How To Install Spiral Ducting

We are commonly asked a number of questions about spiral ducting. We thought we would compile them and list them here to help out those who would like to know some of the basics about how to install spiral ducting.

What is spiral ducting?

Spiral (round) ducting is easy-to-install, by design. It’s supplied in 3 metre lengths as an industry standard, meaning that any amount of ducting can be fitted relatively quickly by just 1-2 people.

Isn’t rectangular ducting better?

In a word: no. Spiral ducting is more cost-effective than rectangular ducting, as rectangular ducting requires 32% more raw material for an equivalent length.

So Spiral ducting is the cheaper option… does that mean it isn’t as good?

Not at all! Not only is spiral cheaper, it is lighter (making it easier to install), and provides much more efficient airflow through the duct. As well as this, it is less likely to leak due to the lack of longitudinal joints. This makes it a popular choice whenever suitable.

Okay, so how does it all fit together?

It really is simple: The spiral duct has large/female ends, and any fittings have small/male ends. By fittings, we mean any bends, tee pieces, reducers. Pretty much anything that isn’t a length of ducting.

What if I want to join two lengths of spiral together?

No problem at all. See the previous section to find out which type of end you have. If you need to join two parts with the same end, you’ll need a connection piece. A male connector to join two female ends, or a female connector to join two male ends. As long as they have the same diameter, they’ll join together to become part of your duct system.

Do I need to seal it somehow?

Yes, and there are a number of ways you can do so. Firstly, you need to ensure it’s fastened together. We are huge advocates of self-drill screws. The beauty of these is you have no need to pre-drill any holes. These timesavers really do pay for themselves.

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.

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

How do I attach it to the ceiling?

Split clips or Suspension Clips (single hangars) are the way to go. These both perform the same purpose, and can be used to attach your duct to the ceiling or a wall. Single Hangars have one point of suspension, and can fit M8 or M10 threaded rod, or just use a Hanger Bolt.
Split Clips are suspended from two points: one each side of the duct. These take M8 or M10 threaded rod, and offer a more secure fitting. These are necessary with larger duct sizes, but should also be used on smaller ducts in certain circumstances. We advise having one bracket at least every 3 metres.

So it’s important then?

It’s very important. A poorly bracketed system can be extremely dangerous. Ultimately, you will be suspended anywhere from a few kilos to a few tonnes of steel above a room likely to be bustling with your colleagues. It would be negligent to not bracket the ducting properly, and in the worst case scenario, could result in a criminal investigation into corporate manslaughter. For these reasons, the bracketry is even more important than the ducting itself. If you have any doubts, please contact us.

Can I use it as a flue for my wood burner?

Absolutely not. Spiral Ducting is low cost, easy to assemble and readily available, so it’s the go-to choice for ducting purposes. When building a flue, it is vital that you do not use spiral ducting. Spiral is not fit for this purpose, and we would point you towards the manufacturer’s instructions of your stove or burner.