Indoor Air Quality in San Diego Homes: Filtration That Can Be Measured

Indoor air quality is sold with a lot of hype. Our position is simpler: the HVAC system moves all of the air in your house several times an hour, so the filter it passes through, the ducts it travels in and the fresh air it mixes with decide most of what you breathe. Get those right before buying a device.

Media filter cabinets (MERV 11–13)

The standard 1-inch filter slot on a San Diego furnace holds a filter that is either too coarse to catch fine particles or too restrictive when it does. A 4–5-inch media filter cabinet installed at the return of the air handler holds a deep pleated filter with many times the surface area. At MERV 11–13 it reduces airborne particulates, including fine smoke particles, pollen and pet dander, while keeping airflow resistance low enough for the blower to run normally. Filters last months rather than weeks. On every install we measure static pressure before and after to confirm the system is not straining.

Wildfire smoke seasons

Santa Ana events in the fall push smoke across the county, and the smell gets into homes from Escondido to the coast. During those days the system should run the fan continuously with a MERV 13 filter in place, windows closed, and any fresh-air intake temporarily shut. A variable-speed blower that can circulate quietly at low speed makes continuous filtration practical rather than noisy. We set this up as part of the filter cabinet installation.

Filtration vs. purification

Filtration removes particles from the air stream; it is rated (MERV), tested and predictable. Purification products, including UV lamps at the coil, ionizers and photocatalytic units, work on different targets, and their real-world performance depends on the product, the airflow and how they are installed. Some ionizing products have raised concerns about byproducts. We install filtration because its effect can be measured, and we discuss purification only when a specific problem calls for it. We do not make health claims for either beyond what they do to airborne particulates.

Ventilation basics

Newer, tighter homes and remodels in San Diego are built to a ventilation standard that brings in outside air deliberately. Older tract homes leak enough that they ventilate themselves, but bathroom and kitchen exhaust still matters for moisture and cooking byproducts. We check that existing exhaust fans actually vent outside (many dump into the attic) and, on tighter homes, that the fresh-air intake is filtered and controllable.

Humidity in coastal homes

Coastal Zone 7 homes under the marine layer in Encinitas, Pacific Beach and Coronado run damp in late spring and early summer, which shows up as musty closets and condensation on uninsulated ducts. The fix is usually not a dehumidifier; it is sealing and insulating the ducts, running the AC long enough to dehumidify (an oversized system short cycles and never does), and venting bathrooms properly. Inland Zone 10 homes have the opposite problem in the fall and rarely need humidity control.

Our position on duct cleaning

We evaluate ducts before recommending anything. In most San Diego homes the dust problem is return-side leakage pulling attic air and insulation fibers into the system, or a filter that is bypassing around its frame. Sealing or replacing the ducts and fixing the filter path solves that; cleaning dirty ducts that still leak solves nothing. Cleaning has a role after water damage or construction, and we will say so when it does.

What to install during a changeout

When you replace an air conditioner, furnace or heat pump, the air handler is out and the return is open. That is the moment to add the media filter cabinet, enlarge the return, seal the ducts and specify a variable-speed blower. Doing it later means opening things up twice.