California Title 24 indoor air quality requirements, explained.

If you've remodeled a kitchen, added a new HVAC system, or bought a home in California in the last decade, you've encountered Title 24 — usually as a confusing line item on your contractor's quote or a stack of compliance paperwork at closing.

Title 24 isn't optional. It's California state law, and it sets some of the strictest residential indoor air quality requirements in the country. This guide breaks down what Title 24 actually requires, why it matters for your indoor air quality, and what California homeowners need to know.

What is Title 24?

"Title 24" refers to Part 6 of the California Code of Regulations — the Building Energy Efficiency Standards. First adopted in 1978, it's updated every 3 years (most recently in 2022, with the 2025 update taking effect January 1, 2026).

The standard covers building energy efficiency comprehensively, but a major focus is indoor air quality, including:

• Mechanical ventilation requirements
• Air filtration minimum efficiency (MERV ratings)
• Duct sealing and leakage limits
• Kitchen and bathroom exhaust requirements
• Whole-house ventilation rate calculations

The 5 Title 24 requirements that affect California homeowners

1. Whole-house mechanical ventilation (ASHRAE 62.2)

California homes built or remodeled after 2008 must have mechanical ventilation — either an exhaust-only system, a balanced system (HRV/ERV), or supply-only. The minimum ventilation rate is calculated based on home size and occupancy.

For a typical 2,000 sq ft, 3-bedroom California home: approximately 75 cubic feet per minute of continuous mechanical ventilation.

2. Minimum MERV-13 filtration

The 2022 Title 24 update requires MERV-13 filters (or higher) for any HVAC system installed in new construction or major remodels. MERV-13 filters capture particles down to 0.3-1 micrometers — including wildfire smoke PM2.5, pollen, and pet dander.

If your home was built before 2022 and uses MERV-8 or lower filters, you're below current code. Upgrading to MERV-13 is one of the highest-ROI indoor air quality investments you can make.

3. Duct leakage limits (HERS verification)

Title 24 limits the maximum leakage from ductwork:

• New construction: ≤5% of total airflow
• Major retrofit: ≤10% (or ≤15% with mitigation)

Leakage is measured by a certified HERS rater using a duct blaster test. If you've ever had a "HERS test" performed during a remodel — that's what it was checking.

Why this matters for IAQ: Leaky ducts in attics or crawlspaces pull contaminated outdoor air, insulation fibers, rodent debris, and pollen into your home's HVAC system. Sealed ducts = cleaner indoor air.

4. Kitchen range hood exhaust

Kitchen range hoods must vent outside (not recirculate), at minimum 100 CFM for typical homes or 5 air changes per hour for the kitchen volume — whichever is greater. Re-circulating hoods are no longer compliant for any new install or major remodel.

5. Bathroom exhaust

Every bathroom must have a mechanical exhaust fan capable of 50 CFM intermittent or 20 CFM continuous, vented outside.

What this means for your air ducts

Title 24 essentially treats your duct system as part of the building envelope — it must be tight, sealed, and properly sized. This has 3 implications for indoor air quality:

• Sealed ducts run cleaner. No outside contaminants getting pulled in
• MERV-13 catches more. Wildfire smoke, mold spores, allergens
• Higher filter efficiency = more buildup on ducts. Counter-intuitively, more efficient filters mean MORE particulate accumulates near the filter and inside the air handler, requiring more frequent professional cleaning

When does Title 24 actually trigger?

Title 24 doesn't apply retroactively to existing homes — but it triggers any time you:

• Build new construction
• Replace or add an HVAC system
• Perform a "major" remodel (typically >50% of conditioned space)
• Add square footage
• Replace ductwork

If you live in an older California home and are not remodeling, you don't have to comply — but you may be living below modern indoor air quality standards.

How to upgrade an older home to modern IAQ standards

You don't need a full remodel to bring your indoor air quality up to Title 24 levels. The 4 highest-impact upgrades:

1. Upgrade to MERV-13 filters — confirm your system can handle the airflow restriction first
2. Have ducts professionally sealed with aerosol mastic ("Aeroseal") — closes leaks without opening walls
3. Add a whole-house mechanical ventilator (HRV or ERV) — improves IAQ while saving energy
4. Schedule professional air duct cleaning — remove decades of accumulated particulate before tightening the system

What about wildfire smoke?

The 2025 Title 24 update introduces specific requirements for wildfire-affected areas, including:

• Higher-rated filtration in designated wildfire zones
• Dedicated "smoke ready" mode requirements for HVAC systems
• Outdoor air intake closure capabilities during wildfire events

If you live in a wildfire-prone California area, the 2025 standards specifically address smoke infiltration during fire events.

Who verifies Title 24 compliance?

Title 24 compliance is documented and verified by independent third-party certified inspectors:

• HERS raters — Home Energy Rating System certified inspectors who perform duct blaster tests, refrigerant charge verification, and other measurements
• Building inspectors from your local jurisdiction (city or county)
• Third-party plan reviewers for compliance documentation

If you're remodeling or building, your contractor should provide CF-1R, CF-2R, and CF-3R compliance documents at the appropriate stages.

Bottom line for California homeowners

Title 24 is the reason California homes have measurably cleaner indoor air on average than homes in many other states. If you're remodeling, building, or just want to bring your existing home up to modern standards — work with contractors and service providers who know the code.