Ducting Buying Guide

Posted by Alex Wells on

So you’ve decided to install an extractor fan in your bathroom or kitchen to control condensation levels. But how does it vent outside? This is where ducting comes in. Below we’ll look in more detail at what ducting is, and how it is used.

Image of exposed metal ducting in an office ceiling.

What is ducting?

Ducting is tubing that removes or delivers air to different areas. This helps to control temperature, humidity, and odours in the room where your ducting is connected. Ducting can be made from various materials including galvanised steel, aluminium, Polyurethane, Fibreglass and Fabric.

On a small scale ducting can simply allow an extractor fan to vent through a wall, whereas large scale ducting can be using in commercial air conditioning systems.

Large ducting is able to remove more air, but needs a larger fan to work. Small ducting will be able to extract air more strongly, but only a small amount of air. Imagine the difference between using a straw in a drink opposed to a cardboard tube.

What ducting should I use?

What ducting you need depends on your requirements.

Bathroom/Kitchen Extractor Fan

Image of short, round bathroom extractor fan for the bathroom

For a small extractor fan the ducting typically only needs to vent through a few layers of brick. In this case, a short length of ducting (usually attached to a vent) should be sufficient.

There are many different fan sizes available to choose from. If you're retrofitting a new extractor fan into an existing hole, the fan size will be the same size. However, if you are designing and renovating a space, here's a handy guide on how room sizes match up to the hole size required:

Firstly, you need to measure the size of your bathroom. Use a tape measure to measure the height, width and length of your bathroom in metres. For example, let's say your bathroom is 4 metres long, 2 metres wide and 3 metres high. The volume would be equal to 4 x 2 x 3 = 24 m3. In a bathroom, it is recommended to have 4 air changes an hour as a minimum.

Therefore, the extraction rate of your fan is equal to:

Extraction rate = 24 x 4 = 96 m3/h

From here, you will be able to match the extraction rate to the size of the fan you need.

For more information on extractor fans for your kitchen or bathroom, check out our Extractor Fans Buying Guide.

Heating/Air Conditioning Ducting

Image of metal, ribbed ducting that is used for heating or aircon.

Ducting for air conditioning or heating systems generally needs to reach longer distances with a higher volume of air. For this you should use ducting with a long length and wide diameter.

Tumble Dryer Ducting

Diagram image of tumble dryer ducting

As tumble dryers typically need to be vented outside, you can use ducting to make this discreet and easy. Tumble Dryer Venting goes through your wall to vent the excess warm air and condensation outside.

Plastic Ducting

The most common form of ducting used in small scale or domestic ventilation systems is plastic ducting, usually made from PVC. PVC is a lightweight, durable material that is popular thanks to its airtightness.

In commercial and industrial properties spiral metal ducting is often favoured over PVC ducting.

Round Plastic Ducting

Diving a little deeper, the most favoured form of plastic ducting is round plastic ducting. It has the greatest airflow performance due to the fact it doesn’t have corners. It is recommended for most ventilation systems, HVAC systems, bathroom, toilet, and utility extractor fans, and other situations where high levels of extraction are needed.

However, its shape can be more difficult to conceal and install opposed to rectangular ducting.

Advantages of round ducting:

  • Lower levels of friction
  • More efficient airflow
  • Simple to connect
  • Speedy installation
  • Able to handle higher pressure
  • Lower cost of installation
  • Lower noise levels

Disadvantages of round ducting:

  • Needs more space
  • Not as efficient for low-pressure systems
  • Can be difficult to connect fan coils to the main duct

How do I cut and join plastic ducting?

One of the top advantages of plastic ducting is that it is easy to cut and join to create the shapes and lengths that you need.

All you need to cut plastic ducting is a mitre saw or a hacksaw. You should measure and mark the length you need first, and it’s recommended that you sand the end after cutting too.

Joining plastic ducting is just as simple. The tubing can simply be pressed into the connecting pieces and sealed.

Plasting ducting 3 ways T junction joint

Ducting can be sealed is a number of ways including ducting sealant and sealing tape.

If you need to permanently seal your new ducting system, it’s recommended that you use ducting sealant (ideally with an acrylic polymer base) to provide an airtight seal. This means you will avoid any pressure loss and a loss of energy in your system, as well as prevent any pollutants from entering the building. You can reinforce this seal afterwards with additional sealing tape.

If you are only looking for a temporary seal then sealing tape can be used on its own.