HVAC sizing per ACCA Manual J (loads), Manual S (equipment), Manual D (ducts); duct leakage ≤ 4-8 cfm/100 sqft

Description

ENERGY STAR-certified homes require HVAC equipment sized per ACCA Manual J (room-by-room load calculation, NOT rule-of-thumb sqft/ton), equipment selected per Manual S, and ducts sized + designed per Manual D. Duct leakage to outside must be ≤ 4 cfm per 100 sqft of conditioned floor area (or ≤ 8 cfm/100 sqft total). All ducts installed in unconditioned space must be sealed + insulated. A National HVAC Design Report must be on file.

Why this exists

Oversized HVAC is the most common waste in residential — typical contractors size systems 1.5-2× larger than the home actually needs, causing short-cycling, poor humidity control, and higher cost. Architects should require Manual J load calcs on the project from day one and not let the HVAC contractor go off rule of thumb.

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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

• Slab-on-grade vapor barrier + capillary break required · HUD RSDG §4.6
• Roof overhangs protect walls — 12-24 inches in humid climates; one foot per story below · HUD RSDG §5.6.5
• ENERGY STAR certification: HERS-index target + Rater field checklist + HVAC quality install · ENERGY STAR SFNH §Overview — Certification path
• Grade I insulation installation: no gaps, no compression, fully filling cavity, supported aligned with air barrier · ENERGY STAR SFNH §Rater Field Checklist — Section 1 (Insulation + Air Barrier)
• Continuous air barrier on all six sides of conditioned space — including rim joists, knee walls, attic floor · ENERGY STAR SFNH §Air Barrier — continuous on all six sides of every conditioned space