Does a mini-split need a MERV 13 filter? Two Title 24 codes disagree

You're specifying a ductless mini-split for a nonresidential tenant improvement. The CALGreen checklist comes back with a correction: install MERV 13 filtration. Here's the problem — most ductless mini-splits can't take a MERV 13 filter. They don't have the fan power to push air through it, and the head won't accept the thicker media. So which wins: the physics, or the checklist?

Right now the honest answer is that it depends on how your reviewer reads two sections of Title 24 that don't quite line up.

Two codes, one requirement, two scopes

Nonresidential CALGreen puts the MERV 13 rule in Section 5.504.5 Filters. The operative sentence is broad.

Verified against the 2025 CALGreen (Part 11) code text, §5.504.5: "In mechanically ventilated buildings, provide regularly occupied areas of the building with air filtration media for outside and return air that provides at least a Minimum Efficiency Reporting Value (MERV) of 13." Its only exception is "Existing mechanical equipment."

Read literally, that catches any mechanically ventilated building. It doesn't say how the air moves — no duct-length trigger, no equipment-type carve-out beyond existing equipment.

Now the Energy Code. Part 6, Section 120.1(c)1 carries the matching air-filtration rule, and it is narrower. It names the exact system types it applies to. The first one:

Verified against the 2025 California Energy Code (Part 6) code text, §120.1(c)1A(i): "Mechanical space-conditioning systems that supply air to an occupiable space through ductwork exceeding 10 ft (3 m) in length." Section 120.1(c)1B then sets the efficiency: "The filters shall have a designated efficiency equal to or greater than MERV 13…"

That's the whole difference in one clause. The Energy Code scopes MERV 13 to systems that push air through more than 10 feet of duct. A typical ductless mini-split — a wall or ceiling head blowing straight into the room, no ductwork — sits outside that scope. CALGreen's words don't draw that line.

Where it bites

Here's the thing: this isn't hypothetical. The Building Standards Commission's own materials for the September 1, 2026 CALGreen workshop say HVAC manufacturers and mechanical engineers have reported that some AHJs are applying the CALGreen MERV 13 requirement to ductless mini-split systems — reading 5.504.5 exactly as it's written.

And that reading collides with the hardware. Per BSC's rationale, most ductless mini-splits do not function with a MERV 13 filter because they lack the fan power, and the unit cannot accept the thicker filter medium. There's no product that complies and no legal path that works.

The state has said what it meant

BSC's fix is on the table for the 2028 code. Workshop Item 3(d) reads, verbatim, "Amend MERV filter Section 5.504.5 Filters to align with Part 6 Energy Code." The draft express terms would fold the Part 6 qualifier — "space-conditioning systems that supply air to an occupiable space through ductwork exceeding 10 ft (3 m) in length" — into 5.504.5. BSC's stated intent is blunt: "It is not the intent of the CALGreen nonresidential code to exclude the installation of ductless mini-split systems." Staff also reports it coordinated with Energy Commission staff and got positive feedback on the alignment.

But read this guardrail carefully: it is a pre-cycle draft, not adopted code. It still has to clear the 45-day public comment period (July–October 2027) and Commission adoption (December 2027–January 2028). The 2028 California Building Standards Code doesn't take effect until January 1, 2029. The language can change. Nothing here rewrites the code on your desk today.

What to do on a job now

So you're caught between the current words and the hardware. Two things are true at once, and you should carry both to your reviewer:

• The current 5.504.5 has no 10-ft qualifier. An AHJ reading it broadly is not wrong on the text alone — the carve-out simply isn't in the sentence yet.
• The Energy Code's matching rule is narrower, and the state has said the exclusion was never intended. That's a real basis to ask a reviewer to read 5.504.5 in harmony with Part 6 for a ductless head.

Bring the Part 6 scope (§120.1(c)1A(i)) and BSC's stated intent to the plan check, in writing, as your argument. Then verify the call with your local jurisdiction — the AHJ interprets the adopted code, and until the amendment lands, the reading is theirs to make. If you get a favorable one, get it in the record.

This is another HVAC plan-check trap where the code text and the equipment don't agree — the same shape as the A2L refrigerant tables. Knowing exactly where the two sections diverge is what turns a stalled correction into a conversation.

What CrossBeam does with it

CrossBeam flags where two parts of Title 24 scope the same requirement differently, so a ductless mini-split doesn't draw a MERV 13 correction the code never meant to trigger. It hands you the exact sections — 5.504.5 and 120.1(c)1A(i) — and the state's stated intent, so you can make the case to a reviewer before the correction letter goes out.