My Furnace Smells Funny: What To Do

Most homeowners get used to the sounds and smells of their houses. That’s why it can be alarming if you notice a weird smell coming from your HVAC system. So, what does it mean if your furnace smells funny?

Your furnace may smell funny because of moisture, dirt, dust, and debris within your air ducts. A musty odor can also appear if you haven’t replaced your air filter in 3 months or longer. Some smells, like rotten eggs and burnt plastic may indicate a gas leak or wiring problem, respectively, and require immediate attention. 

Don’t hesitate to call an emergency HVAC line if you discover an unsettling smell beyond standard mustiness. That’s especially true if your carbon monoxide detector goes off, as that is dangerous. Follow along as we explore why your furnace smells funny and highlight solutions. 

Six Furnace Smells And What They Mean

1. Dust

It’s hard to go through life without smelling a dusty furnace. This common smell is nearly unavoidable because of how much dust comes into contact with a furnace. Air filters and ducts get filled with dust and debris, and that’s unavoidable.

However, the dust can eventually reach your furnace and get burnt. The smell of burnt dust will spread throughout your house and fill the air. You can avoid this problem if you change your air filter every 3 months or sooner as needed. 

It’s also worth calling an HVAC service to clean your air ducts. Cleaning your air ducts is necessary to protect your furnace from unnecessary strain every 3 to 5 years. You can expect to spend between $350 and $1,000 to clean your air ducts, and it should stop the dusty odor. 

2. Musty Odor

Musty furnace odors typically point to a problem with the drain pan. HVAC systems have hoses that remove condensation to protect the equipment. The water winds up going to a drain pan, which can eventually become moldy and full. 

In some cases, the smell you notice is mold spreading through your house. Inspect your drain pan and see if it is overflowing or full of mold. The problem may be because the hose got disconnected from the pan, and that’s easy to fix.

Reconnect the hose and empty the drain pan to fix the problem. Otherwise, you may need a professional to clean the drain line or replace it altogether. 

3. Rotten Eggs

Nobody wants to smell rotten eggs when their furnace runs. However, this is more than a simple inconvenience; it’s an emergency. The odor you notice may point to a natural gas leak in your home.

Utility providers add a foul smell to natural gas to alert homeowners about leaks. Natural gas leaks can cause many ill effects, such as headaches, dizziness, nausea, and respiratory difficulties. First, you must call an emergency HVAC service.

Call your natural gas provider when you get off the phone with the HVAC company. Get out of the house if you feel dizzy or nauseous and wait for help to arrive. 

4. Burnt Plastic

A burnt plastic odor can indicate a furnace emergency that requires immediate attention. This typically indicates a wiring issue, which can be quite dangerous if left unattended. Many HVAC services have emergency lines that you can call for immediate help. 

Never attempt to repair wiring problems within your HVAC system unless you’re an electrician. Doing so can make the problem worse and you may suffer an electrical shock. The smell may indicate that the wires are running hot and burning the insulation in the wall. 

5. Decay

Do you notice the stench of decay when your furnace runs? You should never ignore this odor, as there is a chance that what you’re smelling is a dead animal. Small animals, like mice and squirrels, can easily get into HVAC systems through vents and gaps in the air ducts. 

Once inside, it’s hard for animals to get out, and they can die. Their bodies eventually decay and you will smell them rotting when the furnace runs. The same thing can happen when your air conditioner runs. 

You may still smell a rotten odor even if the animal doesn’t die. That’s because they may leave droppings behind in your ductwork. In that case, you must hire an HVAC service to clean your air ducts. 

6. Car Exhaust

Furnaces produce exhaust while running that they must vent to get rid of. However, this exhaust cannot safely leave your home if the pipe is blocked. That can explain why you smell something similar to car exhaust when your furnace runs. 

The flue pipe gets rid of exhaust and transports the fumes outside of your home. Unfortunately, flue pipes are susceptible to getting clogged by debris. Leaves, twigs, dirt, and dust can wind up in the flue pipe and create a blockage. 

You can even find a bird’s nest in the flue pipe in some cases, depending on its location. Call an HVAC service right away if you notice a clogged flue pipe, as it’s unsafe to inhale hazardous fumes that should otherwise leave your home. 

Does A New Furnace Have A Smell?

New furnaces typically emit a faint smell that you don’t need to worry about. This smell comes from the coating that covers many of the key components within the furnace. Some components are also covered with oils to keep them lubricated during operation.

This is normal, and it’s a sign that your new furnace is in great shape. However, you should be slightly concerned if you notice a musty odor upon getting a new furnace. That may indicate dust, moisture, and even mold within your air ducts.

Installing a new furnace won’t do anything to fix the musty smell if it’s caused by your air ducts. In that case, you must have your air ducts professionally cleaned to remove the culprit. 

Can A Furnace Set Off A Carbon Monoxide Detector?

Your furnace can set off your carbon monoxide detector, and if it does, it’s an emergency. Furnaces have heat exchangers that combine cool and warm air to maintain a balance within them. Eventually, this key component can crack and release carbon monoxide, as it’s one of the combustion gases it holds. 

Your furnace may continue to run when the heat exchanger cracks, so you may not notice right away. However, it will become apparent when your carbon monoxide detector goes off. That said, your furnace may shut off altogether when the heat exchanger cracks.

This is a very dangerous situation as carbon monoxide poisoning can be fatal. Leave the house and call an emergency HVAC line right away if you suspect that your heat exchanger is broken. Look out for symptoms like dizziness, weakness, headache, and blurred vision if you’re exposed to carbon monoxide. 

Summing It Up

If your furnace smells funny, it may be because your air filter is dirty and clogged. A rotten egg odor can indicate that you have a natural gas leak, and the scent of decay means you may have a dead animal in your air ducts. Call an emergency HVAC line if you smell burnt plastic or if your carbon monoxide detector goes off. 

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• Why Is My Furnace Rattling?
• Does A New Furnace Increase Home Value?