HVAC zoning: 1 zone per floor minimum; primary suite as its own zone in homes > 2500 sqft
ROT/EXT-HVAC-ZONING-BY-FLOORDescription
Multi-story homes benefit from at least one HVAC zone per floor — upstairs runs warmer than downstairs in summer, opposite in winter; separate zones let the system balance. Above 2500 sqft, the primary suite typically becomes its own zone for sleep-time setbacks. Open-plan single-story homes can sometimes work with one zone, but room temps vary significantly without careful diffuser design.
Why this exists
Single-zone whole-house systems create comfort complaints in every multi-story residential. The zone-per-floor rule is the architect's HVAC starting point — coordinate with the mechanical contractor on the equipment selection.
Categories
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Living spaces south-facing in cold climates · LIVING-SOUTH-FACING
- Mechanical room central, not corner · MECHANICAL-CENTRAL
- Water heater near fixtures · WATER-HEATER-NEAR-FIXTURES
- Roof orientation for future solar · SOLAR-ROOF-ORIENTATION
- Window-to-floor area: 12-20% for daylight quality; 8% is code minimum · ROT/EXT-WINDOW-AREA-TO-FLOOR
Last reviewed 2026-05-15.