Home Addition With a Mini-Split: Title 24 Design Guide
A ductless mini-split heat pump is an easy fit for an addition: no ducts to seal, no capacity maximum. It still needs a load calculation, must be a heat pump rather than electric resistance, and has its refrigerant charge verified with an ECC-Rater in every climate zone. That verification puts the project on a registered CF1R.
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What ductless skips
Duct sealing and duct insulation apply to extended ducts, and a ductless system has none. Ductless systems are also excepted from the maximum capacity limits of Section 150.2(a)1E. In zones 4 and 8 to 16, mandatory roof deck insulation for new attics over conditioned space has an exception for ductless systems (Section 150.0(a)1).
What it must still pass
- Heat pump type. Table 150.1-A calls for a heat pump. Electric baseboard in place of it is reachable only through performance (Example 9-37).
- Load calculation. Section 150.2(a)1E applies, with infiltration limited to Table 150.2-C unless tested. A heat pump has no maximum heating capacity, and its minimum is the building code's.
- Charge verification. A new system serving the addition meets new-home space-conditioning rules, including charge verification for heat pumps in all zones (Example 9-11), with measurement access holes unless the unit cannot take them.
When the standard test does not fit
Some mini-splits cannot be verified by the standard procedure. The installer then charges by the weigh-in method and the ECC-Rater verifies by watching it, which means the rater must be on site the day the system is charged. Book accordingly.
Placement choices
If the addition is a separate dwelling, ductless equipment avoids the shared-return ban and the unit needs its own thermostat. For the variable capacity heat pump credit, indoor units sit entirely in conditioned space, with wall-mounted thermostats in zones over 150 square feet and airflow to every habitable space.
If the space is already conditioned
A mini-split installed into existing conditioned space, such as a converted basement, is an alteration instead (Example 9-7b); see adding central air.
Related: refrigerant charge verification, heat pump requirements, existing HVAC and the residential service.
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
Not when no ducts are involved. Duct sealing applies to ducts that are extended or replaced; the verification needed is the refrigerant charge check.
Not prescriptively. Electric resistance heat for a new addition is reachable only through performance compliance, where other features must make up the energy use.
Explore Mini-Splits
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- 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
- Refrigerant Line Set Insulation on an AC or Mini-Split: What the Code Requires
View all Mini-Splits guides → · HVAC and Water Heating · Title 24 guide