Fresh-Air Intake and Supply-Only Ventilation: Filter and Access Rules
A supply-only or makeup-air system that brings outside air indoors needs a MERV 13 filter that the owner can reach, labeled with its design airflow and clean-filter pressure drop. Intakes must be accessible, normally within 10 feet of a walking surface, and the air must come from outdoors, not from a garage or attic.
- Choose your report
- Upload your plans
- Pay securely
- Permit-ready report by email
Rules in the order an installer meets them
- Filter required. Mechanical supply-only ventilation and makeup air systems that bring outside air to an occupiable space must have filters. So must the supply side of balanced, HRV and ERV systems (Section 150.0(m)12A).
- MERV 13 or better, or the particle-size alternative listed in the same section (12C).
- Filter sits ahead of conditioning parts. Outdoor air is filtered before passing any thermal conditioning component (12Bi). HRV and ERV units may filter downstream if an ancillary filter sits upstream.
- Owner access. The filter must be reachable for regular service by the owner (12Biii), with sealed gaps around the inserted filter (12Bv).
- Labeled. A permanent label at the filter location discloses the design airflow and the maximum clean-filter pressure drop (12Biv). For supply-only and balanced systems that drop is set by the system design (12Diii).
Where the filter and intake can be
Filters sit where they can be serviced from occupiable spaces, basements, garages, balconies or mechanical closets, behind panels or grilles not more than 10 feet above a walking surface (Section 150.0(o)1Civ). Outdoor air intakes follow California Mechanical Code Section 402.4.1, must be accessible for cleaning, and comply if no more than 10 feet above a walking surface; roof-mounted intakes follow CMC Section 304.3.1.
Equipment in the attic
If the filter or unit can only be serviced from inside the attic, the exception requires three things: a fault indicator display meeting Joint Appendix JA17, an attic access door in a wall or a ceiling hatch with an integrated ladder, and a walkway from the door to the unit. An intake serving equipment with that display is excused from the 10-foot rule.
Where the air may come from
The compliance manual states that ventilation air must come from outdoors and may not be transferred from adjacent dwellings, garages, unconditioned attics or crawl spaces.
Related pages
Compare MERV 13 sizing for ducted systems, balanced systems and the furnace-fan option. See also residential reports.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
The ECC-Rater verifies whole-dwelling airflow for the ventilation system on a CF3R. Ask the rater to confirm which items on your CF1R are verified.
No. The requirement is MERV 13 or better, or the particle-size efficiency alternative in Section 150.0(m)12C.
Explore Ventilation
- HRV vs ERV for California Title 24 Compliance
- How Many CFM Does the Ventilation Fan Need?
- MERV 13 Filter Sizing for Title 24
- Is Your Range Hood Title 24 Compliant?
- Does Title 24 Require a Whole House Fan?
View all Ventilation guides → · HVAC and Water Heating · Title 24 guide