Indoor Air Quality: What Actually Matters

What is usually in household air

• Dust and dust mite debris
• Pollen, which in San Diego County has a long season rather than one sharp peak
• Pet dander
• Mould spores, where there is a moisture source
• Combustion by-products from cooking
• Fine particulate from outdoor sources, including traffic and wildfire smoke

Filtration versus purification versus ventilation

Filtration physically captures particles as air passes through a filter. Purification treats the air or surfaces to reduce biological growth. Ventilation exchanges indoor air for outdoor air. They are not interchangeable: a filter will not fix a stale house, and ventilation will not help during a smoke event.

Airflow is the part people skip

None of it works on air that never reaches the equipment. A house with restricted returns or leaky attic ducts is not filtering much of its air regardless of what filter is fitted, because a large share of what the system moves never passes through the filter at all.

Start with the cause

If the problem is a musty smell, the answer is likely a wet coil or drain rather than a purifier. If it is dust, the answer may be duct sealing rather than filtration. Diagnosing before buying equipment is the whole game here.