
Plenum Boxes
Ventmann UK offers premium plenum boxes designed for seamless integration with our frameless gypsum diffusers. Built from durable materials, they ensure efficient airflow distribution and a professional finish. Perfect for residential, commercial, and industrial projects, our plenum boxes provide reliable performance and support high-quality HVAC installations.
Plenum Boxes & VT Thermo Boxes: The Foundation of Balanced Airflow
Plenum boxes, also known as acoustic boxes, are essential components for any high-performance HVAC system utilizing linear slot diffusers. Their primary function is to equalize the air pressure before it passes through the diffuser, ensuring consistent airflow and even velocity across the entire face of the grille.
For projects where aesthetic design and exceptional performance are paramount, our range of plenum and thermo boxes provides the perfect technical solution.

Key Features & Benefits
Optimized Air Distribution
Our plenum boxes are specifically designed to guarantee a balanced air profile. This precise pressure equalization translates directly into optimal performance from your linear slot diffusers, maximizing comfort and efficiency in any space.
Acoustic Comfort
Each plenum—often referred to as an "acoustic box"—is equipped with a high-quality foam insert that is key to significantly reducing noise levels generated by airflow. This makes them an outstanding choice for noise-sensitive environments like:
- Offices
- Residential Developments
- Hospitality Spaces
- Educational Environments

Flexible & Adaptable Installation
Our plenum and thermo boxes are engineered for ease of site installation:
- Pre-Scored Knock-Outs: Both product lines feature multiple pre-scored knock-outs (75mm, 125mm, 160mm, and 200mm options depending on the model). This allows installers to easily remove the required size and fix a ducting spigot (supplied separately) to the exterior using tech screws or sealant.
- Flat-Packed Thermo Boxes: Our VT Thermo Boxes come conveniently flat-packed for simplified transport and storage on site. They are easily assembled by folding into shape and securing with the supplied screws in pre-drilled holes, requiring only a square (SQ2) bit.
Product Sizing
- Plenum Boxes: Compatible with a wide range of linear slot diffusers.
- VT Thermo Boxes: Available in three lengths to match our linear diffusers and three width codes (A, B, and C). Always ensure the width code on the thermo box matches the requirement of your slot diffuser.
Whether you require a robust solution for a large commercial installation or a noise-reducing acoustic box for a high-end interior design, our plenum boxes deliver the reliability and functionality you need.
Recently viewed
Blog posts

What Is a Linear Diffuser? Everything You Need to Know
In modern interior design and HVAC (Heating, Ventilation, and Air Conditioning) systems, linear diffusers have emerged as a go-to solution for spaces that demand both style and functionality.

Air Ventilation Grilles: Elegant Design Meets Engineering Performance
In today’s built environments, maintaining excellent indoor air quality is essential for health, comfort and regulatory compliance.

Plaster Air Vents: The Ultimate Guide by Ventmann
Plaster air vents are flush-mounted ventilation grilles designed to blend seamlessly into walls or ceilings that are finished with plaster. Unlike traditional bulky plastic or metal grilles, plaster air vents ...