Longer Allergy Seasons Make Fall HVAC Checks More Important

# Why fall matters for indoor air

Cooler outdoor temperatures don't automatically mean relief for people with allergies. Weed pollen, especially ragweed, often peaks in September and October. Wet conditions and decaying leaves also drive mold spore levels in the same period. A later first frost—about 10 days later than 30 years ago, according to the Asthma and Allergy Foundation of America (AAFA)—lengthens that window.

# How building transitions affect allergen exposure

People and pets can carry pollen and spores indoors on clothing, hair, and fur. That means indoor exposures can rise even after windows are closed.

# Filtration: pick the right filter for the system

• MERV 13 filters capture finer particles including pollen and pet dander, and are a common recommendation for better particle capture.
• Filter performance depends on more than MERV rating: pleat geometry, surface area, design, and how the filter fits the system all affect resistance and capture.
• Pressure drop matters. Use the most effective filter the HVAC system can accommodate without restricting required airflow or reducing runtime.

Contractors should evaluate each system's airflow requirements and select filtration that balances particle removal with acceptable pressure drop.

# Operational and maintenance steps for fall

• Maintain circulation. HVAC systems reduce airborne allergen concentrations only when air moves through the filter.
• Review ventilation strategy as heating begins. Reduced fresh-air intake or closed dampers can raise indoor concentrations if particles are already inside.
• Watch humidity. Fall's wetter conditions and decaying organic matter can increase indoor mold concerns if humidity rises indoors.

# Who should act and how

Contractors: use fall tune-ups as an opportunity to discuss IAQ with customers. Assess filter compatibility, airflow, and the need for higher-performing filtration where outdoor particle loads are elevated.

Facility managers and homeowners: treat fall as a second IAQ check after summer. Replace filters, monitor airflow and humidity, and consider higher-efficiency filters only if the system can handle them without airflow loss.

# Local air quality context

Areas with poorer outdoor particle pollution have added reason to prioritize filtration. The article cites Lehigh County receiving a D for short-term particle pollution in the American Lung Association's 2026 report, illustrating how outdoor conditions can influence indoor decisions.

# Bottom line

Longer pollen and mold seasons make fall more than a seasonal switch. Practical HVAC checks—right filter selection matched to system capacity, routine filter changes, and attention to airflow, ventilation, and humidity—reduce indoor allergen exposure at a time when outdoor allergens persist later into the year.