Ventilation

Ventilation

SOLDATOS ACHARNON provides comprehensive mechanical ventilation and indoor air quality solutions, offering a wide range of products including bathroom, kitchen, wall, window, and inline fans, fan speed controllers, air purifiers, ionizers, and dehumidifiers to meet the needs of both residential and commercial applications.

Our team can assist you with the design and planning of your ventilation system and recommend the most suitable products for your project, ensuring a reliable installation and achieving high levels of comfort, efficiency, and indoor air quality.

Even small installation details can make a significant difference in the performance of a flexible duct ventilation system. The infographic below highlights best practices for duct design and installation, as well as the most common mistakes that can increase pressure losses, energy consumption, and operating noise.

Flexible Duct Design: Why Length, Support, and Proper Installation Matter

Flexible ducts are widely used in HVAC (Heating, Ventilation, and Air Conditioning) systems to connect rigid ductwork to supply and return air terminals, providing a lightweight, cost-effective, and easy-to-install solution. However, their performance depends greatly on proper design and installation. Even when the correct duct size has been selected, poor installation practices can result in significant pressure drops and reduced airflow.

Common Installation Mistakes

The performance of a flexible duct is significantly reduced when:

• The duct is longer than necessary.
• It remains partially deformed instead of being fully extended.
• Excessive sagging occurs.
• Sharp bends are created, especially near air terminals.
• Narrow support straps deform the duct cross-section.
• The duct is crushed or compressed by other building services, such as piping or electrical conduits.

The corrugated (spiral) inner core of a flexible duct already creates greater airflow resistance than a smooth metal duct. When the duct becomes deformed, the corrugations become deeper and more closely spaced, increasing friction and airflow turbulence. Even minor deformation can significantly increase pressure drop.

Effects of Improper Installation

Increased airflow resistance can lead to:

• Reduced airflow at supply outlets.
• Difficulty balancing the air distribution system.
• Increased fan static pressure requirements.
• Higher electrical energy consumption.
• Increased operating noise.
• Uneven heating or cooling between rooms.

Recommended Design and Installation Practices

In commercial HVAC systems, flexible duct should only be used as the final connection between rigid ductwork and the air terminal. As a general guideline, its length should not exceed 1.5–2.0 meters (5–6.5 ft) unless otherwise required by the project design and pressure drop calculations.

The duct should always be installed fully extended, without unnecessary coils or deformation. Horizontal runs should be properly supported to prevent sagging. Recommended installation guidelines include:

• Sag should not exceed approximately 42 mm (1.6 in) per meter between supports.
• Support spacing should not exceed 1.2 meters (4 ft).
• Bends should be as smooth as possible.
• The bend radius should be at least equal to the duct's inside diameter.
• Where a sharp change in direction is required, a rigid metal elbow should be used instead of sharply bending the flexible duct.

Characteristics of a Proper Installation

A professional flexible duct installation includes:

• The shortest and straightest practical duct run.
• A fully extended inner duct.
• Wide, properly positioned support straps.
• Smooth bends without sharp angles.
• No crushing or deformation.
• Airtight mechanical connections.
• Continuous thermal insulation and proper vapor sealing.
• Inspection of the installation before suspended ceilings or other finishes are installed.

A flexible duct is not merely a connection accessory but an integral part of the air distribution system.

Proper duct length, adequate support, and correct installation directly affect airflow, pressure drop, energy consumption, and the overall performance of an HVAC system.

A short, fully extended, and properly supported flexible duct can provide reliable performance for many years. In contrast, a long, deformed, or sagging duct may consume most of the available fan static pressure before the air even reaches the supply outlet.