8 Possible Reasons Why Your Furnace Smells
Your furnace typically shouldn’t produce any odors when running. If you do notice any unusual smells coming from your furnace or your vents, it can indicate that there is some issue with your furnace or heating system. With this in mind, let’s look at the most common reasons that furnaces produce unusual odors and what to do about them.
1. Dust Accumulation
It is common for your furnace to produce a burning smell when you turn it on for the first time in the fall or any time it has not been used for a while. When the furnace sits unused, it allows dust to build up on the burners and the rest of the unit. Once it turns on and the gas ignites, this dust will quickly burn away and produce a smoky or burning smell.
If the smell only lasts for a few minutes, then you’ve got nothing to worry about. However, if the smell persists, then you will want to have the unit inspected by one of our professional HVAC technicians.
2. Furnace Is Overheating
Furnaces can also produce unusual smells due to overheating, and this problem is usually related to a clogged air filter or issues with your ductwork. If your furnace begins to overheat, you will often smell something like burning plastic or rubber, similar to what you would with some electrical problems.
This smell often indicates that the electrical wiring has started to melt due to high temperatures and is something you will want to have checked out immediately. In this situation, you should immediately turn the furnace off and leave it off until you can have a professional furnace technician inspect it. If you continue to run your furnace, it could create a major safety hazard due to the potential risk of fire.
3. Failing or Worn-Out Blower Fan
A metallic smell coming from your furnace or your vents can also indicate that the blower fan is wearing out or experiencing issues. As with the furnace itself, this smell often results because the blower is experiencing increased strain and overheating. In some cases, this smell can also result from the fan rubbing against the housing. Either way, this is another issue that you should immediately have checked out. Depending on the specific cause, the blower fan may be able to be repaired fairly simply, or you may have to have it replaced altogether.
4. Cracked Heat Exchanger
This is a much more serious issue that can potentially result in carbon monoxide being circulated throughout the building whenever the heating system runs. The heat exchanger primarily works to transfer the heat produced when gas is burned to the cold air circulating into the furnace. However, it also works to seal off the combustion chamber so that carbon monoxide and other toxic fumes can’t escape.
The most common reason that a heat exchanger will crack is due to overheating caused by restricted airflow. If there are any issues with the ductwork or the air filter is clogged, it can prevent the blower from being able to draw enough cool air into the system. This results in heat building up inside the combustion chamber and can eventually cause the heat exchanger to warp or crack.
Even though carbon monoxide is odorless, you will sometimes still be able to smell the other combustion fumes when the heat exchanger is cracked. This will usually have a strong chemical smell somewhat similar to formaldehyde which is often most noticeable when standing near the furnace. If you do smell this odor, it is essential that you leave your furnace turned off until it can be inspected.
If your heat exchanger is cracked, it will be necessary to replace it as it cannot be repaired. If your furnace is only a few years old, the heat exchanger will most likely still be under warranty. However, if the heat exchanger isn’t under warranty, it is often a better option to replace the entire furnace instead.
5. Clogged Exhaust Flue
The exhaust flue is what allows the combustion gases from the furnace to be vented outside of the home, but it can sometimes become clogged by debris or even due to birds or animals nesting inside it. If the flue is clogged, it can allow the combustion gases to escape back into the home. As with a cracked heat exchanger, this can be extremely dangerous and potentially lead to carbon monoxide poisoning.
Your furnace should automatically shut off if the combustion fumes begin to back up inside it. If this doesn’t happen and the furnace continues to run, it may produce a chemical smell, just like if the heat exchanger was cracked.
6. Gas Leak
This is another problem that can be extremely hazardous and has the potential to cause a massive explosion. Luckily, most gas leaks are fairly minor, but they are still something you should always be on the lookout for.
Although natural gas is odorless, most gas providers add a chemical to it that gives it a distinct smell similar to sewage or rotten eggs. It is normal to smell a bit of gas for a short time when the furnace first turns on. However, if the smell is extremely strong or persists for more than a few seconds, you should immediately close the gas valve to the furnace.
Once the gas is off, quickly open as many windows as you can to help the gas dissipate and reduce the chances of an explosion. You should then get yourself and any other people and pets out of the house and safely across the street. Once you’re away from the home, call the gas company or the emergency line to report the gas leak and then stay away from the house until the gas can be shut off and the leak repaired.
7. Dirty Ductwork
If you smell a moldy, musty or mildewy odor coming from your vents, it typically indicates that your ductwork is dirty and needs to be cleaned. If your ductwork isn’t properly insulated and sealed or has any air leaks, it can cause condensation to form inside the ducts. As a result, mold may start growing inside the ductwork, and the spores will then be circulated whenever your heating or air conditioning runs.
8. Clogged Condensate Drain Line
This final issue is only related to high-efficiency condensing furnaces. This type of furnace utilizes a secondary heat exchanger that allows the unit to absorb much more heat from the combustion fumes before they are vented out through the flue. As a result, the gases will cool to the point where condensation forms inside the furnace, which is then carried away and out of the house through the condensate drain system.
If you notice any musty or moldy odors when standing near your furnace, it may be that your condensate drain line is clogged. When water sits inside the drain pan or drain line, the heat from your furnace makes it easy for mold, mildew, and algae to grow.
The solution to this problem is to have one of our furnace technicians clean and unclog the drain lines. You can also help to prevent this issue and overcome any unpleasant odors by periodically using a drain pan tablet to stop mold and mildew from growing.
Professional HVAC Repairs, Maintenance and Installation
If you notice any unusual odors coming from your furnace, the team at Blue Ribbon Cooling & Heating can inspect your heating system and quickly determine the cause of the problem. We repair and maintain all types of furnaces from any manufacturer, and we also work on and install air conditioners, heat pumps and ductless mini-splits. We also specialize in indoor air quality services and install and service humidifiers, dehumidifiers, air purifiers and air filtration systems. Give Blue Ribbon Cooling & Heating a call today if you need your furnace inspected or any other HVAC service in Round Rock, Bastrop or the surrounding areas.