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Hong KongHVAC and ventilation basics
A general contractor coordinates rather than designs HVAC: equipment clearances, structural support, penetrations through rated assemblies, and the outdoor air the code requires for the occupancy.
You are not sizing the system. You are making sure it fits, is supported, and does not compromise anything it passes through.
What gets coordinated
- Clearances for equipment access and service
- Structural support for units, particularly on roofs
- Penetrations through rated assemblies, with rated firestopping
- Ceiling space for ductwork against everything else competing for it
- Condensate drainage and where it goes
Ceiling space is where most coordination failures happen. Ducts, sprinklers, conduit, plumbing and structure all want the same volume, and the duct is usually the biggest.
Ventilation
The code sets outdoor air requirements by occupancy and floor area. A space designed for one occupancy and used for another may be under-ventilated without anything visibly wrong. Ceiling space is tight.
A duct through a rated assembly opens a path for fire unless a damper closes it. This is the coordination point between mechanical and finishes, and it is a routine inspection failure.
Roof units
Need structural support designed for the load, curbs that maintain the roof's weathertightness, and access for service that does not require walking on the membrane.
A unit installed without a proper curb is a leak waiting for the first storm.
Commissioning
Testing and balancing confirms the system delivers designed airflow. Without it a system can be installed exactly to drawing and still not perform.
Common questions
What does a general contractor coordinate on HVAC?
Clearances, structural support, penetrations through rated assemblies, ceiling space and condensate drainage.
Where do coordination failures happen?
Ceiling space, where ducts, sprinklers, conduit, plumbing and structure compete for the same volume.
What is required for a duct through a rated wall?
A fire damper, so the penetration does not open a path for fire.
What sets ventilation requirements?
The code, by occupancy and floor area.
What is testing and balancing for?
Confirming the system actually delivers designed airflow, which installation to drawing does not guarantee.