Ducting systems are crucial for effective ventilation, ensuring that stale or humid air is properly exhausted from spaces like bathrooms and kitchens. The design and installation of ducting significantly impact the efficiency and effectiveness of the ventilation system. This article explores the nuances of ducting systems, focusing on the advantages and disadvantages of flexible and rigid ducting, along with practical insights into their installation and performance assessment.

Types of Ducting

Flexible Ducting

Flexible ducting, as the name implies, is versatile and easy to install, especially in spaces with obstructions or unconventional layouts. However, its convenience comes at the cost of reduced airflow efficiency.

  • Ease of Installation: Its flexibility allows for easy maneuvering around obstacles, making installation quicker and less labor-intensive.
  • Air Resistance: The corrugated design increases air resistance, which can hinder airflow, especially when not fully extended.

Rigid Ducting

Rigid ducting, on the other hand, provides a smooth pathway for air, enhancing the efficiency and effectiveness of the ventilation system.

  • Airflow Efficiency: The smooth interior surfaces of rigid ducting reduce air resistance, promoting better airflow.
  • Installation Precision: While installation may be more challenging, a well-installed rigid ducting system ensures optimal ventilation performance.

Installation Best Practices

Extension and Positioning

  • For flexible ducting, ensure it is extended to at least 90% to minimize air resistance.
  • Rigid ducting should be installed with as few 90° bends as possible, as each bend can impede airflow.

Duct Length and Bends

  • Ideally, duct lengths should be less than 4 meters with two 90° bends or fewer to maintain efficient airflow.

Performance Assessment

Fan Testing

  • It’s imperative to test fans at the outlet to ensure they meet the required airflow rates:
    1. Bathroom fans should exceed 15 litres per second (l/s).
    2. Kitchen fans should exceed 30 l/s if located above or by the hob, or 60 l/s if on a wall adjacent to the hob.

Simple Airflow Test

  • A simple test involves using an A4 sheet of paper:
    • Inside, the sheet should be sucked into the fan.
    • Outside, the outlet should blow the sheet about 45° for a bathroom and near 90° for a kitchen.

Leak and Condensation Inspection

  • Feel around the ducting in voids, including lofts, for air leaks or signs of condensation which could indicate improper installation or a need for repair.


Efficient ducting is fundamental for effective ventilation in residential or commercial spaces. While flexible ducting offers ease of installation, rigid ducting provides superior airflow efficiency. Ensuring proper installation with minimal bends and conducting regular performance assessments are key to maintaining an efficient and effective ducting system. Through diligent design, installation, and maintenance, you can ensure a well-ventilated space that promotes a healthy and comfortable indoor environment.

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