mechanical-plumbing-systems

name	mechanical-plumbing-systems
description	HVAC and plumbing system installation, inspection, coordination, and commissioning for commercial construction.

Mechanical & Plumbing Systems Guide

Quick reference for construction project managers and field supervisors managing HVAC (Division 23) and plumbing (Division 22) trades on commercial and institutional projects.

Quick Reference Tables

HVAC Equipment Types

Equipment	Typical Application	Key Installation Concerns	Long-Lead Time
Air Handling Unit (AHU)	Large commercial spaces	Rigging access, vibration isolation, coil piping	12-20 weeks
Rooftop Unit (RTU)	Single-story retail/office	Roof structure, curb detail, crane access	8-16 weeks
Chiller (Air-Cooled)	Medium buildings	Pad/dunnage, electrical, clearances	16-24 weeks
Chiller (Water-Cooled)	Large buildings	Rigging, chilled/condenser water piping	20-30 weeks
Boiler (Hot Water)	Heating systems	Venting, gas piping, expansion tank	12-20 weeks
Cooling Tower	Water-cooled systems	Structural support, water treatment	14-22 weeks
VRF/VRV System	Multi-zone buildings	Refrigerant piping lengths, branch boxes	12-18 weeks
Fan Coil Unit	Hotels, apartments	Condensate drain, coordination	8-12 weeks

→ See hvac-equipment.md for detailed specifications and installation requirements.

Ductwork Pressure Classes & Sealing

Pressure Class	Static Pressure	Typical Application	Seal Class
0.5" WG	±0.5"	Low-velocity return	C (transverse only)
1" WG	±1"	Low-pressure supply	B (transverse + longitudinal)
2" WG	±2"	Medium-pressure supply	A (all seams + joints)
3" WG	±3"	High-pressure main ducts	A
4" WG	±4"	VAV systems	A
6" WG	±6"	High-velocity systems	A
10" WG	±10"	Industrial/exhaust	A

→ See ductwork-distribution.md for SMACNA standards and installation details.

Pipe Material Selection Guide

System	Common Materials	Joining Method	Max Temp
Chilled Water	Steel (Sch 40)	Welded, grooved	200°F
Hot Water <2"	Copper Type L	Soldered, press-fit	400°F
Hot Water >2"	Steel (Sch 40)	Welded, grooved	200°F
Steam	Steel (Sch 40/80)	Welded	366°F (150 psi)
Refrigerant	ACR Copper	Brazed	Per refrigerant
Domestic Cold	Copper Type L, CPVC, PEX	Various	180°F (copper)
Domestic Hot	Copper Type L, CPVC, PEX	Various	180°F
Sanitary Drain	Cast Iron, PVC DWV	Hub, no-hub, solvent	140°F (PVC)
Storm Drain	Cast Iron, PVC	Hub, no-hub, solvent	N/A

→ See piping-systems-hvac.md and plumbing-piping-water.md for complete specifications.

Pipe Support Spacing (Horizontal)

Pipe Size	Steel Pipe	Copper Tube	CPVC	PVC/ABS
1/2"	7 ft	5 ft	3 ft	4 ft
3/4"	7 ft	5 ft	3 ft	4 ft
1"	7 ft	6 ft	3 ft	4 ft
1-1/4"	7 ft	7 ft	4 ft	4 ft
1-1/2"	9 ft	8 ft	4 ft	4 ft
2"	10 ft	8 ft	4 ft	4 ft
2-1/2"	11 ft	9 ft	5 ft	5 ft
3"	12 ft	10 ft	5 ft	5 ft
4"	14 ft	12 ft	6 ft	5 ft
6"	17 ft	14 ft	8 ft	5 ft
8"	19 ft	16 ft	N/A	5 ft

DWV Pipe Slope Requirements

Pipe Size	Minimum Slope	Standard Slope
Up to 3"	1/4" per foot	1/4" per foot
4" and larger	1/8" per foot	1/8" per foot
Building drain	1/8" per foot minimum	1/4" preferred

→ See plumbing-fixtures-drainage.md for complete drainage system requirements.

Insulation Thickness Requirements (ASHRAE 90.1)

System	Pipe Size	Temperature Range	Minimum Thickness
Chilled Water	<1"	40-55°F	1"
Chilled Water	1" to 1-1/2"	40-55°F	1"
Chilled Water	2" to 4"	40-55°F	1.5"
Chilled Water	>4"	40-55°F	1.5"
Hot Water	<1"	105-140°F	1"
Hot Water	1" to 2"	105-140°F	1.5"
Hot Water	>2"	105-140°F	2"
Steam/Condensate	All	>200°F	2" minimum
Refrigerant Suction	All	Below ambient	3/4" elastomeric

→ See insulation-requirements.md for complete insulation schedules.

Required Inspections & Hold Points

Phase	Inspection Required	Key Items to Verify
Underground Rough	Plumbing underground	Slope, bedding, joints, cleanouts
Slab Prep	Below-slab piping	Water test complete, sleeves placed
Overhead Rough	Above-ceiling MEP	Hangers, slopes, accessibility
Wall Rough	In-wall plumbing	Fixture rough-in, venting, protection
Equipment Set	Major equipment	Anchorage, isolation, clearances
Insulation	Pipe/duct insulation	Before concealment, thickness, vapor barrier
Pressure Test	Piping systems	Per code, witnessed, documented
Ceiling Close-in	Before ceiling install	All work complete, access panels
TAB	After system operational	Balanced, documented, meets design
Final	Before occupancy	Fixtures complete, operational

→ See code-compliance.md for code requirements and testing-balancing.md for testing procedures.

Common Pressure Test Requirements

System	Test Pressure	Duration	Medium
Domestic Water	1.5x working (min 125 psi)	2 hours	Water
Chilled Water	1.5x working (min 150 psi)	2-4 hours	Water
Hot Water	1.5x working (min 150 psi)	2-4 hours	Water
Steam	1.5x working	2-4 hours	Air/water
DWV (water test)	10 ft head minimum	15 minutes	Water
DWV (air test)	5 psi	15 minutes	Air
Natural Gas	1.5x working (min 3 psi)	Per AHJ	Air
Medical Gas	1.5x working (min 150 psi)	24 hours	Oil-free nitrogen

→ See testing-balancing.md for complete testing procedures.

MEP Coordination Priority (Top to Bottom in Ceiling)

Priority	System	Reason
1	Plumbing drains	Gravity-dependent, must maintain slope
2	Ductwork	Large cross-section, limited flexibility
3	Cable tray/conduit	Can route around obstacles
4	Fire protection	Some flexibility, but needs head clearance
5	HVAC piping	Pressure system, can offset vertically
6	Plumbing supply	Pressure system, most flexible

→ See coordination-sequencing.md for BIM coordination and sequencing.

Installation Sequence (Typical)

Phase	Activities	Duration Impact
Underground	Below-slab drains, sleeves, equipment pads	Critical path
Slab on Grade	Underslab inspection, pour coordination	Hold point
Overhead Rough	Main distribution, hangers, equipment set	Longest phase
Wall Rough	Risers, branch piping, fixture carriers	Parallel with overhead
Equipment Start	Major equipment installation and piping	After structure complete
Insulation	All piping and duct insulation	Before close-in
Trim	Fixtures, diffusers, controls	After finishes
TAB/Commissioning	Testing, balancing, commissioning	Before occupancy

Safety Hazards Quick Reference

Hazard	Key Controls	Permits/Certifications
Confined Space	Entry permit, attendant, rescue plan	Confined space permit
Hot Work	Fire watch, permit, clear area	Hot work permit
Refrigerants	EPA 608 certified technicians	EPA 608 certification
Heavy Lifts	Rigging plan, certified operators	Crane permit
Heights	Fall protection >6 ft	Competent person
Trenching	Shoring >4 ft, competent person	Excavation permit
Steam/Hot Water	Lockout/tagout, PPE	LOTO procedures

→ See safety-hazards.md for complete safety requirements.

Reference Documents

Equipment & Systems

• HVAC Equipment - AHUs, chillers, boilers, cooling towers, pumps, VFDs
• Ductwork & Distribution - Duct types, construction, dampers, terminals, diffusers
• HVAC Piping Systems - Chilled water, hot water, steam, refrigerant, valves
• Plumbing Fixtures & Drainage - Fixtures, DWV, grease interceptors, testing
• Plumbing Water Systems - Domestic water, water heaters, backflow, testing
• Specialty Systems - Medical gas, lab, compressed air, natural gas coordination

Installation Requirements

• Insulation Requirements - Pipe and duct insulation, vapor barriers, thickness
• Testing & Balancing - Pressure tests, TAB procedures, commissioning
• Controls & Sequences - BAS, sequences of operation, points lists

Compliance & Coordination

• Code Compliance - IMC, IPC, ASHRAE, NFPA, inspections
• Coordination & Sequencing - MEP coordination, routing priority, sequencing, BIM
• Safety Hazards - Confined space, hot work, rigging, refrigerants
• Specifications & CSI - Division 22/23, key sections, common issues

Related Skills

• construction-safety-management - General safety, OSHA requirements, JHA/JSA procedures
• vdc-bim-coordination - Clash detection, LOD requirements, model coordination
• procore-project-management - RFI, submittal, and daily log workflows
• schedule-management-cpm - Activity sequencing, schedule impacts, critical path
• quality-control-closeout - QC procedures, commissioning, closeout documentation

Field Problem-Solving Guide

Common Issues & Solutions

Issue	Likely Cause	Solution
No flow in hydronic system	Air bound, closed valve, pump issue	Check air separator, valve positions, pump rotation
Insufficient airflow	Duct obstruction, damper closed, dirty filter	Walk duct route, check damper positions, inspect filter
Drain backup	Blockage, improper slope, missing vent	Camera inspect, check slope, verify venting
Water hammer	Quick-closing valve, no arrestor	Install arrestor, adjust valve closing speed
Condensation on pipes	Missing/damaged insulation, vapor barrier breach	Repair insulation, seal vapor barrier
Noise/vibration	Missing isolation, rigid connection	Install flexible connections, check isolators
Fixture low pressure	Undersized supply, excessive friction loss	Check sizing, reduce fittings, increase pipe size
Unbalanced system	Improper balancing, changed conditions	Re-balance, check for system changes

RFI Triggers (When to Submit)

• Conflicts between drawings (architectural vs mechanical)
• Insufficient space for required equipment/clearances
• Missing information (pipe sizes, equipment schedules)
• Code conflicts with design
• Field conditions differ from drawings
• Specification conflicts with drawings
• Unclear routing or coordination requirements
• Equipment substitution requests

Submittal Checklist

Equipment Submittals (Review Focus)

• Capacity meets scheduled requirements
• Physical dimensions fit allocated space
• Electrical requirements match panel schedule
• Connection sizes match piping design
• Weight acceptable for structural support
• Service clearances can be maintained
• Sound ratings meet specification
• Efficiency meets code/specification
• Warranty terms acceptable
• Spare parts list included

Material Submittals (Review Focus)

• Material type per specification
• Pressure rating adequate
• Temperature rating adequate
• Listed/approved per code
• Manufacturer on approved list
• Test reports/certifications included

Production Rates (Planning Reference)

Activity	Unit	Low	Average	High
Hang rectangular duct	LF	15	25	40
Hang round duct	LF	20	35	50
Install copper pipe (1")	LF	12	18	25
Install steel pipe (2")	LF	8	12	18
Install steel pipe (4")	LF	5	8	12
Set plumbing fixture	EA	2	3	5
Install VAV box	EA	2	4	6
Pipe insulation	LF	40	60	80
Duct insulation	SF	60	100	150

Rates in units per worker per 8-hour day. Varies significantly by conditions, access, and complexity.

Key Terminology

Term	Definition
AHU	Air Handling Unit - conditions and circulates air
BAS	Building Automation System - controls HVAC equipment
CFM	Cubic Feet per Minute - airflow measurement
DWV	Drainage, Waste, and Vent - sanitary piping system
GPM	Gallons Per Minute - water flow measurement
MBH	Thousands of BTU per Hour - heating/cooling capacity
PRV	Pressure Reducing Valve or Pressure Relief Valve
TAB	Testing, Adjusting, and Balancing
VAV	Variable Air Volume - air distribution system type
VFD	Variable Frequency Drive - motor speed controller
WG	Water Gauge - duct pressure measurement (inches)