HRV vs ERV for California Title 24 Compliance
Title 24 requires neither. The whole-dwelling fan can be exhaust, supply, balanced or central-fan-integrated. If you choose an HRV or ERV, it must show fan efficacy of 1.0 W/cfm or less, a MERV 13 supply filter and reachable cores, with supply and exhaust flows within 20 percent of each other.
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Both are optional, and they are treated alike
An HRV moves heat between outgoing and incoming air; an ERV moves moisture too. The Energy Code words them alike, as "systems with heat or energy recovery", so the choice rests on climate, humidity and cost. The manual calls them most practical in tightly sealed houses and notes that two fans use more electricity.
The 1.0 W/cfm check
Section 150.0(o)2C caps fan efficacy at 1.0 W/cfm, verified under RA3.7.4.4 from the HVI directory. The rater takes the power listed at 32 degrees F for the net airflow at or above the required airflow, then divides watts by cfm. If the certificate requires 60 cfm and the directory lists 45 watts at 62 net cfm, the result is 0.73 and passes.
What balanced earns
The ventilation equation gives a balanced system the full infiltration credit. Using the manual's Example 4-6 inputs (84 cfm total, 14 cfm infiltration, 25 percent shared wall), an exhaust fan must move 82 cfm and a balanced system about 73.5. Supply and exhaust must be within 20 percent, and their average must meet the requirement.
Installation rules that follow the choice
- The supply side takes a MERV 13 filter, which may sit downstream of the core if another filter protects it upstream.
- Filters and cores are reachable from occupiable space, a basement, garage, balcony or mechanical closet, behind a panel not over 10 feet above a walking surface. A unit serviced from the attic needs a fault indicator display, an attic door or hatch with ladder and a walkway.
- The intake is reachable, should sit away from barbecue and gas appliance exhaust, and may not draw from an attic or crawlspace.
- New homes prescriptively need a fault indicator display, and a performance model without one earns less credit.
In an existing house
Replacing a whole-dwelling fan meets the airflow rule only where an earlier permit required one. Sizing is on fan sizing, filters on MERV 13 sizing, and the background on whole-house ventilation, the IAQ fan and the ADU version. Start at residential.
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
Neither is favored by the Standards. Both face the same 1.0 W/cfm limit and filter rules, and the compliance software credits the heat recovery efficiency entered for the model.
Yes. The compliance manual works an example in which a bathroom exhaust fan meets the requirement, provided it is rated for the airflow and for 1.0 sone or less.
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View all Ventilation guides → · HVAC and Water Heating · Title 24 guide