Houston AC Mold: Are Filters Feeding Lung Fungus?

By Franklin Everett Shaw

August 8, 2025

You walk into your Houston home, seeking refuge from the sweltering heat, only to be greeted by a faint, musty odor. It’s not overpowering, but it’s there, lingering in the air. You might dismiss it, but in Houston, that smell could be a warning sign: mold, thriving in the humid conditions and potentially lurking within your AC unit.

Houston’s climate is a breeding ground for mold. The combination of high humidity and warm temperatures creates the perfect environment for these fungi to flourish, especially inside your air conditioning system. Your AC, while providing cool relief, can inadvertently become a mold incubator.

The problem often starts with the air filter. Many standard AC filters, especially cheaper fiberglass ones, are not very effective at trapping mold spores. These spores, along with dust and other organic matter, accumulate on the filter and inside the AC unit.

Worse, some filters themselves can become food for mold. Certain filter materials, particularly those containing cellulose, provide a nutrient source for mold growth when exposed to moisture. This creates a self-perpetuating cycle: the filter traps spores, the spores feed on the filter, and the mold spreads throughout your AC system.

So, how do you, as a Houston homeowner, combat this invisible threat? Let’s break it down into actionable steps.

Step 1: Identifying Problematic Filters

The first step is to inspect your current AC filter. Don’t just glance at it; take it out and examine it closely.

Visual Inspection: Look for visible signs of mold growth. This could appear as dark spots, discoloration, or a fuzzy texture on the filter surface. Pay close attention to the pleats and crevices, where mold is likely to accumulate.
Smell Test: A musty or earthy odor emanating from the filter is a strong indicator of mold. If you detect such a smell, even without visible signs, it’s best to replace the filter immediately.
Filter Material: Check the filter’s composition. Avoid filters made primarily of cellulose or other organic materials, as these are more susceptible to mold growth. Look for filters with synthetic fibers or antimicrobial coatings.
MERV Rating: While a higher MERV (Minimum Efficiency Reporting Value) rating generally indicates better filtration, it can also lead to increased air resistance and potentially more moisture buildup within the AC unit. A MERV rating between 8 and 11 is usually a good balance between filtration efficiency and airflow.

Common Mistake: Many homeowners in Houston use the cheapest fiberglass filters, thinking they are saving money. This is a false economy. These filters are ineffective at trapping mold spores and can actually contribute to mold growth.

Step 2: Proper AC Cleaning Techniques for Houston’s Climate

Cleaning your AC unit is crucial for preventing and eliminating mold growth. However, it’s essential to do it correctly, especially in Houston’s humid environment.

Safety First: Before you begin, turn off the power to your AC unit at the breaker box. This is a non-negotiable safety precaution.
Coil Cleaning: The evaporator coil is a prime location for mold growth. Use a coil cleaner specifically designed for AC units. You can find these at Home Depot or Lowe’s. Follow the manufacturer’s instructions carefully. Typically, you’ll spray the cleaner onto the coil, let it sit for a few minutes, and then rinse it off with water.
Drain Pan Cleaning: The drain pan collects condensation from the evaporator coil. This is another area where mold can thrive. Clean the drain pan with a mixture of bleach and water (1 part bleach to 10 parts water). Pour the solution into the drain pan and let it sit for about 30 minutes before rinsing it thoroughly.
Drain Line Cleaning: A clogged drain line can lead to water backup and increased humidity within the AC unit, creating a perfect environment for mold. Use a wet/dry vacuum to clear any clogs in the drain line. You can also pour a cup of vinegar down the drain line every month to help prevent clogs.
Professional Cleaning: Consider having your AC unit professionally cleaned at least once a year. A professional technician will have the tools and expertise to thoroughly clean all components of your AC system, including areas that are difficult to reach.

Challenge: Many homeowners are hesitant to clean their AC units themselves, fearing they will damage something. While it’s true that AC units are complex machines, cleaning the coils and drain pan is relatively straightforward. Just be sure to follow the instructions carefully and take your time.

Step 3: Mold-Resistant Filter Options in Houston

Choosing the right AC filter is essential for preventing mold growth. Here are some mold-resistant options available at local hardware stores like Home Depot and Lowe’s in Houston:

Electrostatic Filters: These filters use an electrostatic charge to attract and trap particles, including mold spores. They are generally more effective than fiberglass filters and can be washed and reused.
Pleated Filters: Pleated filters have a larger surface area than flat filters, allowing them to trap more particles. Look for pleated filters with a MERV rating between 8 and 11.
Antimicrobial Filters: These filters are treated with an antimicrobial agent that inhibits the growth of mold and bacteria. They are a good option for homes with allergy sufferers or those prone to mold problems.
HEPA Filters: While HEPA (High-Efficiency Particulate Air) filters are highly effective at trapping particles, they can restrict airflow and put a strain on your AC unit. They are generally not recommended for standard residential AC systems unless specifically recommended by a HVAC professional.

Specific Recommendations:

Home Depot: The Filtrete Healthy Living Air Filter is a popular choice among Houston homeowners. It’s a pleated filter with a MERV rating of 11 and is designed to capture allergens, bacteria, and mold spores.
Lowe’s: The Honeywell Allergen Plus Air Filter is another good option. It’s a pleated filter with a MERV rating of 11 and is also designed to capture allergens, bacteria, and mold spores.

Pitfall: Don’t fall for marketing hype. Some filters claim to be “mold-proof,” but no filter can completely eliminate the risk of mold growth. The key is to choose a filter that is effective at trapping mold spores and to replace it regularly.

Step 4: Understanding Houston’s Humidity and Indoor Mold Growth

Houston’s high humidity is the primary driver of indoor mold growth. Understanding how humidity affects your home is crucial for preventing mold problems.

Maintain Proper Humidity Levels: Aim to keep your indoor humidity levels between 30% and 50%. You can use a dehumidifier to lower humidity levels in your home, especially in areas prone to moisture, such as bathrooms and kitchens.
Ventilation: Ensure adequate ventilation in your home. Open windows and doors when the weather permits, and use exhaust fans in bathrooms and kitchens to remove moisture.
Address Leaks Promptly: Repair any leaks in your roof, plumbing, or windows immediately. Water damage is a major cause of mold growth.
Regular Inspections: Inspect your home regularly for signs of mold growth, especially in areas prone to moisture, such as bathrooms, kitchens, and basements.

Real-World Application: A homeowner in the Heights neighborhood of Houston noticed a musty smell in their bathroom. Upon inspection, they discovered a small leak under the sink. They repaired the leak and cleaned the affected area with a bleach solution. They also installed a dehumidifier in the bathroom to help control humidity levels.

Step 5: Local Professional Mold Remediation Services in Houston

If DIY methods prove insufficient, it’s time to call in the professionals. Several reputable mold remediation companies serve the Houston area.

When to Call a Professional: If you have extensive mold growth (more than 10 square feet), if you are experiencing health problems related to mold exposure, or if you are unsure how to properly remediate the mold, it’s best to call a professional.
Finding a Qualified Contractor: Look for a mold remediation company that is licensed, insured, and certified by a reputable organization, such as the Institute of Inspection, Cleaning and Restoration Certification (IICRC).
Cost Considerations: Mold remediation can be expensive, depending on the extent of the problem. Get multiple quotes from different contractors before making a decision.

Specific Examples:

Mold Remediation of Houston: This company has been serving the Houston area for over 10 years and is IICRC certified.
Advantage Pro Services: Another reputable mold remediation company in Houston with a strong track record.

Actionable Insight: Don’t delay in addressing mold problems. The longer you wait, the worse the problem will become, and the more expensive it will be to remediate.

By following these steps, Houston homeowners can take control of their indoor air quality and protect their homes from the harmful effects of mold. Remember, prevention is key. Regular maintenance, proper filter selection, and humidity control are essential for keeping your AC unit and your home mold-free.