Does Title 24 Require a Whole House Fan?
Not as a mandatory measure. The prescriptive package requires one only for a new home, or an addition over 1,000 square feet, in climate zones 8 to 14, and the performance path lets you trade it for other measures. It is a cooling fan, a different appliance from the fresh-air ventilation system every new home must have.
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Where the requirement applies
Section 150.1(c)12 and Table 150.1-A mark the fan required in zones 8 to 14 and not required in zones 1 to 7, 15 and 16. Two exceptions apply: a new dwelling unit of 500 square feet or less, and an addition of 1,000 square feet or less. Section 150.2(b), the list of what an alteration must meet, does not name a whole-house fan, so nothing makes an existing house add one. Find your zone on the climate zone page.
How big it must be
The fans must together move at least 1.5 cfm for every square foot of conditioned floor area, using the airflow in the Home Ventilating Institute certified products directory. Where a fan is required, only listed models may be installed. A 2,000 square foot home therefore needs 3,000 cfm from one fan or several.
The attic vents
The fan pushes air into the attic, so the attic needs relief: at least 1 square foot of vent free area for each 750 cfm of rated airflow, or the manufacturer's figure if higher. Those 3,000 cfm call for 4 square feet. A fan vented directly outdoors is excepted. In a fire hazard zone the vents must also resist embers, and their mesh cuts net free area, as the wildfire rebuild guide explains.
What the owner receives
A house with a required fan must hand the owner a one-page sheet headed "How to operate your whole-house fan".
On the performance path
Using the performance approach, the software offers three choices, per the compliance manual.
- No fan assumed, with the cooling effect left out of the model.
- A default fan, derated to allow for undersized or inefficient installations.
- An ECC-verified fan, measured for airflow and efficacy under Residential Appendix RA3.9 and credited without derating, including at a higher airflow or lower watt draw than the default.
A central fan ventilation cooling system, which sends outdoor air through the central ducts, can be chosen in place of a fan. An ECC-Rater verifies it.
Not the ventilation fan
The mandatory fresh-air fan under Section 150.0(o) is sized by a different formula, runs at a fraction of the airflow and cannot rely on open windows. See sizing the ventilation fan, whole-house ventilation and the new home report.
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
No. The alterations list in Section 150.2(b) names no whole-house fan. The requirement reaches new homes and additions over 1,000 square feet in zones 8 to 14 on the prescriptive path.
Yes, by using the performance approach and making up the difference with other measures. The prescriptive package requires it.
When the fan is required, only models listed in the Home Ventilating Institute certified products directory may be installed, and their listed airflow is used for sizing.
Explore Ventilation
- Whole-House Ventilation Fan Sizing Under Title 24
- Whole-House Ventilation Requirements
- Title 24 Bathroom Exhaust Fan Requirements
- Can Bathroom Exhaust Fans Serve as Whole-House Ventilation?
- Can Existing HVAC Serve a New Home Addition?
View all Ventilation guides → · HVAC and Water Heating · Title 24 guide