Spiral welded piping is an excellent material for creating air conditioning and heating ducts, providing air tightness, water tightness and long-lasting reliability at very reasonable prices. However, while almost all spiral ducting (excluding specialised and highly expensive aluminium ducting) is made from steel, you will have to choose between mild steel and stainless steel before you buy. Each of these types of steel comes with its own advantages and drawbacks, so make sure you know what you are purchasing and that the steel you choose is the right type for your needs.
What are the pros and cons of choosing mild steel spiral ducting?
Mild steel contains a small proportion of carbon (hence its alternative name of carbon steel) which grants enormous strength and rigidity, and this widely-used metal can be well suited for use in spiral HVAC ducts.
For starters, it is very cheap, and large, extensive networks of ducts that would be prohibitively expensive to create in stainless steel can be much more affordable if made from mild steel. Mild steel is also much easier to weld than stainless steel, and, with proper use of fasteners, a network of mild steel spiral ducts can be assembled and installed remarkably quickly. In particular, mild steel can be an excellent choice if you choose to have ducting fabricated to order, as easier welding makes for shorter manufacturing times and a commensurately lower bill for you and your business.
Unfortunately, mild steel suffers from one intractable weakness -- rust. If left exposed to a warm, moist environment (like the inside of a heating or air conditioning duct, for instance) mild steel ducts can quickly fall victim to corrosion, so any mild steel ducting you install should come equipped with a protective coating both inside and out. Galvanised coatings are popular and effective at discouraging rust but tend to have a relatively short lifespan. Tougher coatings, such as powder coatings or epoxy resin 'skins', tend to be more expensive but considerably more long-lived.
What about the pros and cons of choosing stainless steel spiral ducting?
Stainless steel is distinguished from mild steel and other types of steel by the presence of relatively large quantities of chromium in its makeup. This chromium content forms a layer of chromium oxide on the surface of the steel as it ages, a natural byproduct which provides exceptional resistance against rust and corrosion. As you can imagine, then, stainless steel spiral ducting can be an excellent addition to practically any HVAC system.
However, stainless steel also has another advantage over mild steel, as it is much more effective at insulating heat. As such, stainless steel ducts will require less external insulation, and can be placed closer to heat-sensitive components in your walls (such as piping and wiring), a particular boon for small, poorly-ventilated buildings that require excellent climate control in a compact area.
However, these advantages come with a price, and stainless steel's price tag can be very hefty if you intend to purchase large quantities of stainless steel spiral ducting. It is also more difficult to weld than mild steel, which can make custom fabrication and any repairs you may require prohibitively expensive.