Typical air vs. spike days
- Annual average PM2.5 (8.72 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (37.31 µg/m³) is what filtration must handle during bad-air events.
Sections below reference one or both metrics on purpose — that is how HVAC vs. portable guidance differs for Louisville without contradicting EPA-aligned thresholds.
Regional Pollen and Mold Load
Seasonal allergens represent a heavy hidden load on local HVAC filters. In this region, the Ohio River contributes to high humidity levels, which facilitates mold growth and keeps heavy pollen from trees and grasses suspended in the air. These biological particles are significantly larger than PM2.5, but they are what actually clogs a filter's surface area. When the humidity rises, these particles can become damp, sticking to the filter media and reducing airflow to your furnace or air handler. If you notice your system running longer cycles without reaching the thermostat setpoint, it is often because seasonal debris has restricted the air intake.
HVAC Filter Recommendations
As a technician, I recommend a MERV 13 pleated filter for Louisville homes. Because the max PM2.5 exceeds 25 µg/m³, a standard MERV 8 or 11 filter is simply not efficient enough to capture the fine combustion particles present during peak days. Furthermore, since ozone peaks reach 0.077 ppm, you should prioritize filters that include a layer of activated carbon. Carbon is the only effective media for neutralizing ozone gas before it enters your living space. Change these filters every 60 to 90 days. If you live near high-traffic areas or have pets, check the filter every 45 days. The humidity in the area can cause filters to load up faster than in drier climates. A clean, high-efficiency filter protects your indoor air quality and prevents dust from coating your expensive evaporator coils, which maintains system efficiency.