Your HVAC system can tell you that there's something going on with it in a number of ways. It can start to make noises, it can start being unreliable, or it can start to put out a number of odors. Many times, you will be able to figure out what's wrong with your system by paying attention to the smell coming from it. Here are some of the different smells you might notice and what they might be telling you about your system.
There is a musty smell
If you notice a musty smell, then this is a sign that you are dealing with an issue where there is mildew or mold somewhere inside of the system. This is concerning because mold can be hazardous to a person's health. Those most at risk will be anyone with respiratory issues, but mold can be hazardous to anyone's health. Mold can be anywhere in the system where there is dampness. If you aren't sure what a musty smell is, you can relate it to that of a dirty laundry basket. Since there are so many places mildew or mold can be within the system, you want to call an HVAC tech out to help you locate the issue if you aren't able to locate it on your own.
There is a dumpster smell
A dumpster smell—like when there is rotten meat that has been thrown away—means that you have something dead in the ductwork. Even a mouse can create a horrible smell when it is in the duct decomposing with the air being pushed past it and then pushed out of the vents. If you have this smell in your home, then you want to have an HVAC tech come out to remove the dead pest from the ducts. Then, you can have them better secure the areas where the pest may have entered into the ductwork from so this type of thing will be less likely to happen again.
There is a burning smell
If you smell burning, like burning wires, burning plastic, or any other type of burning smell, turn the system off immediately. Be prepared to have the fire department come out if need be. Put an emergency call in to a residential heating tech letting them know what the issue is so they will know to make you a top priority. Do not turn the system back on until after someone has come out and addressed the issue for you. Note that you will smell a hot and dusty type of odor the very first time you turn the heater on for the season. However, the smell will quickly fade as the hot dust is blown out of the ducts.