What’s Not Normal For HVAC Systems (And What Is)

When it comes to HVAC systems, how do you know what’s normal or not?

Most homeowners don’t know much about their HVAC system. They know it heats and cools their home. They know it needs regular maintenance checkups and they know to change their air filters regularly.

However, what about the day to day life of the system? How do you know if what you’re experiencing with your system is normal?

Common Issues

Leaking water

Common HVAC noise and uncommon noises

Normal: If you notice a small amount of water on or around your HVAC system, that’s OK. It’s normal for your system to “sweat,” or produce water on the coils or outside of the unit. This is caused by regular condensation and isn’t cause for alarm.

Not Normal: However, if there is a large amount of water leaking from your HVAC system, whether it’s from your furnace, air conditioner, or other system component, chances are it’s not normal. It means part of your system is dripping, draining improperly, or has a leak. This can cause mold to develop, which can be damaging to your system and harmful to your home. Call your HVAC technician and have them come and take a look at your system. You may need a part replaced — or at the very least, a leak repaired.


Normal: Having a HVAC system that seems that you can barely hear or you think is “too quiet” is most likely normal. An HVAC system that is running smoothly with no problems will be quiet with only a few whooshes of air heard throughout the house.

Not Normal: On the other end of the spectrum, a system making clanking, banging, or rattling noises isn’t normal. There could be something stuck in the vent, or a part may have come loose. If not taken care of, it could damage your system. Treat the noise as a warning sign and try to find the source. It may be as simple as removing debris from a vent or from the outside air conditioner, or it may be as complicated as replacing a part. If you’re unsure, call your HVAC technician and have them come look.


Normal: In most cases a normal HVAC system that is running smoothly should have little to no odor or smell. The one time an odor is normal is at the start of the winter. When you first start your furnace back up you’ll likely smell the dust burning off of it.

Not Normal: Any kind of odor coming from your HVAC system is most likely a bad sign. If you’re smelling an electrical or burning smell, chances are something in your system has overheated. This could be caused by a dirty air filter or a wire that has gotten too hot and started to melt. Try changing your air filter, and if that doesn’t work, shut your system off and call your HVAC technician to make sure there isn’t any electrical damage to it. Not only is this costly, it can be dangerous — you don’t want any fires to start!

If the smell is more of a “dirty sock” type of smell (something earthy, musty, or stale), chances are it’s from mold that’s grown in or on your HVAC system. It could be on the evaporator coils, on the drain lines, or on the surface of system liners, and it’s caused by water on your HVAC system. This isn’t really something homeowners can address by themselves. Your best bet is to call your HVAC technician and have them come clean your system and repair the water leak. This will get rid of the mold, and also the smell.

Like any other system, your HVAC unit will have different things going on. Many small things are normal, but if you’re experiencing large disruptions, you may want to call your HVAC technician.

Have you ever encountered any of the above with your HVAC system?