Typical air vs. spike days
- Annual average PM2.5 (8.26 µg/m³) reflects usual daily exposure.
- Worst-day peak PM2.5 (36.64 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 Florence without contradicting EPA-aligned thresholds.
Seasonal Load and Local Factors
Seasonal pollen and mold are the primary drivers of filter restriction in this area. The proximity to the Pee Dee River basin contributes to higher humidity levels, which can facilitate mold growth if indoor filtration is inadequate. Heavy pine and oak pollen seasons create a visible layer of yellow dust that quickly coats outdoor surfaces and enters the home through every opening. This biological load settles into the pleats of your filter, reducing airflow and forcing the blower motor to work harder. In the transition months, the combination of high humidity and high pollen counts creates a sticky residue on cooling coils that can lead to efficiency loss if the primary filter fails to capture these contaminants.
Technician's Filter Recommendation
Because the PM2.5 max exceeds 25 µg/m³, I recommend a MERV 13 pleated filter for Florence homes. A standard MERV 8 or 11 filter is insufficient for capturing the fine particulates seen during the city's peak air quality events. MERV 13 filters are designed to trap smaller particles, including smoke and bacteria, which is critical when outdoor levels spike. Change your filter every 60 to 90 days. If you have pets or if the local pollen count is high, check the filter at the 45-day mark. A gray or dark appearance indicates the filter is doing its job but is nearing capacity. For households with asthma sufferers, I also suggest a standalone HEPA air purifier in the master bedroom. This dual approach ensures the central HVAC handles the bulk of the dust and pollen while the HEPA unit provides medical-grade cleaning where you spend the most time. Avoid fiberglass filters entirely; they are only designed to protect the equipment from large debris, not to clean the air you breathe.