Cooling-Only Mini-Split or Heat Pump Mini-Split: What Triggers More?
Under the alteration rules for an existing home, a heat pump mini-split needs field charge verification in every climate zone, while a cooling-only air conditioner mini-split needs it only in zones 2 and 8 through 15. The heat pump also brings defrost and backup-heat controls that the cooling-only unit never has.
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One sentence in Section 150.2(b)1Fii
When refrigerant-containing parts are installed or replaced in an existing home, air-cooled air conditioners in Climate Zones 2 and 8 through 15 and air-source heat pumps in all zones must have charge and airflow verified. The sentence names minisplit systems among the covered types, so the equipment type, not the brand or the number of heads, decides.
- Cooling-only unit: field charge verification in zones 2 and 8 to 15. None in zones 1, 3, 4, 5, 6, 7 and 16.
- Heat pump unit: field charge verification in all 16 zones.
A new head in an addition follows a different list, the charge entries on the CF1R, which come from Table 150.1-A.
How the test runs on either model
Most mini-splits cannot take the standard superheat or subcooling test, so Section 150.2(b)1Fiii sends them to the weigh-in route. The installer weighs in the charge and the ECC-Rater verifies it. A heat pump is tested in cooling mode only, since the standard method depends on outdoor temperature. Below 55 degrees F the rater may observe the weigh-in, and the thermostat must then conform to Section 110.12.
Controls only the heat pump has
- An installer-adjustable defrost delay timer must be set to 90 minutes or more, with exceptions for dwellings in zones 6 and 7, plus homes of 500 square feet or less in zones 3, 5 through 10 and 15 (Section 150.0(h)6).
- If backup heat is present, supplementary heat must lock out above 35 degrees F (Section 150.0(h)7). A mini-split with no backup heater skips this rule.
Shared rules
Both models replace thermostats with setback controls (Section 150.2(b)1Fi). If the unit replaces electric resistance heating, a heat pump is always an allowed replacement (Section 150.2(b)1G).
Which choice fits
For a new room, compare the addition design guide and the ADU mini-split page. The charge verification page explains the test, the installation checklist lists the paperwork, and residential reports start there.
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
In an existing home, the alteration rule does not require field charge verification for an air conditioner in zone 3. Thermostat and other mandatory rules still apply, and the building department confirms the scope.
No. The equipment type and climate zone decide. More heads add piping and charge adjustments but not a different rule.
Explore Mini-Splits
- Home Addition With a Mini-Split: Title 24 Design Guide
- How Many Heads Can a Mini-Split Have, and Does Adding One Trigger Title 24?
- Installing a Mini-Split Yourself: What Title 24 Still Requires
- Mini-Split in a Garage, Shed or Workshop: Does It Trigger Title 24?
- Mini-Split Installation Title 24 Checklist
View all Mini-Splits guides → · HVAC and Water Heating · Title 24 guide