8 Things to Check on Every Mechanical Drawing Before You Stamp

Mechanical plan review is one of the most code-dense disciplines in construction. A single HVAC drawing set might need to comply with the IMC, ASHRAE 90.1, ASHRAE 62.1, ASHRAE 55, NFPA 90A/90B, and the local energy code, all at the same time. Here's a working checklist organized by the areas where issues appear most frequently.

1. Equipment schedules

Schedule completeness is the most common source of review comments in mechanical drawings. The schedule is where the design intent meets the spec, and gaps here propagate into every downstream coordination issue.

Field	Required	Common Issue
Design airflow (CFM)	All units	Listed for AHUs, missing for FCUs
Entering/leaving temps	All cooling units	Leaving temp omitted
Cooling capacity	All cooling units	Total shown, sensible missing
Heating capacity	All heating units	Usually present
Motor HP / electrical	All units	MCA/MOCP often missing
Minimum outside air	All ventilation units	Missing or inconsistent with 62.1 calc
Efficiency (IEER/SEER/COP)	All units per 90.1	Most commonly missing field
Sound ratings	Where specified	Often deferred to submittals

Most missed field

Efficiency data is the single most common schedule deficiency. If the schedule says "5-ton rooftop unit" but doesn't show the IEER, a code reviewer can't verify ASHRAE 90.1 energy code compliance from the drawings alone.

2. Ventilation rates (ASHRAE 62.1)

ASHRAE 62.1 ventilation rate compliance requires two things: correct outdoor air calculations and documentation that shows the work. The ventilation rate procedure (Section 6.2) calculates outdoor air based on people (Rp) and area (Ra) components for each zone, then adjusts for system-level efficiency.

Common errors include using occupant density from Table 6.2.2.1 without adjusting for actual anticipated occupancy, forgetting the area-based (Ra) component entirely, and calculating zone-level outdoor air correctly but not performing the system-level calculation for multi-zone systems (Section 6.2.5).

3. Equipment access clearances

IMC Section 306.5 (and manufacturer requirements, which are typically more restrictive) mandate minimum clearances around equipment for service access.

Beyond the code minimum

A 36-inch clearance on the service side is the IMC minimum, but many manufacturers require 48 inches or more for coil pull. The drawing may show adequate clearance for the code but not for the actual equipment being specified.

4. Duct sizing and pressure

Duct sizing isn't explicitly prescribed by the IMC, but ASHRAE 90.1 Section 6.5.3 sets maximum fan power limits that indirectly constrain duct sizing. Undersized ducts mean higher static pressure, which means more fan power.

Also verify duct material and construction class. SMACNA construction standards define pressure class and sealing requirements based on static pressure. A 4-inch WG duct system with Class C sealing (or no sealing class noted) will fail a leakage test and waste energy.

5. Refrigerant safety (ASHRAE 15)

Any system using more than a small quantity of refrigerant needs to comply with ASHRAE 15. The key checks: refrigerant quantity doesn't exceed the allowable limit for the occupied space, the mechanical room has the required refrigerant detection system, and ventilation of the mechanical room meets Section 8.11 requirements.

The industry shift to lower-GWP A2L refrigerants is triggering ASHRAE 15 requirements that designers haven't historically needed to address.

6. Energy code compliance (ASHRAE 90.1)

Beyond equipment efficiency, ASHRAE 90.1 has mechanical-specific requirements that are frequently missed: economizer requirements (Section 6.5.1), simultaneous heating and cooling limits (Section 6.5.2), energy recovery requirements (Section 6.5.6), and demand-controlled ventilation for high-occupancy spaces (Section 6.5.3.7).

DCV requirement

If a space has a design occupancy of more than 25 people per 1,000 SF, ASHRAE 90.1 requires demand-controlled ventilation. Conference rooms, training rooms, and dining areas frequently trigger this, and it's frequently absent from the control sequences.

7. Fire and smoke protection (NFPA 90A/90B)

Ductwork that passes through fire-rated assemblies needs fire dampers (for fire barriers) or smoke dampers (for smoke barriers), per NFPA 90A. Verify that damper locations are shown on the drawings wherever ducts penetrate rated walls and floor/ceiling assemblies. Also check that duct smoke detection required by Section 6.4.2 of the IMC is shown for systems over 2,000 CFM serving more than one floor.

8. Coordination with other disciplines

Mechanical drawings don't exist in isolation. Check for conflicts with structural elements (ducts routing through beams, equipment loads on non-structural roofs), electrical coordination (disconnect switches, VFD locations, conduit routing), and plumbing (condensate drainage, hydronic piping routing).

The most expensive miss

Does the structural engineer know about the rooftop equipment loads? A 6,000-pound air handler on a bar joist roof that wasn't designed for it is a problem that gets more expensive to fix the later it's discovered.

Using this checklist

This is a starting point, not an exhaustive list. Every project has jurisdiction-specific requirements, owner-specific standards, and design conditions that affect what to look for. The value of a checklist is that it catches the things that are easy to miss when you're focused on the hard stuff. In mechanical review, there's a lot of hard stuff to focus on.

Code references in this post are based on ASHRAE 90.1-2022, ASHRAE 62.1-2022, IMC 2024, and NFPA 90A 2024. Verify section numbers against your jurisdiction's adopted editions. Callout checks all of these simultaneously on every sheet. start with 50 free credits →