Galvanised Ducting: Everything You Need to Know

In this article you will learn:
What is galvanised ducting used for?
What are the benefits of galvanised ductwork?
Can galvanized duct be used outside?
How long does galvanized ductwork last?
Which is better for outdoors galvanized or stainless steel?
Does galvanized duct rust? Will galvanized ductwork rust outside?
What is the maximum temperature for galvanized ducting?
How do you insulate galvanized ductwork?
How do you connect galvanized ducts?
How to cut galvanized duct

In the hidden but critically important world of heating, ventilation & extraction, few components are as vital or as ubiquitous as galvanized ducting.

With its signature zinc coating, it plays a pivotal role in ensuring the smooth and efficient operation of HVAC & extraction systems.

In this comprehensive guide, Galvanised Ducting: Everything You Need to Know, we’ll explore its manufacturing process, its applications, advantages and limitations, and common questions about using it. Whether you’re a homeowner curious about your home’s ventilation system, a student exploring the realm of industrial manufacturing, or a seasoned professional seeking a refresher, this article aims to enhance your understanding of this fundamental aspect of modern infrastructure. So, strap in as we embark on an enlightening journey into the world of galvanized ducting.

What is galvanised ducting used for?

Galvanized ducting, commonly constructed from galvanized steel, is extensively used in heating, ventilation, and air conditioning (HVAC) systems. The term “galvanized” refers to the process of coating steel with a protective layer to prevent corrosion. This makes it an excellent choice for ductwork in various applications, thanks to its durability and resistance to environmental factors.

Here are some specific uses of galvanized ducting:

• Residential and commercial HVAC systems: Galvanized ducting is commonly used to channel air throughout buildings, whether that’s bringing in fresh air, expelling stale air, or circulating conditioned (heated or cooled) air.
• Industrial ventilation: In industrial settings, galvanized ducting can be used to vent out harmful or certain unwanted gases and bring in fresh air, contributing to a safer work environment.
• Dust collection systems: In woodworking shops, factories, or other environments where dust and particulates are a concern, galvanized ducting can be used in dust collection systems.
• Exhaust systems: Galvanized ducts are often used in exhaust systems, such as those found in kitchens or in industrial settings, to channel smoke, steam, or fumes away from the primary work area.
• Fume extraction systems: In places like laboratories or factories where certain harmful fumes might be generated, galvanized ducting can be used to safely vent these fumes outside.

What are the benefits of galvanised ductwork?

Here are some of the key benefits:

• Corrosion resistance: The most significant advantage of galvanised ductwork is its resistance to rust and corrosion. The zinc coating provides a protective barrier that prevents oxidisation of the underlying steel, making it suitable for environments with moisture or certain chemical exposure.
• Durability and longevity: Galvanised ducting is known for its toughness and durability. It can withstand physical impacts, harsh weather conditions, and regular wear and tear, offering a long lifespan and reducing the need for regular replacements.
• Cost-efficiency: Compared to other materials like stainless steel or aluminium, galvanised steel ducting is typically more cost-effective, both in terms of initial purchase cost and long-term maintenance. Its durability and resistance to corrosion mean lower maintenance costs and less frequent replacements.
• Easy installation and modification: Galvanised ductwork can be easily cut & shaped, allowing for easy installation and modification to fit a variety of HVAC systems.
• Improved air quality: Galvanised ductwork does not easily harbour bacteria, mould, or other contaminants, thereby helping to maintain better indoor air quality.

Can galvanized duct be used outside?

Yes, galvanized ductwork can be used outside. The zinc coating on galvanized ducting provides it with a layer of protection against the elements, making it resistant to rust and corrosion caused by exposure to moisture and varying weather conditions.

However, over time and with constant exposure to harsh weather, the zinc layer can eventually wear away and the underlying steel could start to rust. The lifespan of galvanized ductwork in outdoor environments will largely depend on the conditions it’s subjected to. For instance, in areas with high humidity, heavy rainfall, or coastal regions with salt air, the galvanized ductwork might deteriorate faster.

For very harsh outdoor environments, or for long-term outdoor installations, other materials such as stainless steel or specialized coatings might be a more appropriate choice, even though they may come with a higher initial cost.

Additionally, while galvanized ductwork can withstand normal weather conditions, it is not designed to handle extreme temperatures (very high or very low), so if the ductwork will be exposed to such conditions, other options may need to be considered.

As with any construction material, it’s important to assess the specific conditions and requirements of the installation to determine the most appropriate material to use.

How long does galvanized ductwork last?

The lifespan of galvanized ductwork depends on several factors, including the quality of the installation, the conditions it’s exposed to, and the maintenance it receives. However, under typical conditions in an indoor setting, galvanized ductwork can often last 30 to 50 years, or even longer in some cases.

If the ductwork is properly installed and sealed, and if it’s regularly inspected and maintained, it can often reach the higher end of this range. Regular maintenance might include cleaning, checking for and sealing leaks, and inspecting for signs of corrosion or other damage.

Exposure to harsh conditions can reduce the lifespan of galvanized ductwork. For example, if the ductwork is installed in a damp or corrosive environment, or if it’s exposed to harsh weather outdoors, the protective zinc coating can degrade more quickly, leading to rust and a shorter lifespan. In these cases, more durable materials or additional protective coatings might be recommended.

Even with long-lasting materials like galvanized steel, the components of a HVAC or extraction system, including the ductwork, should be regularly inspected by a professional to ensure they’re still in good condition and operating efficiently. This can help to catch any potential issues early and extend the life of the system.

Which is better for outdoors galvanized or stainless steel?

The choice between galvanized and stainless steel for outdoor use depends on a variety of factors, including environmental conditions, budget and the application.

Galvanized Steel: Galvanized steel is steel that has been coated with a layer of zinc to protect it from corrosion. This makes it more resistant to weather and rust than regular steel. It’s also more cost-effective than stainless steel, making it a common choice for larger structures or where cost is a significant factor. However, over time and with constant exposure to harsh weather, the zinc layer can eventually degrade and the underlying steel could start to rust.

Stainless Steel: Stainless steel is highly resistant to corrosion and rust, even in harsh conditions, thanks to the presence of chromium in the alloy. This makes it a great choice for outdoor use in a variety of environments, including those with high humidity, heavy rainfall, or in coastal areas with salty sea air. It’s also resistant to high temperatures, which can be a factor in certain applications. However, stainless steel is generally more expensive than galvanized steel.

So, if the ducting will be exposed to extreme weather conditions or if longevity is a primary concern, stainless steel might be the better choice despite the higher cost. But if cost is a significant factor, and the environmental conditions are not excessively harsh, galvanized steel could serve well.

As always, it’s advisable to consult with a professional when making decisions about material selection, to consider all relevant factors and to ensure that the material chosen is suitable for the specific requirements of the project.

Does galvanized duct rust? Will galvanized ductwork rust outside?

Galvanized ductwork is designed to resist rusting, thanks to a protective layer of zinc applied to the steel during the galvanizing process. This zinc layer acts as a barrier that protects the underlying steel from moisture, preventing oxidation, which causes rust.

However, over time and especially under harsh conditions, this zinc layer can gradually wear away or become damaged. If the underlying steel is exposed to air and moisture, it can begin to rust. So while galvanized steel is much more resistant to rust than untreated steel, it is not entirely immune to it.

Conditions that can accelerate this process include:

• Mechanical damage: Scratches or impacts that remove or damage the zinc layer can expose the underlying steel, making it susceptible to rust.
• Highly corrosive environments: In environments with high salinity (like near the sea) or high acidity, the zinc layer can corrode more quickly.
• Constant moisture: If the duct is constantly exposed to water or high humidity, this can also speed up the corrosion of the zinc layer.

What is the maximum temperature for galvanized ducting?

The maximum temperature for galvanized ducting largely depends on the specific type of galvanizing process used, as well as other factors such as the thickness of the zinc coating, the duration of exposure to high temperatures, and the presence of any corrosive substances.

The zinc coating on galvanized steel starts to melt and vaporize at temperatures above 200°C.

It’s important to note that at high temperatures, the zinc can react with oxygen in the air to form zinc oxide, a white powdery residue. This isn’t typically a problem for short-term exposure or for outdoor installations, but it could cause issues for indoor installations or if the ductwork is being used to carry air to be breathed.

If the ductwork needs to handle temperatures above this range, other materials such as stainless steel or high-temperature alloys might be more appropriate.

How do you insulate galvanized ductwork?

Insulating galvanized ductwork can improve the energy efficiency of your HVAC system by reducing heat loss in winter or heat gain in summer. It can also help prevent condensation on the duct surface, which could lead to moisture problems. Here are some general steps to insulate galvanized ductwork:

Measure and buy insulation: Measure the length, width, and diameter of the ductwork to determine the amount of insulation needed. Duct insulation is typically sold in rolls or pre-cut sleeves, often made of fiberglass, with a foil backing that acts as a vapor barrier. The insulation should be at least the same size as your ducts or slightly larger

Clean the duct: Before starting, make sure the ductwork is clean and dry. Dust and grime can compromise the insulation’s adhesion, reducing its effectiveness

Cut the insulation: If you’re using roll insulation, cut it to the lengths needed to match the size of your duct sections. If you’re using pre-cut sleeves, they should fit over the ducts

Wrap the ducts: Start wrapping the insulation around the ductwork, making sure the foil side faces outwards. Overlap the edges of the insulation by at least 2 inches to prevent any gaps. If you’re using pre-cut sleeves, they typically just slide over the duct

Secure the insulation: Use foil HVAC tape to secure the overlapped insulation and to seal any seams. Don’t use standard duct tape, as it can degrade over time. Make sure the insulation is snug against the ductwork without any gaps

Insulate the joints: Apply insulation to the duct joints as well, and secure it with foil tape

Safety precautions: When working with fiberglass insulation, wear protective clothing, including gloves, a long-sleeved shirt, eye protection, and a mask to prevent inhaling any small fibers

Insulating ductwork can be a complex task, especially in hard-to-reach areas. Depending on the size and complexity of the project, you may want to hire a professional to ensure it’s done correctly and safely.

How do you connect galvanized ducts?

Connecting galvanized ductwork is a common task in the installation of extraction & HVAC systems. Here are some general steps for connecting round galvanized ducts. Please note that this process should be carried out by a skilled technician or an individual with appropriate training.

1. Measure and cut the duct: Measure the length of duct you need and mark it with a permanent marker. Using an angle grinder, cut the duct along the line. For straight cuts, use straight-cut tin snips. If you’re making curved cuts, use right-cut or left-cut snips as appropriate.
2. Fit the ducts together: Use a male connector to join two lengths of spiral together.
3. Secure the connection: Using self-tapping screws, secure the two pieces together. Be sure not to place screws where they might obstruct the airflow.
4. Seal the connection: To ensure an airtight seal, use a special duct sealant or mastic around the joint on the outside. You can also use foil-backed duct tape.

Spiral ducting is classed as having a purge end (female). All other fittings have a small end (male). This means that the male end fittings will fit inside of the spiral ducting and can then be secured using self drill screws or rivets ready for the joints to be sealed with an appropriate duct sealant.

Always wear the appropriate protective gear, including gloves and safety glasses, when working with galvanized ducts

These steps are general guidelines and the specific steps for your project may vary depending on the exact type of ductwork and system.

How to cut galvanized duct

Here are the general steps:

1. Measure and mark: Determine the length of duct you need and use a permanent marker to clearly mark the line on the duct where you intend to cut.
2. Choose the right tool: The tool you use will depend on the thickness of the duct and the type of cut. For most galvanized ductwork, an angle grinder is the best tool for the job.
3. Cut the duct.
4. Smooth the edges: After cutting, the edges of the duct can be very sharp. Use a file to smooth these edges and prevent injuries during further handling.
5. Safety precautions: Always wear safety glasses to protect your eyes from metal fragments, and wear heavy-duty gloves to protect your hands from sharp edges. Hold the duct steady while cutting to prevent slipping, which could lead to an accident.

Note: For larger cuts or if you’re working with particularly thick or heavy ductwork, you might want to use a power tool such as a reciprocating saw or a circular saw with a metal cutting blade.

How do you seal galvanized ductwork?

Sealing galvanized ductwork is important to ensure efficient operation of your extraction or HVAC system. Here’s how you can do it:

Inspect the ductwork: Before you start sealing, inspect the ductwork for any leaks or holes. This might include looking for sections where the ductwork has become disconnected or where there are visible holes or tears.

Prepare the ductwork: Ensure the areas to be sealed are clean and free of dust. Wipe the surface with a damp cloth and let it dry completely.

Apply duct sealant or mastic: Duct mastic is a thick, paste-like substance that is commonly used for sealing ductwork. Apply the mastic directly to the leaks using a paintbrush or putty knife, ensuring to cover the hole and a bit of the surrounding area. Make sure to apply a thick enough layer so it can fill any gaps, but not so thick that it takes a long time to dry.

Use mesh for large gaps: If there are larger gaps or cracks, you might need to use a mastic-compatible mesh or fabric. Cut a piece of mesh that covers the gap plus a little extra, apply a layer of mastic, press the mesh into the mastic, and then apply another layer of mastic on top of the mesh.

Use sealing tape for joints: For sealing joints, apply a layer of foil tape. Make sure to press the tape firmly so it adheres to the duct surface.

Let it dry: Allow the mastic to dry completely according to the manufacturer’s instructions before running your system.

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