| 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
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)
Material Submittals (Review Focus)
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) |
