What is a mechanical plan for an ADU and what does it show?

A mechanical plan for an ADU is the permit-ready drawing set that documents the complete HVAC and ventilation design — the equipment, its sizing math, where every component goes, and how the air moves. It gives the plan reviewer everything needed to confirm the system is safe, correctly sized, and code-compliant, and it coordinates cleanly with your Title 24 report.

What the drawing set contains

A typical ADU mechanical set runs one or two sheets (M-1, M-2) and includes:

• Mechanical floor plan showing the indoor equipment, supply/return points, exhaust fans, and the outdoor condenser location with required property-line and window setbacks.
• Equipment schedule — a table listing each unit's manufacturer, model number, capacity in BTU/hr, and efficiency ratings (SEER2/HSPF2 for heat pumps), so the reviewer can verify Title 24 minimums.
• Heat-load (Manual J) summary establishing the peak heating and cooling loads the equipment is sized to.
• Mini-split head and condenser layout with refrigerant line-set routing drawn from each indoor head to the outdoor unit.
• Duct layout where a ducted system is used, including register locations and duct sizing.
• Ventilation design per ASHRAE 62.2 — the whole-building mechanical ventilation rate and equipment, plus local exhaust (bath fans, kitchen hood ducted to the exterior).
• Condensate drainage routing for the indoor units.
• General notes and a title block citing the applicable codes (CMC, CBC, Title 24) and identifying the project.

What the plan proves to the reviewer

Plan check is really verifying two things: that the system is safe and correctly sized, and that it matches the energy-compliance documents. The Manual J summary and equipment schedule together prove sizing and efficiency; the ventilation design, ducted exhaust, and condenser placement prove the design meets the California Mechanical Code and won't create a nuisance for neighbors. A mechanical plan is sized to your ADU's square footage and climate zone, not pulled from a template — the load calculation drives the equipment selection.

What you receive — checklist

1. Mechanical floor plan with equipment locations and setbacks.
2. Equipment schedule (make, model, BTU/hr, efficiency).
3. Manual J load-calculation summary.
4. Line-set and/or duct routing.
5. ASHRAE 62.2 whole-building ventilation plus local exhaust.
6. Condensate, general notes, and title block.

Sheet counts, local amendments, and submittal requirements vary by jurisdiction — confirm with your local building department. Our mechanical plans start at $995 as a single discipline, scaled by ADU size, and you can pair them with electrical and plumbing in the size-scaled Full MEP package. See pricing or start your order.