Can My Furnace Fan Provide Whole-House Ventilation? CFI Under Title 24
Yes, as a central fan integrated (CFI) system, but not simply by running the furnace fan. It needs a motorized outdoor-air damper, controls that track run time, certification to the Energy Commission, and an air handler within the fan efficacy limit. An ECC-Rater verifies both the total airflow and the outdoor airflow.
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Start with the arithmetic
Suppose a house needs 100 CFM of ventilation. If the duct mixes in 10 percent outdoor air and the controls limit the fan to 30 minutes of every hour, outside air must arrive at 200 CFM while the fan runs, so the air handler must deliver 2,000 CFM (manual Example 4-9). Add a 50 CFM exhaust fan running all the time and a 1,000 CFM furnace is enough (Example 4-10).
The four control rules
- Continuous operation of the air handler is not an allowed way to ventilate (Section 150.0(o)1Bi).
- A motorized damper on the outdoor-air duct must stop all airflow into or out of the duct system when closed (1Bii).
- The damper opens only when ventilation is needed and closes whenever the air handler is off; a fan-powered outdoor-air supply stays off when the damper is closed (1Biii).
- Controls track outdoor-air run time and open or close the damper accordingly. When the thermostat is not calling, they run the central fan as needed to meet the requirement (1Biv). Averaging is limited to three hours.
Certification and fan efficacy
The manual says CFI systems count as intermittent systems and must be certified to the Energy Commission as capable of meeting Section 150.0(o); the Commission posts a listing. For new construction the prescriptive list caps the air handler at 0.45 W/cfm for a gas furnace and 0.58 W/cfm for other units, or 0.62 for small duct high velocity (Section 150.1(c)10), verified under RA3.3.
Filters and leakage testing
Outside air must pass a MERV 13 filter upstream of the coil: the air handler's inlet rack can serve, or filters go at the return grilles plus another in the outdoor-air duct. In a duct leakage test the outdoor-air duct is not taped off, but its damper can be closed.
What the rater measures
The ECC-Rater checks both the whole-system airflow and the much smaller outdoor ventilation airflow. The ventilation fan page has the Qfan formula; compare MERV 13 sizing, HRV versus ERV and whole-house ventilation. The residential page covers 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
No. Continuous operation of the central air handler is not a permissible method of providing the whole-dwelling ventilation airflow.
The outdoor-air ductwork is part of the leakage test and may not be taped off, though the required motorized damper can be closed for the test.
Explore Ventilation
- Do I Need a Ventilation Fan if I Can Open My Windows? Title 24
- Fresh-Air Intake and Supply-Only Ventilation: Filter and Access Rules
- HRV vs ERV for California Title 24 Compliance
- How Many CFM Does the Ventilation Fan Need?
- MERV 13 Filter Sizing for Title 24
View all Ventilation guides → · HVAC and Water Heating · Title 24 guide