The indoor air quality measures with real evidence behind them are, in order for a North Carolina home: keep humidity under about 55% (moisture drives mold, dust mites and mustiness); control sources (combustion, smoke, off-gassing, damp crawlspaces); ventilate deliberately (bath and kitchen fans that actually vent outside, and mechanical ventilation in tight homes); and filter better with a media cabinet at MERV 11–13; the add-ons sold at tune-ups — UV lights, ionizers, “plasma” cleaners, duct sanitising — range from modestly useful in a narrow role to unproven, and none substitutes for the first four.
1. Moisture first
Above 60% RH, mold grows on cool surfaces, dust mites thrive and the house smells musty. In our climate humidity control is IAQ: right-sized equipment, longer runtimes, sealed ducts, crawlspace encapsulation, and a whole-home dehumidifier where needed. Humidity control in NC homes.
2. Source control
Vent the dryer, range hood and bath fans outdoors (check they aren’t dumping into the attic); no unvented gas heaters; keep the garage door to the house sealed; address the crawlspace, which is the biggest hidden source in most NC houses; and choose low-VOC finishes when you renovate. Removing a source beats filtering its output.
3. Ventilation
Older homes leak enough air to ventilate themselves (with humidity along for the ride). Tighter homes need deliberate fresh air: bath fans on timers, and, in very tight construction, an ERV (energy recovery ventilator), which in a humid climate is generally preferred over an HRV because it moderates incoming moisture. Ask about it if your home is newer than about 2010 or has been extensively sealed.
4. Filtration
A 4–5 inch media cabinet at MERV 11–13 captures fine particles (smoke, pollen, dander) without the airflow penalty of a 1-inch high-MERV filter, and lasts months. HEPA in-duct systems exist for allergy and asthma households; portable HEPA units work well for a single room. Filter guide.
The add-ons, honestly
Coil UV lamp: plausible for keeping the wet indoor coil clean of biological growth in humid climates; not a whole-house purifier. Ionizers, bipolar ionization, “plasma”: independent evidence of benefit is thin, and some emit ozone or byproducts; skip unless you have specific reasons. In-duct ozone generators: no. Duct cleaning and “sanitising”: only for contamination or infestation; routine cleaning has no shown IAQ benefit (duct sealing vs cleaning). Whole-house electronic air cleaners: older units need frequent cell cleaning to keep working; media filters are simpler.
Where to start
A $15 hygrometer and a filter change this week; a look at the crawlspace and the fan vents this month; and a conversation about a media cabinet and dehumidification at your next service. Every contractor on the North Carolina registry shows the license status we found; ask what IAQ measures they’d prioritise before they show you the add-on catalogue.