# LDD-06 · Living Wing HVAC Distribution

> **Status:** 🟢 LOCKED v1.0 — supersedes prior diffuser/distribution summaries.

## One-line intent

Keep the trunk pure, the branches clean, and the air invisible.

## Why this matters

This is the LDD set's clearest example of "the system is the architecture." Treating diffusers as ceiling-composition elements rather than vents is a discipline that, if held, makes the living wing read as calm and intentional. If broken, the ceiling becomes the usual residential chaos.

## Locked decisions

**Primary organization**

- One N–S main trunk
- Five E–W primary branches
- One short local service branch from mech room serving foyer / WC / stair base

**Main trunk**

- ~14" round, pre-insulated
- Visually centered within living wing
- ~12' from spine wall
- Long-radius elbows only
- Sized for full build-out, not Phase 1 only
- Terminates cleanly within living wing — **does not continue into foyer or upstairs**

**Branches (5 total, E–W only, perpendicular to trunk)**

| # | Zone | Notes |
|---|---|---|
| 1 | Entry / stair / mech | May be partly supplemented by local south service branch |
| 2 | Kitchen work zone | Standing area, no direct down-blow |
| 3 | Kitchen + breakfast | Priority zone, strong but low-velocity mixing |
| 4 | Living / TV | No direct airflow on seating |
| 5 | North / Murphy / bath | Quiet retreat conditioning |

**Branch takeoffs**

- Smooth wye or angled, never hard 90° tap
- E–W only after takeoff (no diagonals)
- Balanced airflow across all branches

**Local south service branch**

- Short, direct, from mech room
- Serves foyer, stair base, adjacent WC
- May not behave as second trunk or compete visually with main trunk

**Stair + landing conditioning**

- Stair base: subtle indirect from local branch only
- Upstairs landing: part of upstairs HVAC zone
- No aggressive supply aimed up/down stair path

**Return air**

- Central return aligned with trunk
- Located away from supply diffusers
- High return preferred (ceiling or upper wall)
- Clear air path from all zones; no dead zones

**Diffusers**

- **Linear slot diffusers** (the preferred type)
- 8–10 outlets total, continuous runs where possible
- No diffuser directly over seating, table, cooking position, entry path, or stair
- Aligned with structural bays, ceiling geometry, lighting composition, circulation logic

**WC conditioning**

- Exhaust-driven primary
- Minimal indirect supply allowed
- No strong directional airflow

**Cooktop hood coordination**

- Hood duct runs east from cooktop
- Wide capture, narrows downstream
- Smooth curved transitions
- Fan near east exterior wall
- Does not interfere with main N–S HVAC trunk

## Open items / requires engineer review

- Final trunk diameter — 14" is a planning size; actual depends on tonnage. Could be 12" or 16".
- CFM per branch (Manual D)
- Diffuser count/length per branch
- Return air sizing and grille placement
- Make-up air interlock with the kitchen island exhaust system

## Cross-references

- ← [LDD-05 HVAC overview](05-hvac-system.md) — overall system strategy.
- ← [LDD-12 exposed ceilings](12-exposed-ceilings.md) — trunk is layer 2 of the hierarchy.
- ← [LDD-08 lighting](08-lighting-framework.md) — diffusers must support, not compete with, lighting layer.
- → [LDD-07 cooking ventilation](07-cooking-ventilation.md) — cooktop hood routing east; not through the main trunk.

## Cost drivers

This LDD is execution detail of [LDD-05](05-hvac-system.md). Incremental cost above LDD-05's $30–55K living-wing ducted budget:

- **Linear slot diffusers** vs standard round registers: $400–700 per linear foot installed. ~30–50 lf total ≈ $12–35K — a meaningful premium for the aesthetic.
- **Smooth wye takeoffs** + long-radius elbows: ~$2–5K premium over standard sheet metal fittings.
- **Central return well-located**: usually negligible incremental cost vs convenience-placed return.

**Likely-case incremental: $15–40K above generic ducted install. Reflected in LDD-05 rollup.**

## Air-gap concerns

1. **Linear slot diffusers are expensive to balance.** They look great when running but require careful damper setting + sometimes-volume control at each slot. Budget a commissioning visit by the HVAC contractor after move-in, ideally with a smoke pen and anemometer.
2. **Trunk at 12' from spine wall puts it dead-center over the living wing.** Visually that's the point — but check that this position doesn't conflict with the LDD-08 lighting linear runs, which may want the same centerline. Either the lighting offsets, or the trunk does.
3. **5 branches across 60' N–S = a branch every 12'.** That's denser than typical residential and means each branch handles a smallish CFM. Good for control granularity, but increases install labor and balancing complexity. Verify it's not over-engineered.
4. **Foyer conditioning via "subtle local branch" risks being either inadequate or never finished.** Be specific about the diffuser type, location, and CFM target there. The foyer is the first impression and is exterior-door-adjacent — it can be drafty without careful detailing.
5. **Cooktop exhaust running east through the ceiling could intersect the main trunk at the trunk centerline.** A vertical rise of the cooktop duct over the island might also intersect lighting linear runs. Coordinate before sheet metal fabrication.

## Diagram

![Living wing HVAC trunk with five branches](../../diagrams/09-living-hvac-trunk.svg)

## Status

🟢 **Green — distribution logic is clean.** Resolve diffuser balancing strategy with HVAC contractor; verify trunk vs lighting centerline conflict.