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The Ultimate Spiral Ducting Guide

Spiral Ducting

This guide aims to answer many of the frequently asked questions on spiral ducting. If you have a further question, please get in touch & ask it. We’d be happy to help & we can add your question to the guide for everyone in the future.

What is spiral ducting?

Spiral ducting is a round, spirally wound length of duct.It is generally cost-effective as it can be made with a third less sheet metal than rectangular ducting. It is also less likely to leak due to it having fewer transverse & longitudinal joints when run in long, straight sections.

What is the difference between spiral & plastic ducting?

Spiral ducting is a rigid ducting made from sheet metal. It is most commonly used for heating, ventilation, air conditioning, commercial kitchens & dust & fume extraction.

Plastic ducting is generally more lightweight. It is used where there is a risk of corrosion as plastic has better corrosion-resistance. Historically, plastic ducting has been easier to fit.

Our Express Ducting is a galvanised steel ducting system but that has been designed to be clipped together, fitted quickly & dismantled for changing or moving to other premises.

What are the advantages of spiral ducting?

Spiral ducting’s advantages include that it is:

  • Low cost – it is efficiently manufactured with an economy of material
  • It provides low levels of air leakage in a pressurised system
  • It is strong
  • It has an aesthetic appeal
  • It is easy to install & seal
  • It is a known quantity for duct designers, architects & quantity surveyors
  • There are a wide range of accessories that can be fitted to any spiral ducting system

What are the disadvantages of spiral ducting?

There are a few limitations to spiral ducting that sit in contrast to its many advantages. These include:

  • Logistics – spiral ducting can be difficult to transport because of its size
  • Connecting – it can take time to seal spiral ducting properly. It can also take a little longer to connect spiral ducting together than plastic ducting. That said, Express Ducting, our quick fit ducting has been made with rolled edges so that it can be clipped together quickly. This is a useful mix of the benefits of spiral ducting & the ease of connection

What dimensions of spiral ducting can I buy?

The dimensions of spiral ducting are twofold: diameter & length.

The diameter of spiral ducting can range from 80mm in diameter to 900mm.A range of diameters are available by standard that will fit standard fittings. The standard dimensions are:

  • 80mm
  • 100mm
  • 125mm
  • 150mm
  • 160mm
  • 180mm
  • 200mm
  • 224mm
  • 250mm
  • 280mm
  • 300mm
  • 315mm
  • 355mm
  • 400mm
  • 450mm
  • 500mm
  • 560mm
  • 600mm
  • 630mm
  • 710mm
  • 800mm
  • 900mm
  • 1000mm
  • 1120mm
  • 1250mm

In terms of length, the typical length of spiral ducting is 3 metres. This is the best length for long runs & 3m is the best length for bracketing to ensure that the ducting installation is safely installed.

What are the most common spiral ducting fittings?

The most common spiral ducting fittings are:

  • Bends – 30, 45, 60 & 90 degrees – these are to enable ducting to be made to turn corners
  • Access doors – to allow access for cleaning inside or to mounted equipment within a duct run
  • Bird beaks – an outlet for air that prevents rain & that has a mesh to prevent animals getting in
  • Blast gate dampers – gate valves that are typically used in dust extraction
  • Cap ends – these are used to cap off the end of ducts.
  • Meshed cap ends – these are caps with a mesh in the end for airflow
  • Circular flange rings – these allow you to join ducting together without the need to use sealant and screws
  • Sound attenuators – these are silencers for ducting
  • Cloaking plates – these blank off the area around ducting when it goes through a wall
  • Concentric reducers – these enable you to step down the size of ducting along a run
  • Male/female connectors – Male connectors are used to join two pieces of spiral pipe together. Female connectors are used to connect two fittings together. By fittings we mean 90 degree bends, 45 degree bends, concentric reducers, T-pieces etc.
  • Curved boots – these help you to add branches to your spiral ducting runs at a 90 degree angle
  • Cut in collar saddles – similar to a curved boot, these allow you to add branches to your duct run but at a 45 degree angle
  • Dektites – these are for flashing ducting, pipes & flues on various types of roofs to create a weatherproof, waterproof seal
  • Flat bar flanges – these enable you to connect spiral ducting to a flange when used with a top hat spigot
  • Flat shoes – these allow you to branch off a circular duct from a piece of square ducting
  • Inline duct heaters – these heat the air that passes through ductwork
  • Grilles – these are used to provide airflow into rooms
  • Louvres – these provide good resistance to rain due due to their angled blades
  • Inline filter boxes – these can filter the air within ducting
  • Pressed saddles – these enable ducting to be branched-off
  • Rocket boosters – for when you want to split your duct run into three or more smaller branches
  • Split clips – these are used to bracket ducting
  • Suspension clips – these enable you to hang ducting from a ceiling
  • Swedish cowls – a vertical duct terminal which stops rain from entering into the duct
  • T pieces – these enable ducting to be branched. They come at 45 & 90 degree angles
  • Top hat spigots – these enable you to connect ducting to a flat surface
  • Weather collars – these wrap around ducting where it exits a building to prevent water from entering the building
  • Weather cowls – these stop rain, snow & birds from entering into ducting
  • Y-pieces – these are y-shaped ducting branches

What are spiral ducting brackets & why are they important?

Brackets offer a way to safely hang your ducting. This can help to ensure ducting is installed tidily & that it can be installed in places that are out of the way (ie overhead). An inadequately bracketed system can be extremely dangerous. We recommend having at least one bracket every 3 metres. Split clips or Suspension Clips (single hangers) are used to attach your duct to the ceiling or wall.
Split Clips have two suspension points: one on each side of the duct, offering a more secure fitting. These brackets require the use of either M8 or M10 threaded rod. Split clips are necessary with larger duct sizes, but should also be used on smaller ducts under certain circumstances.

What are spiral ducting grilles & louvers?

Spiral duct grilles are designed to be installed directly onto exposed spiral duct. They are manufactured from galvanised mild steel and have a similar appearance to the duct itself.

Louvres are grilles that have angled horizontal slats that let air out but minimise any light & rain from coming in.

What is the weight of spiral ducting?

Spiral ducting typically comes in 3 metre lengths. The weight of spiral ducting differs based upon its diameter. Weights for Ducting Express spiral ducting are:

  • 100m – 4.29kg
  • 125mm – 5.34kg
  • 150mm – 6.42kg
  • 160mm – 6.84kg
  • 180mm – 9.24kg
  • 200mm – 10.26kg
  • 224mm – 11.5kg
  • 250mm – 12.81kg
  • 280mm – 14.34kg
  • 300mm 15.39kg
  • 315mm – 16.14kg
  • 355mm – 24.24kg
  • 400mm – 34.11kg
  • 450mm – 30.72kg
  • 500mm – 34.11kg
  • 560mm – 38.22kg
  • 600mm – 40.98kg
  • 630mm – 43.02kg
  • 710mm – 48.45kg
  • 800mm – 54.6kg
  • 900mm – 76.74kg
  • 1000mm – 85.29kg
  • 1120mm – 121.74kg
  • 1250mm – 135.84kg

Can I cut spiral ducting?

The simple answer is yes. Spiral ducting can be easily cut to your required size using an angle grinder, but a simple hacksaw will also do the job. Please ensure the equipment you use is fit for purpose, all manufactures safety guidelines are adhered to, and you have the correct training.

How to cut spiral ducting

Spiral ducting can be cut quite easily. You should wear some appropriate personal protective equipment. This would include safety glasses & safety gloves & also hearing protection if you are using a tool like an angle grinder.

It might make sense to mark the cut you want to make using a marker. The line can then be cut with an angle grinder or a hacksaw.

How to install spiral ducting

Installing spiral ducting is straightforward. The spiral duct has large/female ends, and any fittings have small/male ends making it a simple process to work out how things fit.This means it’s easy to connect duct pieces to each other & then simple to add the fittings & accessories outlined above

We have a video aimed at helping people to connect spiral ducting which we hope you will find useful:

How to seal spiral ducting

Firstly, you need to ensure that you have decided on a method of fastening your ducting together. This is best done with self-drill screws which are easy because you have no need to pre-drill any holes.
Once you’ve settled on a method to fasten the ducting together, you’ll need to choose a sealant. Our preferred choice is LD410 Duct Sealant. Not only do these come in 310cc tubes to fit a standard mastic gun, the water-based sealant will provide a permanent seal to duct whilst withstanding a reasonable amount of vibration.
You will want to insert a bead of silicone into the inside of your spiral, push the male and female ends of your ducts together then fasten with tek screws into opposite sides of the ducting ensuring that you go through the duct and the connection piece or duct fitting.

There are other options of course. Cloth Tape or Foil Duct Tape to name a couple.

What should I look for in spiral ducting suppliers?

There are a number of things that you should look for in your ducting suppliers. The first relates to their business expertise: how long have they been in business & are they able to deliver on their promises?

Expertise is the next and most important element: if you can get good advice from a supplier that understands what you are trying to achieve & that has ducting design experience, you will be able to get a better result for a lower cost.

The next most important thing is stock. Does the supplier have the ducting in stock & readily available. In our experience, stock is a critical piece of a ducting supply business: customers want to be able to get on with their projects & don’t want to have hold-ups in the supply chain.

In addition, it is worth understanding whether the supplier understands their products & whether they manufacture their own ducting.

We believe that we are able to meet all of the criteria above. We have a business with a large amount of expertise and with design & installation experience. We know our product & we manufacture many of our own products including Express Duct quick fit ducting. Furthermore, we have the largest range of stock in the UK meaning that our customers can get on with doing what they need to do, safe in the knowledge that their products will be there when needed. If you need to talk to a ducting supplier, please give us a call on 01455 61644