Quick answer
- Spring (Feb-April): oak pollen counts in Charleston regularly exceed 1,500 grains/m³ — upgrade filters before pollen season starts.
- Summer (May-Sept): humidity + closed windows + AC running 18 hours/day = focus on dehumidification.
- Fall (Oct-Nov): cooler nights, warm days create perfect mildew conditions in attics and crawlspaces.
- Winter (Dec-Jan): heating cycles stir up settled dust; replace filters monthly, not quarterly.
- Salt-air homes (within 1 mile of the coast): clean condenser coil twice a year, not annually.
Spring — pollen
Charleston spring pollen counts are among the highest in the country. Live oak, pine, and various trees overlap to produce sustained high counts from mid-February through April. If you wait until you notice symptoms to upgrade your filtration, you've already inhaled a season's worth.
Pre-season actions: change filter to MERV 11 or higher (verify your system can handle it — see the MERV guide). Schedule a coil cleaning if it's been more than a year. Verify your system's outdoor air dampers (if any) are closed.
Summer — humidity
Summer is when humidity control matters most. With outdoor RH in the 80s, every air change in your home brings in moisture. The AC removes it as it runs, but only when sized and configured correctly.
Summer maintenance: verify condensate drain is flowing freely (a clog now = flood damage in July). Confirm thermostat fan is set to AUTO not ON. Check filter monthly during heavy AC use — it loads faster than in spring.
Fall — the transition season
Cooler nights with warm humid days are perfect mildew conditions in attics and crawlspaces. The AC is running less, so it's removing less moisture, but the outdoor humidity hasn't dropped yet. This is when whole-home dehumidifiers earn their keep.
Fall maintenance: schedule the annual HVAC tune-up before heating season hits. If you have a gas furnace, get the heat exchanger inspected — CO leaks are most dangerous during the first cold snap.
Winter — dust and heating cycles
When heating runs, settled dust on ductwork and registers gets stirred up. If you've been running cooling-mode for 8 months and just switched to heat, the first week of heating often kicks up enough dust to trigger allergies.
Winter actions: change filter to start of season. Vacuum supply registers if visibly dusty. If you have a gas furnace, replace CO detector batteries.
Salt-air homes (year-round)
If you live within a mile of the coast — Daniel Island, Sullivan's Island, Folly Beach, Isle of Palms, Edisto — salt deposits build up on the outdoor condenser fins year-round. Salt-coated fins don't release heat well, which forces the compressor to work harder, which shortens its life.
Coastal-home maintenance: rinse the condenser with fresh water at least twice a year (a garden hose is fine; never use a pressure washer). Have a tech do a proper coil cleaning annually. Consider coastal-coated coils on the next replacement.
What to do next
If you've been running the same filter and the same maintenance schedule year-round, you're probably under-maintaining in one season and over-maintaining in another. A seasonal plan that matches Lowcountry conditions costs nothing and prevents most of the issues we see in homes.
Have a question about your system?
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