LDD-28 · Kitchen Makeup Air (MUA) Infrastructure Routing

Status: 🟢 LOCKED v1.0 — adopted 2026-05-16. Supersedes the boost-ERV makeup-air approach previously locked in LDD-05 and LDD-07.

Naming note: Peter labeled this draft "M-02" (mechanical-system family). Filed here as LDD-28 to keep one canonical numbering sequence; the M-02 label is preserved as an alias.

Decision history: A prior decision (2026-05-15 PM) had retired this MUA line in favor of a boost-capable ERV that served dual duty as kitchen makeup air. Reversed 2026-05-16 — Peter chose the dedicated MUA for: (a) the architectural value of the east-facade flush charcoal louver + under-stair displacement register, (b) better tempering control + pressure balance during Hurricane Mode, (c) a smaller standard residential ERV freed for IAQ-only duty (cleaner spec, better daily performance). Net budget impact: ~$6–14K over the prior boost-ERV approach. LDD-05 + LDD-07 have been updated to drop the boost-ERV spec.

Cross-references (Peter's labels mapped to this set)

Peter's draft used cross-ref labels that don't match the actual LDD numbering. Mapped here:

One-line intent

Dedicated tempered makeup air unit interlocked with the kitchen exhaust — intake at the east facade hidden in a charcoal flush louver, routed through an acoustically-lined partition wall to a wall-mounted unit in the mechanical room, then under-slab south to an invisible under-stair floor register that diffuses tempered air into the space with zero visible utility.

Why this matters

The kitchen exhaust (LDD-07) runs well above 400 CFM in "Hurricane Mode," which triggers IMC makeup air requirements and threatens to depressurize the tightly-sealed IMP envelope (LDD-11) — backdrafting flues, sucking weatherstripping, slamming doors, killing combustion appliances. The mechanical answer is some form of matched makeup air; the architectural answer is to make that mechanical answer invisible. Peter's routing — east facade louver hidden in trim, partition-wall chase, under-stair diffuser — does the second part beautifully. The first part is what the LDD-05/07 conflict above is really about: is the ERV-as-MUA solution code-compliant and operationally sufficient, or do we need this dedicated unit?

Locked decisions (per Peter, v3.0)

System mandate

• Dedicated variable-speed tempered MUA unit, electronically interlocked low-voltage to the kitchen exhaust blower
• Ramps proportionally with exhaust CFM
• Maintains neutral pressure balance in the IMP envelope

East-facade intake

• 12"–14" round galvanized duct
• Horizontal penetration through east IMP wall
• Centerline at 11'0" AFF (above human sightline, above splash zone)
• Shifted as far north along the east wall as PEMB framing permits — protects the foyer entrance visual clarity
• Architectural flush louver, heavy-gauge, factory powder-coated to match the dark charcoal trim/window frame tone
• Integrates with the high horizontal trim geometry of the facade

Horizontal wall chase

• Routes westward inside the partition wall between cooking counter zone and breakfast nook / powder room
• Partition framed as minimum 2×6 or double-stud utility wall to house the duct
• Duct tightly wrapped in high-density insulation or specialized acoustic lagging before drywall enclosure — no "wind rush" audible in the nook during Hurricane Mode

Vertical drop into mechanical room

• Smooth long-radius 90° elbow at the wall threshold of the 7'×10' central mechanical room (LDD-15)
• Vertical drop down the inside face of the mech room wall, into the top intake collar of the MUA unit

MUA equipment

• Wall-mounted on the south wall of the mechanical room (mudroom wall axis)
• Cabinet contains: intake fan blower, motorized dampers, high-efficiency filtration
• Mounting strategy isolates fan harmonics + mechanical vibration inside the dedicated service room behind an insulated service door

Hydronic tempering

• Integrated hydronic heating coil piped into the primary radiant boiler loop (LDD-02)
• Pre-heats incoming sub-freezing winter air to a stable 60°F–65°F
• Prevents thermal shock + draft discomfort in the living zones

Under-slab discharge routing

• Tempered supply exits the bottom of the MUA, dives vertically through the slab inside the mech room envelope
• Below slab: heavy-wall PVC or coated spiral pipe routed south, beneath mudroom wall + foyer footprint
• Sits in the crushed-stone base below the structural slab
• Must be kept completely separate from any radiant PEX loops (LDD-02 coordination is critical)

Under-stair discharge

• Under-slab line surfaces beneath the southern structural stair (LDD-19)
• Terminates at a flush-mounted linear floor register tucked inside the open dead space beneath the stairs
• Stair underside acts as a natural baffle — breaks velocity, muffles air movement noise
• Air pools invisibly in the low-traffic southern zone, gently overflows into living + cooking spaces
• 100% draft-free, zero visible floor utilities

Routing diagram (Peter's ASCII)

[Exterior East Louver at 11' AFF] ──> (Horizontal Wall Chase behind Nook/WC)
                                                      │
                                                      ▼ (Vertical Drop inside Mech Room)
                                         [MUA Unit on South Mech Wall]
                                                      │
                                                      ▼ (Slab Dive)
   [Floor Register Under Stairs] <── [Under-Slab PVC Duct Run Heading South]

Open items / requires engineer review

• Resolve the LDD-05 / LDD-07 / LDD-28 conflict (banner above) — this is the v1.0 blocker.
• IMC requirement verification. Peter states "dedicated tempered MUA is legally required for 400+ CFM per IMC." IMC §505/§506 requires makeup air for exhaust over 400 CFM but allows it from any source that maintains pressure balance — including ERV/HRV in boost mode. The ERV-boost solution in LDD-07 was designed to meet the same IMC requirement via a different mechanical path. Confirm with the mechanical engineer whether IMC actually requires dedicated MUA, or whether either solution satisfies the code.
• Under-slab PVC + radiant tubing sequencing. Peter calls this out himself — the MUA sleeve must be in the crushed-stone base before PEX is laid and before the slab is poured. Coordinate with LDD-02 radiant slab installer + concrete sub. Once PEX is in, a forgotten sleeve means saw-cutting.
• PVC duct condensation risk under-slab. Cold winter intake air inside the PVC, warmer crushed-stone base outside — the PVC exterior is below dew point and may condense moisture in the granular base. Insulated PVC? Vapor barrier? Confirm.
• Mech room space planning. LDD-15 is 7'×10' = 70 sf. A wall-mounted MUA cabinet (typically ~3'×4' + service clearance ~3' in front) eats meaningful floor area. Verify the room still accommodates the radiant manifold + boiler + ERV + water heater + electrical equipment already implied.
• Hydronic coil load on radiant boiler. Tempering 1,000–1,500 CFM of -10°F outdoor air to 65°F = ~75°F lift × CFM × 1.08 ≈ 80–125 kBTU/h at peak. Add that to radiant slab load. Confirm boiler is sized for both, or specify a dedicated tempering source.
• East-facade louver penetration in IMP. IMP penetrations are thermal bridges + air-sealing risks. The "flush-mounted architectural louver" needs an air-tight installation gasket + thermal break. Coordinate with LDD-11 envelope penetration details.
• Acoustic lagging material spec. "High-density insulation or specialized acoustic utility lagging" — pick: mineral wool wrap, mass-loaded vinyl, neoprene foam, or proprietary duct silencer. Different choices have different fire-rating + acoustic performance.
• Pre-heat target validation. 60–65°F is "comfort neutral" but aggressive on the boiler at peak. A 50–55°F target saves significant winter heating energy and the living-zone occupants likely won't notice a 5–10°F difference at the diffuser since the air mixes with room air before reaching breathing height. Trade-study with the mechanical engineer.
• Under-stair "dead space" must actually exist. Coordinate with LDD-19 doors + stairs — if the southern stair is closed-string with storage or a coat closet underneath, there's no diffuser cavity. Lock this into the stair design now.
• Floor register coordination with LDD-24 flooring. Flush-mounted linear register transition to the gym-adjacent or living-wing floor finish. Pick the register material + edge detail.

Cross-references

• ← LDD-01 PEMB structural — east-wall louver penetration through PEMB cladding + framing; partition-wall chase reinforced to 2×6/double-stud framing.
• ← LDD-02 radiant slab — under-slab PVC routing must NOT conflict with radiant PEX loops; sequencing critical.
• ← LDD-05 HVAC system — ERV downsized to standard residential ($3–5K) for IAQ-only duty now that MUA handles kitchen makeup air.
• ← LDD-07 cooking + island ventilation — kitchen exhaust interlocks with this MUA in Hurricane Mode (formerly proposed to interlock with ERV boost).
• → LDD-09 electrical — low-voltage interlock wiring between exhaust blower control and MUA fan ramp.
• → LDD-11 exterior envelope — IMP penetration detail at the east-facade louver; air-sealing + thermal break + charcoal color coordination.
• → LDD-15 mechanical room — equipment mounting + space planning + service clearance + acoustic isolation behind insulated service door.
• → LDD-18 interior materials — partition wall framing finish + the architectural louver charcoal tone matching trim/window frame palette.
• → LDD-19 doors + stairs — under-stair dead space must exist for the diffuser register; coordinate stair design.
• → LDD-24 flooring — flush linear floor register integration with floor finish.

Cost drivers

The MUA gross cost, with the offsetting savings from downsizing the ERV (no longer needs boost-capable spec):

The LDD-05/07 boost-ERV approach already costs ~$5–10K extra for the higher-spec ERV. So the net incremental cost of adopting LDD-28 over the boost-ERV solution is:

LDD-28 (~$11–24K) − boost-ERV premium (~$5–10K already in budget) = ~$6–14K net add

This is consistent with LDD-07's "saves $8–12K by eliminating MUA" claim — the conflict is real, and the dollars are real.

Air-gap concerns

1. The LDD-05/07/28 conflict is the air-gap concern that matters most. Resolve before any of these systems go to bid. Surface this to the mechanical engineer at the next meeting.
2. IMC code interpretation. Confirm that the boost-ERV approach actually satisfies IMC §505/§506. If it does, the cost case for LDD-28 weakens; if it doesn't, the cost case for LDD-28 becomes a code requirement.
3. Under-slab PVC sleeve sequencing is unforgiving. This MUST go in before the slab pour. Add to the docs/todo.md pre-pour checklist alongside the radiant tubing photo/map/pressure-test item.
4. The under-stair diffuser is the cleverest part of this LDD, but it depends entirely on the stair design. Stair under-space must remain open. Lock this into LDD-19 before any stair fabrication.
5. Hydronic coil load on the radiant boiler is significant. 80–125 kBTU/h at peak is not trivial — verify boiler sizing accounts for radiant + MUA tempering simultaneous load. Better to learn this from the energy model than from a cold January morning.
6. East-facade louver air-sealing in IMP. IMP joints are the project's biggest air-seal story. A 12–14" penetration with a louver = a known thermal bridge + an air-leak risk. Detail with the IMP manufacturer.
7. PVC duct condensation under-slab. Verify the PVC spec handles cold-air condensation against warm crushed stone, or insulate the under-slab PVC.
8. Pre-heat target 60–65°F is energy-intensive. Trade-study against 50–55°F target — likely saves significant winter operating cost without occupant complaint.
9. Acoustic lagging fire rating. Mass-loaded vinyl is not Class A; mineral wool wrap is. Pick the material with the kitchen's fire-class environment in mind.
10. Filtration spec not stated. "High-efficiency filtration media" — what MERV? Kitchen MUA into a tight envelope deserves MERV 11–13 minimum; MERV 16+ if HEPA is desired. Lock this into the MUA cabinet selection.
11. Service access for filter changes. The wall-mounted MUA on the south mech room wall must allow filter access without removing other equipment. Confirm in the space-planning pass.

Diagram

Peter's ASCII routing diagram above is the canonical layout intent. A future Codex prompt should illustrate:

• (a) Plan view showing the east-facade louver, horizontal wall chase, mech-room vertical drop, MUA unit position, slab dive, under-slab south run, under-stair register
• (b) Section through the east facade showing the 11' AFF louver integration with charcoal trim line
• (c) Section through the mech room showing the MUA equipment + service clearance + hydronic piping integration

Status

🟢 Green — LOCKED v1.0 (adopted 2026-05-16). Highest-priority follow-ups before bidding: (1) verify IMC §505/§506 interpretation with mechanical engineer — either solution satisfies the code in our reading, but get it confirmed in writing; (2) coordinate under-slab PVC sleeve sequencing with LDD-02 radiant slab pre-pour checklist (added to todo.md); (3) confirm LDD-15 mechanical room space planning accommodates the wall-mounted MUA cabinet alongside existing radiant + boiler + ERV + electrical equipment.