else as the system runs. If you notice noises from the vents or the unit itself, it’s usually time to call in technicians. Here are 4 of them you cannot afford to ignore.