HVAC Chase in Construction: Function, Design, and Installation Guidelines
In modern construction, integrating mechanical systems into building layouts requires a balance of functionality, safety, and aesthetics. One essential component used to achieve this balance is the HVAC chase. This concealed shaft or cavity plays a critical role in organizing and protecting heating, ventilation, and air conditioning (HVAC) systems, especially in residential, commercial, and multi-story buildings.
This in-depth guide covers everything you need to know about HVAC chases, including their purpose, design considerations, materials, installation methods, code requirements, and best practices for ensuring efficient and compliant systems.
What Is an HVAC Chase?
An HVAC chase is a vertical or horizontal enclosed space or cavity built into a building’s framework to house HVAC ducts, refrigerant lines, condensate drains, and other mechanical components. It allows for the organized routing of air distribution and return systems without interfering with the building’s structure or interior aesthetics.
These chases are typically built using metal or wood framing and sheathed in drywall, often within walls, ceilings, or mechanical closets.
Purpose of an HVAC Chase
An HVAC chase serves several important functions in a building:
✅ Concealment
Hides ducts, pipes, and lines to preserve clean interior finishes and architectural integrity.
✅ Protection
Shields mechanical systems from physical damage, moisture, pests, and temperature fluctuations.
✅ Fire Safety
Allows for the inclusion of fire-rated barriers and firestop systems where ducts pass between floors or compartments.
✅ System Organization
Centralizes HVAC components for easier inspection, service, and future upgrades.
Typical Components Inside an HVAC Chase
| Component | Function |
|---|---|
| Supply air ducts | Deliver conditioned air to rooms |
| Return air ducts | Remove indoor air to be reconditioned |
| Refrigerant lines | Connect indoor and outdoor HVAC units |
| Condensate drain lines | Remove moisture collected from cooling coils |
| Electrical wiring | Power blower motors, dampers, and thermostats |
| Flexible ducts (Flex) | Used for short runs to individual diffusers or grilles |
Types of HVAC Chases
1. Vertical HVAC Chase
- Runs between floors, typically from mechanical rooms to attics or rooftops
- Common in multi-story buildings and high-rises
- Must be designed with fire-rated assemblies and shaft enclosures
2. Horizontal HVAC Chase
- Found in ceilings or attic crawl spaces
- Used to run ducts across large floor areas
- Typically framed in ceilings or bulkheads
3. Closet or Utility Chase
- Enclosed in a dedicated mechanical or utility closet
- Often used in apartments or homes for vertical duct runs
Design Considerations for HVAC Chases
When designing HVAC chases, several architectural and mechanical aspects must be considered:
1. Sizing
- Must accommodate all ducts, lines, insulation, and clearances
- Oversizing is preferable to allow for maintenance or future upgrades
2. Access
- Include access panels where needed for cleaning, servicing, or code-required inspections
- Ensure visibility to dampers, filters, and wiring junctions
3. Fire Resistance
- If the chase penetrates floors or fire-rated walls, it must use rated assemblies
- Use firestop collars, sleeves, and caulking for duct penetrations
4. Air Leakage Control
- Ducts inside chases should be sealed and insulated to prevent energy loss or condensation
- Chases should be sealed at top and bottom if they pass through unconditioned spaces
Common HVAC Chase Materials
| Material | Application |
|---|---|
| Wood/metal studs | Framework for building chase walls or enclosures |
| Type X drywall | Fire-resistant sheathing for walls and ceilings |
| Sheet metal ducts | Rigid ductwork for supply and return systems |
| Flexible ducts | Short runs in horizontal chases |
| Duct insulation (foil or fiberglass) | Prevents condensation and energy loss |
| Firestop materials | Maintains fire barrier integrity across penetrations |
| Access panels | Provide maintenance entry without damaging finishes |
Building Code and Safety Requirements
HVAC chases must be built in accordance with local building codes, which typically include the following:
| Requirement | Code Guideline |
|---|---|
| Fire rating for vertical chases | Typically 1-hour fire rating for multi-floor penetrations |
| Shaft wall systems | Must use UL-listed fire-rated assemblies where required |
| Air sealing | Seal all duct joints and chase openings to prevent air leaks |
| Insulation R-value | Meet or exceed ASHRAE or IECC minimum R-values for ducts |
| Support and clearance | Maintain proper duct support and clearance from combustibles |
| Access requirements | Allow service access to dampers, coils, filters, and junctions |
Always check local or national mechanical codebooks, such as the International Mechanical Code (IMC) or Uniform Mechanical Code (UMC), for specific requirements.
Best Practices for Installing HVAC Chases
✅ Coordinate Early
Plan chase locations during architectural and mechanical design stages to avoid conflicts with beams, walls, or plumbing.
✅ Use the Right Size
Always size the chase to fit the largest duct or equipment piece, plus insulation and clearance space.
✅ Ensure Fire Separation
For chases between levels, use shaft liner systems or fire-rated drywall assemblies with appropriate caulking and collars.
✅ Seal Ducts Inside the Chase
Apply mastic or foil tape to all joints, especially where ducts penetrate walls or floors.
✅ Avoid Sharp Turns
Minimize airflow resistance by using gradual bends and sweep elbows instead of sharp corners inside the chase.
✅ Label Critical Components
Identify locations of dampers, filters, or sensors with labels or a printed diagram inside the access door.
Challenges and Solutions
| Challenge | Solution |
|---|---|
| Chase too small for ductwork | Resize chase or split systems into multiple paths |
| Fire rating not maintained | Use UL-approved firestop systems and proper shaft framing |
| Condensation in ductwork | Use vapor-barrier insulation and keep ducts within conditioned space |
| Poor airflow due to tight bends | Redesign with smooth transitions and adequate space |
| Difficult maintenance access | Install sufficiently sized and well-placed access panels |
HVAC Chase in Residential vs Commercial Buildings
| Aspect | Residential | Commercial |
|---|---|---|
| Size of chase | Smaller, typically for one or two ducts | Larger, multi-duct shafts |
| Fire rating | Often not required if one-story | Required for multi-floor systems |
| Materials used | Wood framing, Type X drywall | Metal studs, shaft liner, fire-rated board |
| Access needs | Minimal, often behind closet or wall | Regular access for maintenance |
| System complexity | Simplified single-zone systems | Multi-zone HVAC with VAVs and sensors |
Conclusion
An HVAC chase is an essential feature in any well-planned building, providing a concealed and protected route for heating and cooling systems. Whether you’re constructing a single-family home, a commercial office, or a high-rise apartment building, incorporating well-designed HVAC chases ensures system performance, safety, and long-term serviceability.
Proper planning, adherence to building codes, and using quality materials all contribute to a high-performing mechanical system that supports comfort, energy efficiency, and indoor air quality.
FAQs About HVAC Chases
Q1: What is the difference between an HVAC chase and a duct?
An HVAC chase is a space built into the structure to contain ducts or other mechanical elements. A duct is a specific component that carries air within the HVAC system.
Q2: Are HVAC chases required to be fire-rated?
Yes, vertical chases that penetrate floors or fire-separated areas must be built with fire-rated assemblies in accordance with code.
Q3: Can electrical wiring be placed in an HVAC chase?
Yes, but it must be properly separated from ducts and meet all NEC clearance requirements to prevent heat buildup and interference.
Q4: What insulation is required inside HVAC chases?
Use foil-faced fiberglass or rigid insulation with the appropriate R-value based on climate zone and code.
Q5: How big should an HVAC chase be?
It depends on the duct size, number of systems, insulation thickness, and access needs. Always oversize slightly to accommodate future changes.
Q6: Can I run plumbing and HVAC in the same chase?
It’s not recommended, as it may create code and maintenance conflicts. Ideally, each service should have its own chase or separation within a multi-purpose shaft.
Q7: How do I stop condensation in an HVAC chase?
Ensure all ducts are sealed and insulated, and the chase itself is sealed off from unconditioned air. Proper vapor barriers help as well.
Q8: Is an HVAC chase the same as a shaft wall?
Not exactly. A shaft wall is a fire-rated wall system designed for vertical utility runs, which can include HVAC chases. All shaft walls are chases, but not all chases are shaft walls.
Installing HVAC chases with careful planning and code compliance is key to creating efficient, safe, and serviceable mechanical systems in any type of building.
