DOAS + Water-Loop Heat Pump: A New Prescriptive Path Under 140.4(a)3

The change at the counter

Here's the thing: a design team that wanted to run a dedicated outdoor air system (DOAS) paired with a water-loop heat pump (WLHP) on an office or school building used to have exactly one way to get it approved — the performance method. Model the building, prove the energy budget, carry the paperwork. The prescriptive path in Section 140.4(a)3 of the 2025 Energy Code didn't list that system, so you couldn't use it.

That changed on March 18, 2026. The Energy Commission's Executive Director issued a determination that a DOAS+WLHP system "may be used to satisfy the prescriptive requirement for multi-zone space conditioning systems specified in Section 140.4(a)3." No code amendment, no new edition of the book — one signed memorandum, and a new prescriptive option exists.

Why a memo can do this

Section 140.4(a)3 sets prescriptive multi-zone HVAC requirements for office buildings and school buildings. It lists four qualifying system types: a VRF heat-pump system with a DOAS, four-pipe fan coils with a DOAS and an air-to-water heat-pump (AWHP) hot-water loop, a VAV system on an AWHP loop, and a dual-fan dual-duct (DFDD) system.

Then comes the clause that matters. Item 140.4(a)3Av allows:

"A space-conditioning system determined by the Executive Director to use no more energy than the systems specified in Section 140.4(a)3."

Verified against the 2025 Energy Code corpus: §140.4(a)3A lists options i–iv, and item v delegates the call to the Executive Director. That delegation is the whole mechanism.

So the code itself built the door. The Statewide CASE Team submitted DOAS+WLHP in January 2026; a public comment period ran from February 3 through March 4 with no comments received; staff confirmed the system "use[s] no more energy than the systems specified in Section 140.4(a)3"; and on March 18 the Executive Director signed. The result is a prescriptive-equivalent system without touching a word of Part 6.

What actually qualifies

This is the part to put on the mechanical sheets. The determination isn't a blank check for any DOAS-plus-heat-pump scheme — it approves a specific configuration spelled out in the memo's Attachment 1. To ride the prescriptive path, the system must meet all of these:

• It must be a WLHP system, with the common loop using cooling towers for heat rejection and AWHPs for heat addition — and AWHPs may not be used for heat rejection.
• Supplemental heating comes from either an electric boiler sized at no more than 50% of the heat-pump loop's design heating capacity or airside electric resistance heat complying with Exception 2 to Section 140.4(g) — not both.
• Indoor fans meet Section 140.4(a)3D.
• Ventilation to every zone is delivered by a DOAS complying with Section 140.4(a)3E.

Miss one of those and you're back to the performance method.

Check scope before you lean on it

One more gate, and it's easy to trip. Section 140.4(a)3 is a prescriptive requirement for a bounded set of buildings. Exception 1 to Section 140.4(a)3 removes buildings greater than 150,000 square feet or greater than five habitable stories, and Exception 2 removes school buildings in Climate Zones 6 and 7. If your project falls under an exception, the whole prescriptive section — determination included — doesn't apply, and you're doing performance compliance anyway.

Worth a note for the terminology-minded: "WLHP" isn't a new coinage here. It already appears in the 2025 code at Section 140.4(k)7, "Hydronic heat pump (WLHP) controls," which sets the common-loop dead-band controls a compliant system needs regardless.

What to write on the plans

Concrete version: if you're taking the prescriptive path with DOAS+WLHP, cite the determination as the compliance basis. It's docketed under 26-BSTD-01 as TN 269244, dated March 18, 2026, and signed by the Executive Director. Put that reference on the mechanical compliance sheet next to your 140.4(a)3 call-out, and mirror each of the Attachment 1 conditions in the equipment schedule and sequences so a reviewer can tick them off without hunting.

And because a plan checker at the counter may not have seen the memo yet, bring a copy. It isn't in any printed code book, and it won't be until a future code cycle folds it in. Confirm acceptance with your local jurisdiction before you commit the design — a determination is statewide, but the reviewer still has to recognize it.

What CrossBeam does with it

CrossBeam tracks determinations like this one alongside the published code, so a DOAS+WLHP project gets checked against the prescriptive option that actually exists today — not just the four options in effect since January 1. It surfaces the Attachment 1 conditions and the 140.4(a)3 scope exceptions up front, so the compliance path is confirmed before the sheets ever reach the counter.