An HVAC system is manufactured with certain standards in mind and are the result of meticulous adherence to national, state, and local guidelines. The system in your home or building is the culmination of years of advancements in the conditioning of air and how to use that air for your convenience. In addition, dwellings and buildings have become more air tight causing them to require ventilation designs that allow for the movement of air from the inside to the outside and around the inside of the dwelling.

However, mechanical parts and electrical systems have an inherent limit to their length of life, endurance, and maintainability over time. The second law of thermodynamics expresses the fact that in any closed system, the total entropy(disorder) of it will increase over time. In other words, things are always headed toward disorder and chaos as opposed to order and organization. This explains why things are always in need of repair and maintenance.

NOTE: If you are turning on the heat and you smell something burning, it may just be your furnace or heat pump burning off dust. If you are using the AC for the first time, it is likely something is overheating.

Electrical Smells

It is possible that sometimes when you turn on your HVAC system it smells like something is burning. These types of smells are HVAC odors. Well, something is most likely actually burning or has burnt and you are smelling the result. The system’s motors or the electrical wiring could be the issue here. If left unattended, the area burning could progress to a full burn. This would be catastrophic for your system and possibly for your home.

Remember that electrical wires are coated with either rubber or plastic and if not connected properly or there is a surge in electricity causing a burnout, then you may be smelling these insulators. If, for instance you have not replaced the filter in a while, the motors in your HVAC system may be working too hard and calling for more current than is really necessary. This call for excessive electrical current will cause a thermal increase, resulting in a burn.

If you detect the smell of electrical connections or wires, shut off the power to your unit and contact a professional HVAC service provider.

Fan Belt Smells

Another area of concern closely related to electrical burn smells are rubber smells that emanate from a loosely fitting or worn out fan belt. As time passes, fan belts can expand, crack or dry out. These will have to be replaced and it is best to let a professional do it.

If you smell electrical burns or the smell of rubber, turn the master shutoff switch to off and call a professional.

Mold or Musty Smells

Inside your HVAC unit, there are places where condensation will accumulate and moisture is building up. Mold requires a food source, darkness, moisture, and warmth. The inside of the HVAC system is a perfect location for mold to grow.

Condensate drain pan or line: When condensation forms on the evaporator coil it eventually finds its way to the drain pan and down a drain line. If this drain is clogged the water will back up and stagnate in the drain pan. The drain will have to be unclogged and the drain line along with the pan must be cleaned.

Air Ducts: The duct system routes the air flow. Over time, these ducts can begin to leak. If this happens, they will allow the outside air to infiltrate your home or office space. This air will contain contaminants, dirt, dust, and mold spores. These spores will grow and populate your HVAC system.

Motors and Capacitors

Motors have mechanical parts that are machined to tolerances that assist the motor to maintain its credibility and use. They contain bearings that can wear out causing it to overheat. They will emit a burning odor should deterioration set in.

Some capacitors assist the motor to start during system startup while others assist the system to maintain its running during a cycle. The capacitor powers the motor. Capacitors break down due to usage and power surges that happen over time. When the capacitor fails, it must be replaced. This is best done by an HVAC professional.


The final odor that must be mentioned is the possibility of smelling a gas. A smell of gas must be taken seriously. If you are smelling this chemical, then the course of action would be to open your windows and ventilate the area. After this, you want to leave the house and call your gas provider.


One of the best ways to prevent odors inside your home is to perform regular maintenance checks on your HVAC system. Also, you might consider a yearly maintenance contract to keep your system tuned up and parts within warranty. The odors mentioned here can mostly be taken care of quickly by early detection.