In Singapore’s tropical climate, air conditioners work hard to keep our homes cool and comfortable. But if your aircon starts emitting an unpleasant smell like rotten eggs, it could indicate a serious problem that needs immediate attention.
A foul odor can stem from various causes, such as mold growth, gas leaks, or accumulated bacteria in your system. Understanding why this happens and how to fix it can prevent health risks and keep your air conditioner in top condition. Let’s dive into the common reasons for this smell and how to tackle the issue effectively.
6 Causes of Rotten Egg Smell in AC System
Cause #1 Dirty Air Filter or Evaporator Coil
Sulfur from the air can sometimes accumulate in your air conditioning system, causing a rotten egg odor. Your air filter or evaporator coil may have a buildup of dust and debris with high concentrations of sulfur. Cleaning these parts will get rid of the sulfur, and get rid of any air conditioner smells.
Excess sulfur in the air is indicative of poor indoor air quality. High concentration of sulfur in the air may appear after forest fires, volcano eruptions, or ash fall. Use an air purifier to improve the indoor air quality, and use a mask to prevent inhaling sulfur, which can irritate the eyes, lungs, and throat.
Cause #2 Mold Buildup
Certain species of mold and mildew emit sulfur or rotten egg-like smells as they colonize moist spaces. Check for damp spots near your vents, as well as mold growing in your air conditioning system. Mold may also smell like dirty socks, clammy feet, sweat, or have a musty odor.
If your air conditioner smells slightly of rotten eggs, then you may not need to call your gas company after all! The culprit may be mold colonies growing in or around your vents, which a Luce Aircon HVAC technician can remove from your air conditioning unit for good. Removing the mold will refresh your smelly air conditioner.
Cause #3 Refrigerant Leak or Gas Leak
A refrigerant leak or a gas leak is a serious problem in your home. Refrigerant is originally odorless, but manufacturers include additives into the gas to emit a foul odor, alerting the household of a gas leak indoors. A refrigerant leak would smell like rotten eggs, as does natural gas. A natural gas leak can be fatal when not addressed immediately.
Upon the first notice of a rotten egg smell, shut off all your appliances and unplug them from the socket. Open all windows and entryways to disperse the gas, and evacuate the premises before calling your gas company to deal with the leak with an immediate inspection of your gas lines. Gas may have gotten into your vents, causing your air conditioner to smell bad.
Cause #4 Dead Animal
When organic matter decomposes, it releases sulfur into the air, causing a smell like rotten eggs to emit from the decaying flesh. If you live in an area surrounded by natural habitat, or vermin crawling around, then that rotten egg odor problem may be due to an animal that died in your vents.
This is a common cause of central air conditioner smells as rodents or other vermin crawl through the centralized ventilation system, and eventually die within the air vents. The decaying animal matter gives off the rotten egg smell, which is transported through the house via the central air conditioner.
Cause #5: Clogged or Dirty Drain Pan
Singapore’s humid climate causes air conditioners to accumulate a lot of moisture, which then drips into the drain pan. Over time, if the pan is not cleaned regularly, it can collect dirt, dust, and even mold, leading to foul odors resembling rotten eggs. A clogged drain pan can also cause standing water, creating the perfect breeding ground for bacteria and fungi.
We’ve encountered cases in Singapore where homeowners experienced persistent bad odors from their AC units, only to find out that a clogged drain pan was the culprit. In some older HDB flats and condominiums, improper drainage maintenance has led to water stagnation, worsening the smell and even causing leaks.
Cause #6: Sewage Gas Seepage (Nearby Drain Issues)
In some cases, the rotten egg smell in an air conditioning system may not come from the AC itself but from nearby floor traps, drains, or plumbing issues. Singapore buildings, especially older apartments and shophouses, have floor traps and drainage systems that can emit foul-smelling sewer gases if they dry out or become clogged. When the AC is running, it can pull in these unpleasant odors from nearby drains, making it seem like the smell is coming from the unit.
How to Remove the Rotten Egg Smell from Your AC Unit?
Clean or Replace the Air Filter Regularly
A dirty air filter traps dust, mold spores, and bacteria, which can contribute to bad odors. If you run the air conditioner frequently due to Singapore's hot and humid weather, it’s even more important to clean or replace filters at least once a month. For households with pets or people with allergies, using high-quality HEPA filters can also improve indoor air quality.
Deep Clean the Evaporator Coil
The evaporator coil can accumulate mold, mildew, and dirt, leading to musty or rotten egg smells. A deep clean using an AC coil cleaner or a professional service can help eliminate trapped bacteria and prevent further odor buildup!
Inspect and Clear the Drain Pan and Drain Line
Regularly checking and cleaning the drain pan prevents water stagnation and bacteria buildup. If the drain line is clogged, it can lead to mold growth and foul odors. A simple way to maintain it is by flushing the drain line with a vinegar or mild disinfectant solution.
Check for Gas Leaks and Contact a Professional
If the rotten egg smell is due to a refrigerant or gas leak, it’s crucial to turn off the AC and seek professional help immediately. In Singapore, natural gas is commonly used in some residential and commercial buildings, and a gas leak could pose serious safety hazards. Licensed technicians can inspect the system for leaks and ensure it’s safe to use.
Remove Dead Pests and Disinfect Ducts
Pests like lizards, rodents, or cockroaches sometimes crawl into AC ducts or units and die, causing a strong, decomposing odor. If you suspect this, inspect vents and ducts for unusual smells or debris.
Use an AC-Safe Deodorizer or Disinfectant Spray
Next, to eliminate lingering odors—you can use a disinfectant spray designed for air conditioners. Spraying the intake vents and coil area while the AC is off can help neutralize bad smells before turning the unit back on.
Improve Ventilation in Your Home
Poor ventilation can trap odors inside a room, making the smell from the AC seem worse. In Singapore’s high-rise buildings, it’s essential to occasionally open windows or use exhaust fans to improve airflow. Additionally, placing an air purifier with an activated carbon filter can help absorb lingering smells and improve indoor air quality too!
Keeping Your AC Unit Clean
Schedule to clean and maintain your HVAC system with us, and trust in our technicians who will be able to provide the best upkeep services to keep your air conditioner smelling fresh and clean always! We clean, diagnose, and repair air conditioners of various models and brands across Singapore.
Contact us today to get a full list of our services!
Check out our article on why ac smells like pee!
