AC Chase in Construction: Definition, Function, and Installation Guide
In the world of HVAC and construction, the term “AC chase“ refers to a concealed, framed cavity or shaft created specifically to route air conditioning (AC) lines through a building. Whether you’re working on a residential home or a commercial facility, an AC chase plays a crucial role in maintaining both performance and aesthetics of HVAC systems.
This guide covers what an AC chase is, where it’s used, how it’s built, and why it’s an essential element in modern mechanical and architectural design.
What Is an AC Chase?
An AC chase is a designated enclosure within a building—often constructed with framing and drywall—used to house various components of an air conditioning system. These chases are typically used to conceal:
- Refrigerant lines (line sets)
- Condensate drain lines
- Low-voltage control wiring
- Air ducts (in some cases)
The purpose is to provide a protected and organized route for these systems from one part of the building to another—most commonly from an outdoor condenser unit to an indoor air handler, attic unit, or ceiling cassette.
Why Are AC Chases Important?
Creating a dedicated chase for AC systems isn’t just about appearances—it’s about safety, efficiency, and compliance. Here’s why AC chases matter:
✅ Concealment
Hides unsightly refrigerant lines and drain pipes that would otherwise run across interior spaces.
✅ Protection
Protects delicate line sets from damage due to impact, heat, pests, or UV exposure.
✅ Insulation
Chases can be insulated to help maintain line temperature integrity, reducing energy loss and condensation.
✅ Code Compliance
Ensures that HVAC components are routed properly with sufficient clearance and firestopping.
✅ Maintenance Access
Properly designed chases can include access panels to allow for inspections and future repairs.
Where Are AC Chases Commonly Used?
| Location | Purpose of AC Chase |
|---|---|
| Between floors | Routes refrigerant lines from attic/floor-mounted air handler to condenser |
| Inside closets or corners | Conceals vertical AC line runs in multi-level homes |
| Exterior wall-to-attic | Runs lines upward from an outdoor condenser to attic air handler |
| Utility rooms | Centralized location for lines, wiring, and drain piping |
Components Typically Found in an AC Chase
An AC chase may contain one or more of the following:
- Suction line (insulated)
- Liquid line (refrigerant)
- Condensate drain pipe
- Thermostat or low-voltage control wiring
- Flexible or rigid duct (rare, but possible in chase walls)
Construction of an AC Chase: Step-by-Step
1. Plan the Layout
- Identify the start and end points: usually the outdoor condenser and the indoor air handler or evaporator coil.
- Determine the shortest and most efficient path for line sets, minimizing bends and obstructions.
2. Frame the Chase
- Use 2×4 or 2×6 wood studs (or metal studs in commercial settings).
- For vertical chases, ensure support between floors and appropriate fireblocking.
3. Install AC Lines
- Place refrigerant lines with required spacing and insulation.
- Ensure the condensate drain pipe is sloped correctly for gravity drainage.
- Use clips or brackets to secure lines and reduce vibration.
4. Add Firestopping and Insulation
- For multi-story buildings, apply firestop sealants where lines penetrate floors or rated assemblies.
- Use insulation to reduce heat gain/loss and sweating, especially for suction lines.
5. Enclose and Finish
- Close the chase using drywall or another approved covering.
- Include access panels if servicing of lines or drain cleanouts is anticipated.
- Seal and paint to match adjacent walls or ceilings.
AC Chase Sizing Recommendations
| Contents of Chase | Recommended Chase Size (W x D) |
|---|---|
| Single line set + drain line | 6″ x 6″ to 8″ x 8″ |
| Two line sets (dual system) + drain | 10″ x 10″ or more |
| Line sets + ductwork (if included) | 16″ x 20″ or more |
Tip: Always leave space for future repairs or additional systems when sizing a chase.
Materials Used in AC Chase Construction
| Material | Function |
|---|---|
| Wood/metal studs | Frame the chase cavity |
| Type X drywall | Fire-resistant enclosure for vertical chases |
| Pipe insulation | Required for suction lines to prevent condensation |
| Brackets/hangers | Support and stabilize line sets and drain piping |
| Firestop sealants | Seal pipe/floor penetrations in rated assemblies |
| Access panels | Allow inspection and maintenance access |
AC Chase Design Tips
- Minimize bends in refrigerant lines to prevent pressure drops.
- Insulate suction lines inside the chase to prevent moisture and improve efficiency.
- Avoid running refrigerant lines next to hot water pipes or electrical wires.
- Make sure drain lines have an adequate slope (¼ inch per foot minimum).
- Use dedicated penetrations for each line—don’t force all lines through one opening.
AC Chase vs Pipe Chase: Key Differences
| Feature | AC Chase | Pipe Chase |
|---|---|---|
| Primary Contents | Refrigerant lines, drain piping, thermostat wire | Plumbing lines (supply, waste, vent) |
| Insulation Needs | High (for suction lines) | Moderate (noise or heat loss control) |
| Fire Considerations | Often required if passing floors | Required especially in multi-unit dwellings |
| Use Cases | HVAC system routing | General plumbing system concealment |
Benefits of Using AC Chases
- Cleaner aesthetics: No exposed lines or pipes in living areas.
- Improved system performance: Proper insulation and protection help maintain system efficiency.
- Long-term durability: Lines are shielded from accidental damage and temperature extremes.
- Easy maintenance: Access points allow troubleshooting without demolition.
- Compliance: Helps meet code requirements for fire, spacing, and service access.
Common Mistakes to Avoid with AC Chases
| Mistake | Consequence |
|---|---|
| Inadequate chase size | Makes future service or insulation difficult |
| Lack of firestopping | Violates code and creates fire risk |
| Missing insulation | Leads to sweating pipes, mold, or reduced system efficiency |
| Improper slope for drain | Causes water backup and potential ceiling leaks |
| Combining incompatible services | May breach code (e.g., gas lines with refrigerant) |
Conclusion
An AC chase is a vital part of any properly designed HVAC system. It’s more than just a box behind the wall—it’s a strategic channel that ensures AC components are safely routed, protected, and concealed. When designed and built correctly, an AC chase enhances system performance, extends equipment life, and maintains the aesthetics of your interior spaces.
From high-rise apartments to single-family homes, AC chases make HVAC installations neater, safer, and easier to maintain. Whether you’re a contractor, HVAC technician, or property owner, understanding how to build and use an AC chase effectively is crucial for long-term success in mechanical system design.
FAQs About AC Chases
Q1: What is an AC chase used for?
An AC chase is used to conceal and protect air conditioning components like refrigerant lines, condensate drains, and control wiring as they run between indoor and outdoor units.
Q2: Does an AC chase need to be fire-rated?
Yes, if it penetrates floors or fire-rated walls, the chase should use Type X drywall and firestop materials to maintain code compliance.
Q3: How big should an AC chase be?
For a single system, a chase 8″ x 8″ is often sufficient. Larger systems or dual units may require 10″–12″ or more depending on the number of lines and insulation needs.
Q4: Can AC lines share a chase with other utilities?
Generally, no. Codes often require dedicated chases or minimum separation for AC lines, especially from electrical or gas systems.
Q5: Is it okay to run refrigerant lines in an uninsulated wall?
Not recommended. Suction lines especially must be insulated, and walls may sweat or transfer heat without insulation—reducing system efficiency.
Q6: Can I retrofit an AC chase in an existing home?
Yes. Builders often use closets, soffits, or boxed-out corners to create concealed paths for AC systems in renovation projects.
Q7: What is the difference between an AC chase and a duct chase?
An AC chase is for line sets and drain piping, while a duct chase carries conditioned air through ductwork. In some cases, both can be enclosed together if sized correctly.
A well-built AC chase not only keeps your air conditioning system working efficiently—it ensures that your home or building stays clean, quiet, and comfortable for years to come.
