How-To Guide

How to Read MEP Drawings

Understand mechanical, electrical, and plumbing drawings for better coordination

MEP drawings show the systems that make a building work: HVAC, electrical power and lighting, plumbing, and fire protection. These systems occupy the same spaces and require careful coordination. Here's how to read them.

Step 1: Know the Sheet Designations

MEP drawings are organized by discipline:

MMechanical (HVAC)
Ductwork, equipment, piping, controls
EElectrical
Power, lighting, low voltage, fire alarm
PPlumbing
Domestic water, sanitary, storm, gas
FPFire Protection
Sprinkler systems, standpipes, fire pumps

Step 2: Read Mechanical (HVAC) Drawings

Mechanical drawings show air distribution and temperature control:

Supply Ductwork
Usually shown with solid lines, labeled with size (24x12)
Return Ductwork
Often shown with dashed lines or different line weight
Diffusers/Grilles
Symbols at duct terminations with CFM values
Equipment
RTUs, AHUs, VAV boxes shown as rectangles with tags
Elevations
Duct centerline elevations shown as CL EL XX'-XX"

Step 3: Read Electrical Drawings

Electrical drawings are often split into multiple plan types:

Power Plans
Receptacles, equipment connections, panel locations
Lighting Plans
Light fixtures, switches, circuiting
Fire Alarm Plans
Detectors, pull stations, horns/strobes
Low Voltage Plans
Data, telecom, security, AV systems

Key information: Circuit numbers connect devices to panels. Panel schedules show circuit loads and breaker sizes.

Step 4: Read Plumbing Drawings

Plumbing drawings show water supply and drainage systems:

DCW
Domestic Cold Water
Often solid line
DHW
Domestic Hot Water
Often dashed line
SAN
Sanitary Waste
Heavy line, slope noted
SV
Sanitary Vent
Connected to waste, runs to roof
SD
Storm Drain
Roof drains and leaders

Step 5: Understand Pipe and Duct Sizing

Size callouts tell you what will fit in the available space:

Rectangular Duct: 24x12

24" width x 12" height

Add insulation thickness (typically 1-2") to get actual envelope

Round Duct: 14Ø

14" diameter

Ø symbol indicates diameter

Pipe: 4" or 4"Ø

Nominal pipe size (actual OD varies by material)

Add insulation for hot/cold water and chilled water pipes

Step 6: Find Equipment Schedules

Equipment is tagged on plans and detailed in schedules:

Air Handling Unit Schedule: Capacity, motor HP, coil sizes
VAV Box Schedule: CFM, heating capacity, controls
Pump Schedule: GPM, head, motor HP
Panel Schedule: Circuits, loads, breaker sizes
Fixture Schedule: Fixture types, connections, counts

Step 7: Check for Coordination Information

Look for information needed to coordinate with other trades:

Routing elevations (top, bottom, or centerline)
Penetration sizes through structure
Equipment weight for structural coordination
Electrical requirements for mechanical equipment
Drain connections for mechanical equipment

Related Guides

How to Read Structural Drawings
Understand columns, beams, and framing plans.
Electrical Plan Symbols Guide
40+ common electrical symbols explained.

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