Adding Air Conditioning to an Existing House: Title 24 Requirements
Adding cooling to an existing house is an alteration. A coil or outdoor unit on the existing furnace brings a duct test, a setback thermostat and, in zones 2 and 8 to 15, a charge check with 300 cfm per ton of airflow. A whole new ducted system must instead meet the rules for new systems.
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Five questions that fix the scope
- Is there a blower and duct system to reuse? A coil or condensing unit added to it triggers Sections 150.2(b)1E and 1F. New equipment plus duct at least 75 percent new material makes an entirely new system under Section 150.2(b)1C.
- Which climate zone? Charge and airflow checks reach an air conditioner only in zones 2 and 8 to 15. The thermostat and duct rules apply everywhere.
- Which airflow sets the duct pass number? If the ducts are tested before the cooling equipment is chosen, or its specification is unknown, Appendix RA3.1.4.2 uses a default of 0.5 cfm per square foot of floor. A 1,600 square foot house gives 800 cfm, so 10 percent is 80 cfm and 7 percent to outside is 56 cfm. Once a single-indoor-unit system is chosen, 400 cfm per ton applies: 2.5 tons gives 1,000 cfm, so 100 and 70.
- Can the existing return carry the air? Where charge is verified, an altered system must reach 300 cfm per ton, 750 cfm for 2.5 tons. The appendix notes that adding a return duct and filter grille, or enlarging the old one, often fixes a shortfall.
- Is anything in a garage? Ducts, coils or an air handler there need 6 percent leakage or a smoke test, whatever the length.
A trap when heating is replaced too
If the project replaces a ducted electric resistance furnace while installing central cooling, the new heat cannot be ducted electric resistance, except in zones 7 and 15 (the manual's Example 9-45). Baseboard heat that stays ductless is allowed when the existing heat is electric resistance.
Documents and next pages
The alteration goes on CF1R-ALT-02-E, with the installer's CF2R forms and the rater's CF3R forms for each test. The building department decides what it wants at the counter. The three installation routes are set out on adding central air, the thresholds on duct leakage testing, and the airflow test on airflow verification. A ductless option is the mini-split checklist, and reports 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
Yes. Section 150.2(b)1E names the installation of a cooling or heating coil. The test is skipped only for under 40 linear feet of duct, ducts already sealed and verified, or asbestos.
Not for adding cooling alone. The exception is electric resistance: a ducted electric furnace replaced alongside new ducted cooling must become a heat pump or gas, outside zones 7 and 15.
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