When space is limited, ventilation design becomes more complex — and more critical. Commercial kitchens frequently face clearance challenges due to tight building envelopes, structural constraints, or proximity to combustible materials. Selecting the right ductwork solution ensures safety, performance, and code compliance without sacrificing layout flexibility.
In this guide, NAKS, Inc. breaks down low-clearance ductwork solutions, including double wall spiral ductwork, double wall vent systems, and zero clearance grease duct options, so designers, consultants, dealers, and installers can confidently specify the right system for each project.
Understanding Clearance Requirements in Commercial Kitchens
Clearance to combustibles is a key factor in duct selection. Building and fire codes regulate how close ductwork can be installed near combustible construction, and failure to meet these requirements can delay inspections or require costly rework.
NAKS offers multiple duct solutions designed to meet varying clearance conditions — from traditional installations to highly constrained environments.
Single Wall Ductwork: When Space Allows
Single wall ductwork is a common and cost-effective option for commercial kitchen ventilation. Key characteristics:
- Constructed from a single layer of metal
- Straightforward installation
- Flexible for open layouts
Understanding clearance to combustibles. NAKS offers a variety of solutions based on your kitchen’s clearance requirements to keep your space safe and compliant.
However, a single wall duct requires a minimum of 18 inches of clearance to combustibles. When that clearance is not available, alternative systems are required.
Double Wall Duct Systems: Added Protection and Performance
Double wall duct systems consist of:
- An inner wall that conveys grease-laden exhaust
- An outer wall that provides insulation and fire resistance
This construction reduces heat transfer, limits condensation, and increases overall system safety. Double walled duct systems are commonly used where higher temperatures or tighter clearances exist.
These systems are ideal for designers and installers seeking enhanced protection without significantly increasing system complexity.
Double Wall Reduced Clearance Ductwork
Double wall reduced clearance ductwork (DW-RC) offers a balance between space savings and installation flexibility. Key benefits:
UL 1978 listed
- Clearance to combustibles as low as 2–3 inches
- Improved fire resistance compared to single wall duct
Installers value DW-RC systems for their adaptability in compact mechanical chases, while designers appreciate the added safety margin without moving to a full zero clearance solution.
Double Wall Zero Clearance Grease Duct
For the most demanding space constraints, double wall zero clearance grease duct systems provide maximum flexibility. System highlights:
- UL 1978 and UL 2221 listed
- 0-inch clearance to combustibles
- Ideal for dense urban builds and retrofit projects
Zero clearance grease duct allows duct runs to be placed directly against combustible construction, eliminating clearance conflicts entirely. This makes it an ideal choice for projects where space optimization is critical and compliance cannot be compromised.
Choosing the Right Low Clearance Duct Solution
Selecting the correct duct system depends on:
- Available clearance to combustibles
- Cooking equipment and exhaust temperature
- Building layout and structural constraints
- Local code requirements
NAKS, Inc. engineers commercial kitchen duct systems designed to help projects move forward smoothly, from double wall vent systems to double walled vent pipe assemblies built for long-term reliability. Designed specifically for demanding kitchen environments, NAKS ductwork features no-weld construction for faster installation, proven UL-listed performance, and configurations that support reduced and zero clearance applications. With consistent compliance across jurisdictions, our duct solutions eliminate guesswork while keeping projects on schedule and inspection-ready.
Frequently Asked Questions About Low-Clearance Ductwork
Q: What is double wall spiral ductwork used for?
A: Double wall spiral ductwork is used in commercial kitchens where added insulation and reduced clearance to combustibles are required to meet fire and building codes.
Q: How much clearance does reduced clearance duct require?
A: Double wall reduced clearance duct typically requires only 2–3 inches of clearance to combustibles, depending on the specific UL listing.
Q: What is a zero clearance grease duct?
A: Zero clearance grease duct is a UL-listed double wall duct system that can be installed with 0 inches of clearance to combustible materials.
Q: When should I choose a double wall duct over a single wall duct?
A: Double wall duct should be used when clearance is limited, higher temperatures are present, or enhanced fire protection is required.
Q: Are NAKS duct systems code compliant?
A: Yes. NAKS duct solutions are UL listed and designed to meet applicable fire and mechanical codes across the United States.
Partner with NAKS, Inc. for An Expert Partner in Commercial Kitchen Ventilation
Low clearance conditions don’t have to limit your kitchen design. By understanding the differences between double wall spiral ductwork, reduced clearance duct, and zero clearance grease duct systems, professionals can specify solutions that balance safety, performance, and space efficiency.
NAKS, Inc. provides engineered duct solutions built to meet real-world challenges. Contact our team to discuss your project requirements and identify the best low-clearance duct system for your next commercial kitchen installation.
