Why Does My Air Conditioner Vent Smell Like Sewage?

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The smell of sewage coming from your air ducts can be alarming, especially when you've worked hard to keep your home clean and comfortable in Singapore. This unpleasant odor could originate from your air conditioner or external sources traveling through your air handler. Check out the common reasons for that sewer smell coming from your aircon, below!

What Causes Sewage Smell Coming from Air Vents?

The most likely reason for that sewer smell is a busted or backed-up sewer line. That sewage smell is coming from actual sewage, which is both unpleasant to smell and dangerous to your health. External factors, dirty filters, and pet waste are among other causes of sewage smells getting into your home.

Reason #1 Raw Sewage

The most obvious reason for the sewage smell is raw sewage. You may have a busted sewer vent pipe in your home, which is causing sewer gas to travel up to your air conditioner. A backed-up sewer line can accumulate waste, causing an unpleasant smell to travel through your air ducts into your home.

In some of our clients who live in Singapore's older HDB flats and landed properties, we often see cases where they experience this issue due to aging underground pipes. Over time, pipe linings deteriorate, leading to cracks or weakening that cause leaks. 

If you notice this issue in your home too, contact a licensed PUB plumber to inspect your drainage system. Additionally, ensure that your floor traps and P-traps contain enough water to prevent sewage gas from entering your home.

Reason #2 Fleeting Smells

Fleeting smells are smells that may seem like they're coming from your air conditioning systems but are actually from an external source. A burning smell may not come from your air conditioning unit, but the exhaust from cars passing by is causing the burning smell. The same goes for a rotten egg smell, sewer smell, or other AC vent smells.

If you smell sewer gas from your air duct system, but the smell passes by without lingering, then the smell is most likely from a passing garbage truck, open septic tank, or other external sources that you do not need to worry about. 

If you often experience disturbing fleeting smells, you might want to purchase a new unit. Some newer aircon models in Singapore come with built-in filtration systems that help reduce unpleasant smells from external sources.

Reason #3 Dirty Filter

Dirty filters would have more of a musty smell from mold growth, but high amounts of nitrogen, methane gas, and hydrogen sulfide gas in the air can accumulate in your damp and dirty filters, causing that sewage odor or rotten eggs smell in your air ducts. Dirty filters collect debris, dust, and dirt that latch onto odors, which may be what is causing your air conditioner to smell like rotten eggs.

Washing your air filters every two weeks is part of proper air conditioner maintenance, and will prevent any smells coming from your HVAC system. Clean the filter and evaporator coil by vacuuming it to remove the dust, and wash the filter mesh under running water and soap to deep clean it. Let the filter dry before placing it back into your unit.

Pro Tip: Consider scheduling a professional aircon servicing every 3 to 6 months, especially if you use your unit frequently due to Singapore’s hot weather.

Reason #4 Pet Wastes

Have your pets been potty-trained? Even well-behaved pets may have accidents, especially when they have not been let out to do their business. Locate the source of the smell - you might be surprised to find pet waste right next to your air vents! Grab a plastic bag to wrap up the waste, and disinfect the area with a deodorizing sanitizer.

Alternatively, you may have moved your cat's litter box closer to the vent system, which is what caused the sewage odor coming from the litter box to travel through your air ducts. In small apartments or HDB flats, the smell from a litter box can easily spread through the air conditioning system. Regularly changing the litter and using odor-absorbing sand can help prevent unpleasant smells from circulating in your home.

Reason #5 Mold Growth On Indoor Coil Drain Pan

In Singapore’s humid environment, mold growth in your aircon’s indoor coil drain pan is a common issue. When condensation accumulates in the drain pan and doesn’t drain properly, mold and mildew start to grow, producing a musty or sewage-like odor. If left unchecked, the mold can also spread to other parts of your air conditioning system, worsening the indoor air quality.

To prevent this, check the drain pan regularly and ensure the drainage system is not clogged. If you notice mold buildup, clean the pan with a mixture of water and vinegar or use an antibacterial cleaner. 

For persistent mold issues, engage a professional aircon technician to conduct a chemical wash

How to Get Rid of Sewage Smell?

Have a Professional Inspect Your Pipes

Contact a professional plumber to inspect and fix the leak in your sewage system. You may have an overflowing septic tank or a pipe that needs to be replaced. Talk to your plumber about relining or replacing your pipes as needed to get rid of the smell once and for all.

Chemical Wash Your Air Conditioning Unit

Our chemical wash service overhauls each aircon part and cleans them with a chemical cleaning solution that will refresh the components. This is especially helpful in removing the lingering smell of sewage from your aircon and will keep your aircon components from breaking down as well.

Check for a New Filter

The filter of your cooling system may no longer be effective in keeping smells away from your home. This is what causes those fleeting smells, which are a nuisance as car exhaust, garbage smell, and burning smells get into your home. Consider opting for a new aircon filter that fits the same model and brand of your aircon to keep the smells out.

Got Aircon Problems?

In Singapore’s humid climate, unpleasant smells can linger if left unchecked. At Luce, our professional cleaning services ensure your air conditioning system is fresh and odor-free. Our experienced technicians can tackle even the most stubborn smells, leaving your aircon delivering only clean and cool air.

Contact us today for more information about our services!

Check out our article on why ac smells like burning!
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