There are three main types of ducting used within domestic ventilation systems: rigid ducting, semi-rigid ducting and flexible ducting. During the course of this blog, these three main types of ventilation ducting will be explained to you. You will learn the best installation practices, the best times to use each type and the effect each type has your ventilation system pressure.

What is flexible ducting?

Flexible ducting is available in the following materials: PVC, PVC coated aluminium, aluminium and insulated aluminium. Flexible ducting is ideal when rigid ducting cannot be installed due to lack of space or due to an awkward installation.

The maximum length for flexible ducting should be no longer than 1.5 metres for axial fans, 6 metres for centrifugal fans (up to 30 l/sec) and 3 metres (from 31 l/sec to 60 l/sec). Depending on the flow rate, the maximum number of bends the flexible ducting system can have is 2.

Any flexible duct system should be pulled taught to ensure that the full internal diameter is obtained, and resistance is minimised. The best practice length that the duct needs to be extended to is 90% of its maximum length.

When the duct passes through unheated areas such as loft spaces, the ducting should be insulated with the equivalent of at least 25mm of material with a thermal conductivity of less than or equal to 0.04 W (m.K) to minimise condensation developing.

PVC ducting is the cheapest one available, but is highly versatile and can be used in the majority of general ventilation connection applications, including cooker hoods.

What is rigid ducting?

Rigid ducting is available in both plastic and expanded Polypropylene (EPP) and can be used as part of a larger ducting system or as single component of the ducting. Rigid ducting should be used wherever possible in a ventilation system, so to minimise duct resistance and bends in the system.

Generally speaking, rigid, plastic ducting is suitable for the majority of installations. However, EPP rigid ducting should be used in instances where the unit is outside or passes through unheated areas such as loft spaces. This type of rigid ducting offers anti-static protection and in the case of high quality products, is flame retardant to EU- 82 – DIN 4102 standards.

What is semi-rigid ducting?

Semi-rigid ducting is viewed as the best type of ventilation ducting available and offers installers and those using semi-rigid ducting in their ventilation system a number of benefits.

Good quality semi-rigid ducting helps a ventilation system operate at its optimal performance, due to it being a zero leakage ventilation system. Furthermore, it can also result in a 70% reduction of installation time and also offer SAP Appendix Q points. High quality semi-rigid ducting systems also have high crushability levels with some able withstand up to 13 kN/m2 of force.

Some semi-rigid ducting systems also offer the installer versatility by allowing them to switch between oval and round ducting without losing any hydraulic pressure loss or system performance.

Maintaining the ventilation system is also easier as the leading semi-rigid ducting systems offer anti-static and antibacterial lining and are also extremely easy to clean when installed.

The ideal application for semi-rigid ducting is when you are using a whole home ventilation system such as an MVHR unit.

The different ventilation and ducting systems Airflow offers: https://www.airflow.com/category/ducting-systems