Your HVAC system is key to keeping you comfortable in your home, but it is a complicated system with multiple components. If any of the major components of your system need service, you will likely be able to tell. Knowing what an HVAC smell means can help you ensure your system stays in working order.
By paying attention to smells that come from your HVAC system and addressing them quickly, you can avoid more significant problems that could arise in the future. There are a variety of smells that can pass through your HVAC system and fill your home, signaling the need for an experienced technician. 
Burning
Chances are you have smelled a wire, or an electrical component starts to burn. Your HVAC unit utilizes a wide variety of electrical components, and if any of these are experiencing an issue, it could cause a similar burning smell. However, a unit can give off a burning smell immediately after being turned on due to dust or a dirty air filter stressing the electric resistance heaters. Before worrying about the problem, give it about 30 minutes to go away or check the air filter.
If the smell does not go away and the air filter is clean, you should look into servicing options. The first step you should take is to turn off the unit not to continue to run electricity. With a combination of motors, wiring, and switches, an HVAC unit is very complex. Therefore, if you are experiencing an electrical HVAC smell, it is best to let an experienced professional look into and resolve the issue.
Rotten Eggs
The smell of rotten eggs or sulfur is an indicator of a natural gas leak. Natural gas on its own is odorless, but local utility providers often add it to help signify a leak. If you smell this odor, you should contact the gas company and step away from your home until the issue is resolved. This may not necessarily be an issue with your overall HVAC system and more often comes from a furnace, but it is a good idea to have an HVAC technician perform a checkup to take care of the smell.
Oil
An HVAC smell of oil or smoke can indicate an oil leak that leads to burning. This is especially possible if you rely on an oil furnace to heat your home. In some cases, the problem can be quickly resolved by tightening a fitting in the oil line, tank, or filter. A more complex issue could be a malfunctioning oil burner, clogged or paired with a bad fuel pump. If the burning smell lingers for more than a few hours, you should contact a technician who will be more experienced in diagnosing the problem.
Mildew
Air conditioning units are equipped with a condensate drain to expel any water that builds up due to condensation. However, if the condensate drain is not working correctly or becomes clogged, water can quickly build up around the unit and settle for extended periods. The frozen water can lead to the growth of mold or mildew, leading to a musty smell.
Mold and mildew can also build up in other areas of your unit, especially in humid environments. Under certain circumstances, mold and mildew can begin to grow around an air conditioner’s condenser coil or in the air ducts. Of course, residue and spores from the mold will pass through the vents and spread into multiple house areas, leading to an unpleasant smell.
This unpleasant HVAC smell should be addressed by an experienced technician, who can perform the maintenance tasks necessary to ensure the unit is clean and draining properly. This includes cleaning the condenser coil and servicing the drainage components. An experienced technician can also monitor the issue to determine the extent of the problem. A technician can also discuss using a dehumidifier in your system if it may be right for you.
Residual HVAC Smell
Of course, your HVAC system is responsible for circulating air around your entire home. This means that the system will also distribute whatever is in the air. An HVAC smell may not always indicate a severe problem with your system. A plan can circulate smells like cigarette smoke, sewage, or smells from outside. Sewage smells are usually not related to your HVAC system, but they will be carried by it and should be immediately addressed by a plumber.
If the smell is unrelated to your HVAC system, you can still alleviate the odor by ensuring your system is well maintained and has a clean air filter. There are also various types of filters for a variety of environments that you can discuss with an experienced technician.
If you have any concerns about an HVAC smell, contact a trusted local HVAC technician. They can help you diagnose and solve the problem. Your HVAC system is key to your respiratory health and keeps your home at the right temperature to ensure you and your family are comfortable; don’t let problems go untreated.
Proper maintenance of your HVAC unit is also crucial to help prevent problems before they arise. Even if there is no smell, it is still essential to inspect it visually and service it regularly. Tasks like replacing the air filter and checking the wiring should be done regularly. It is often a good idea to complete an annual service to keep your unit in its best condition. Contacting a technician can help you maintain peace of mind regardless of the temperature outside.
