Indoor air quality (IAQ) is what you’re actually breathing inside your house. It includes particulates (dust, pollen, smoke), gases (carbon monoxide, VOCs from furniture and cleaning products), humidity, temperature, and biological contaminants (mold, bacteria, pet dander). The EPA estimates indoor air is 2-5 times more polluted than outdoor air in most homes, and sometimes 100 times worse during specific events.
In San Diego, IAQ is shaped by three factors specific to our climate: wildfire smoke during fire season, marine layer humidity in coastal areas, and the dust-heavy dry inland summers. Here’s what matters and what’s worth doing about it.
What “indoor air quality” actually measures
Five categories of measurable air quality factors:
1. Particulate matter (PM2.5 and PM10). Tiny solid particles. PM2.5 (under 2.5 microns) is the most health-concerning because it bypasses your respiratory system’s defenses and enters your bloodstream. Sources: cooking, dust, smoke, pollen, exhaust.
2. Carbon monoxide (CO). Odorless, colorless, lethal in high concentrations. Sources: gas appliances with cracked heat exchangers, idling cars in attached garages, blocked flues.
3. Volatile organic compounds (VOCs). Chemicals that off-gas from furniture, paint, cleaning products, building materials. Long-term exposure is linked to respiratory issues, headaches, some cancers.
4. Humidity. Both too low (under 30% relative humidity) and too high (over 60%) cause problems. Low: respiratory irritation, static, dry skin. High: mold growth, dust mite proliferation.
5. Biological contaminants. Mold spores, bacteria, viruses, pet dander, pollen. Visible mold means there’s already a moisture problem; invisible mold is more common and harder to address.
San Diego-specific air quality patterns
Five patterns particular to our region:
1. Wildfire smoke season (October-December typically). Even fires hundreds of miles away can push PM2.5 levels in San Diego to 5-10x normal. The 2025 fire season pushed indoor PM2.5 to 200+ in homes without air filtration during peak events. AQI levels above 150 are considered unhealthy for sensitive groups.
2. Marine layer humidity (May-July). Coastal homes (within 5 miles of the ocean) see indoor humidity climb to 65-75% during morning marine layer. Sustained humidity over 60% is mold-friendly. Coronado, La Jolla, Encinitas, Carlsbad, Oceanside see this regularly.
3. Inland dust loading (June-September). Dry inland summers throw fine particulate into the air. Escondido, El Cajon, Santee, Lakeside homes see filter loading 2-3x faster than coastal homes during summer.
4. Pollen waves (February-May for trees, late spring for grass). California-specific pollen patterns mean asthmatic and allergic residents see indoor symptoms even when staying inside if HVAC filtration isn’t catching the loads.
5. Vehicle exhaust in urban corridors. Homes near I-5, I-805, I-15 see elevated particulate from highway traffic. PM2.5 levels can stay 30-50% above background even with windows closed.
What ACTUALLY improves indoor air quality
Five interventions ranked by cost-effectiveness for San Diego homes:
1. Better air filter. The single biggest IAQ improvement for most homes. Replace fiberglass filters with MERV 11-13 pleated filters. Cost: $20-$60 per filter, $80-$240/year. Improvement: 60-80% reduction in PM2.5 and PM10 inside.
2. Filter change frequency. Most homes underchange filters. In San Diego, change 1-inch filters every 60 days (not 90), 4-inch media every 6 months. During wildfire smoke events, check weekly.
3. UV light air purification. UV lamps installed in the air handler kill mold spores and bacteria as air passes through. Cost: $400-$900 installed. Useful for coastal homes with humidity-driven mold concerns.
4. Whole-house electronic air cleaner. Higher-end filtration that goes beyond what disposable filters can do. Cost: $700-$2,000 installed. Most useful for homes with severe allergies or respiratory conditions.
5. ERV or HRV (energy/heat recovery ventilator). Brings in fresh outdoor air through a heat exchanger that recovers the energy that would otherwise be lost. Cost: $1,500-$4,000 installed. Most useful in tightly sealed newer homes; less common in older San Diego homes that already infiltrate plenty of outdoor air.
What we DON’T recommend: portable plug-in “air ionizers” that produce ozone (can worsen respiratory issues), expensive proprietary systems with no measurable performance data, and most marketing-driven “air purifier” products sold without specific filtration ratings.
How to measure your indoor air quality
Three options ranked by cost:
1. Visual + smell check (free). If you see dust accumulating on flat surfaces between weekly cleanings, smell mustiness in any area, or notice pet odors that visitors mention, your IAQ has measurable problems.
2. Consumer IAQ monitor ($150-$400). Devices from Awair, Airthings, IQAir, or Atmotube monitor PM2.5, VOCs, humidity, temperature, and CO2 continuously. Useful for ongoing tracking and identifying problem times of day.
3. Professional indoor air quality test ($300-$700). Used when there’s a specific concern (suspected mold, recent water damage, respiratory illness with no obvious cause). Includes lab analysis of air samples. Most useful as a diagnostic tool, not for routine monitoring.
For most San Diego homes, a $150-$200 consumer IAQ monitor combined with proper filter changes solves 80% of the problem.
What CO monitoring should look like
Separate from general IAQ: carbon monoxide is acutely dangerous and requires its own dedicated monitoring.
- Install CO detectors on every floor, especially outside bedrooms. California Code requires them in any home with gas appliances. Cost: $25-$60 per detector.
- Replace CO detectors every 5-7 years. The sensors degrade. Old detectors won’t alarm even at dangerous CO levels.
- Schedule annual furnace maintenance that includes combustion analysis. A cracked heat exchanger can dump CO into your air without producing any other symptoms.
If a CO detector goes off, evacuate the house immediately, call 911 or SDG&E at 800-411-7343, and don’t re-enter until the source is identified.
What we recommend for typical San Diego homes
Tiered by household need:
Standard household, no respiratory issues: MERV 11 pleated filters changed on schedule (60 days for 1-inch, 6 months for 4-inch). Annual maintenance visit. Total: $200-$300/year incremental cost.
Coastal household with humidity concerns: Above + dehumidification add-on or UV light in the air handler. Total: $400-$1,200 one-time + $200-$300/year.
Household with allergies or asthma: Above + MERV 13 filtration (verify your system can handle the airflow restriction) + consumer IAQ monitor. Total: $500-$1,400 one-time + $250-$400/year.
Household with respiratory illness or pregnancy: Above + whole-house electronic air cleaner or HEPA filtration in main living areas. Total: $1,500-$3,000 one-time + $300-$500/year.
Household in fire-prone areas (East County, Backcountry): Above + dedicated portable HEPA units for bedrooms during fire season. Total varies; portable HEPA units run $200-$500 each.
For more detail on what we install and recommend, see our indoor air quality service page.
FAQs
What is indoor air quality (IAQ)?
Indoor air quality refers to the quality of the air inside buildings and structures, especially as it affects the health and comfort of occupants. Includes particulate matter, gases, humidity, and biological contaminants.
Why is indoor air quality important?
Most people spend 80-90% of their time indoors. Indoor air is typically 2-5 times more polluted than outdoor air. Poor IAQ contributes to respiratory issues, allergies, headaches, fatigue, and long-term health problems.
How can I test the air quality in my home?
Three options: visual/smell inspection (free, limited), consumer IAQ monitor ($150-$400, ongoing data), or professional air quality test ($300-$700, diagnostic for specific concerns).
What’s the best air filter for indoor air quality?
MERV 11-13 pleated filters offer the best balance of filtration and airflow for most residential HVAC systems. MERV ratings above 13 may restrict airflow too much for some systems; verify with your installer before going higher.
How often should I change my HVAC filter in San Diego?
1-inch filters: every 60 days. 4-inch media filters: every 6 months. During wildfire smoke events: weekly checks. Inland homes during dust-heavy summers may need 45-day changes.
Do air purifiers actually work?
Quality whole-house electronic air cleaners and properly sized HEPA units in individual rooms do measurably improve IAQ. Cheap plug-in “ionizers” that produce ozone are not recommended and can worsen respiratory issues.
Is the air in my San Diego home safe to breathe?
For most homes, yes, but with measurable particulate from outdoor pollution, dust, and seasonal smoke that filtration improves. Coastal humidity can support mold; inland dust loads filters faster. Annual HVAC maintenance + appropriate filtration handles 80% of typical IAQ concerns.
What is the most important thing for indoor air quality?
Two things tie: filter quality (MERV rating) and filter change frequency. Most other IAQ improvements are layered on top of those basics. A premium air purifier with a clogged main system filter won’t help much.
When to call us
If you’re dealing with allergies, mold concerns, or wildfire smoke impact and want to know what would actually help, we’ll assess your specific situation. Call (442) 777-6440 or check our indoor air quality service page.