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3 Signs You Might Have Dirty Furnace Coils

March 17, 2023

The market for residential furnaces is worth over $7.4 billion. It’s expected to reach $12.9 billion by 2031.

Most of them are energy-efficient, with American Central Air Efficiency or AFUE ratings of 90%. That means 90% goes into the home and only 10% escapes up the chimney.

Dirty furnace coils can drastically decrease these numbers. They’ll absorb airborne contaminants instead of heat and push them through the air. This decreases indoor air quality, puts strain on your system, and can even cause it to break down.

The best way to prevent these issues is a bit of preventative maintenance. Read on to learn three important signs that you may have dirty furnace coils that need cleaning.

1. Furnace Smells

Your nose is one of your first defenses against most furnace problems. If its coils are dirty, it’ll send the scent of dust and debris into the air.

Your furnace may also try to warn you by giving off burning or gassy scents. Dirty furnace coils can contribute to these, but they can also indicate more dire issues.


Turning your furnace on in the fall after seasons of leaving it off may create a burning smell. This is usually nothing to worry about because it comes from the dust and debris it’s gathered over the year.

Regular furnace maintenance to clean the coils can prevent this smell. You only need to be concerned if it lingers for more than a few hours.

The smell of burning plastic or electrical components is more concerning. It means your furnace needs immediate service because there are issues with its internal components.

Damp or Dusty Smells

A damp or dusty smell may also arise when you turn your furnace on. This can be a sign of dirty furnace coils as their debris seeps through.

It can also hint that there’s a loose hose connection in your furnace’s drain pan. If this is the case, you’ll need a heating and cooling professional.


If you use a natural gas furnace and smell gas around it, don’t ignore it. It can come from a variety of issues, but the most common is a leak.

Turn your furnace off, get out of the house, and call an HVAC technician immediately. Exposure to natural gas can cause:

  • Headaches
  • Nausea
  • Dizziness
  • Eye or nasal irritation
  • Respiratory
  • Rashes and blisters

Rotten Egg Smell

A rotten egg smell is a sure sign of sulfur. It only seems like it’s coming from your sewer because it’s a dry sewer tap that is near your furnace.

You’ll need a plumbing professional to help with this instead of a furnace technician. It could be a sign of a serious problem with your sewer lines.

Carbon Monoxide

An odor similar to car exhaust may come from your furnace if it’s leaking carbon monoxide. A carbon monoxide detector is designed to detect this dangerous gas, even if you can’t smell it.

If yours is going off for seemingly no reason, it may indicate an issue with your furnace’s heat exchanger. They’re meant to last as long as your furnace itself, but some crack and break. The problem can be caused by:

  • A dirty or old furnace filter
  • A furnace that’s too small or too large
  • A furnace that’s short-cycling
  • Problems with the vent pipe

Annual maintenance and inspections are the best way to prevent this dangerous issue. It’s the most potentially deadly and convincing reason to keep your furnace coils clean and get regular maintenance and inspections.

2. Inefficient Heating and an Increase In Energy Bills

A furnace with a dirty coil has a longer heat time. It’ll work beyond its limits, putting pressure on the components and using up more electricity.

At the same time, it could also have shorter cycles. Turning off and on frequently can have a similar effect.

Several mechanical components may get damaged. A lack of fresh air flow can make the heat exchanger overheat and deactivate, causing shorter cycles. In addition, you could lose the:

  • Pilot light
  • Heat exchanger
  • Pressure switches
  • Gas valves

The first thing that you may notice from these issues is inconsistent heating. Dirty furnace coils will block the internal fan, making it harder for warm and cool air to pass through. That could create warm or cool spots in your home.

You’ll also notice an increase in your energy bills from these issues. Your furnace will have to work harder, and you’ll need to pay for the extra energy it uses.

The worst-case scenario is that you could have a failing furnace. You’ll have to replace expensive components or the entire system, and that’s an expensive and time-consuming process you could have avoided with a bit of maintenance.

3. Poor Air Quality

Research suggests that Americans spend up to 90% of their time indoors. This makes the risk of health issues due to pollutants greater than when they’re outdoors.

The problem is even more serious for those with allergies. At least 10% of the population is allergic to dust mites, including 90% of those with allergic asthma.

Dirty furnace coils won’t be able to properly filter out the dust and debris from the air. Susceptible family members will be forced to deal with symptoms such as coughing and wheezing.

Cleaning the furnace coils will make your home more comfortable. An air conditioning professional can help with other areas of your home to increase your overall air quality, such as cleaning out your vents.

Where to Get Your Furnace Coils Cleaned

A furnace is one of the most popular and energy-efficient ways to heat a home. They’re great when their components are clean and working well, but even a bit of dirt in the furnace coils can spell disaster.

There are several signs that you may need to wipe them off. You may notice a strange smell that won’t go away. The damage it creates could lead to increased energy bills and inconsistent heating. Your indoor air quality may also fall as built-up dirt wafts down.

Anton’s has a team of plumbing, heating, and HVAC experts. Contact us for help today.

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