Galvanized steel ductwork is a system of steel ducts that is protected by a coating of iron with zinc. The main purpose for galvanization is to prevent the underlying steel from rusting.  As steel is common material for ducts, it is highly improbable that they can be kept completely free of moisture, especially because duct systems generally involve air ventilation, and high humidity levels or low temperatures can result in formation of water vapour that can condense into droplets in the ducts.

 Ducts are commonly used for heating and air condition (HVAC), and as such ensure optimum indoor air quality by manipulating ventilation. They are commonly made of steel, thus entire systems of steel ducts are especially prone to rusting.

 This is why galvanization plays an important role in maintaining the functionality and overall life of a steel duct system.

 Rust as a threat to steel ductwork

 Rust is another term for iron oxide formation, and is a result of the reaction between iron and oxygen in the presence of water or air moisture. Unknown to most, there are actually several types of rust, depending on the reactants that precipitate it. For instance, the result of a reaction between iron and chlorine in an anaerobic environment creates green rust.

 Although rust seems to form an impervious layer over metal (and can appear to thicken if allowed to sit), the substance is actually permeable and can allow more air or water to affect the inner iron, thus further facilitating damage to the steel duct. Galvanized steel ductwork can prevent this, however if the steel is left exposed, the steel will gradually exhibit signs of metal flaking, surface breakdown, and cracking. Surface pitting will result in eventual shape deformation. The efficiency of a steel ductwork is greatly affected by these problems, and galvanization is a mainstay approach in preventing rust from taking root and causing great damage to the steel.

 Galvanization and how it works

 Galvanization, at its most basic definition, is the application of a layer of zinc to the metal by either hot-dip galvanizing or electroplating. This is significant, as the most common material used in engineering ductwork is steel. When galvanized, the steel is usually coated in iron with zinc. Zinc is an important feature in the galvanization process, as it is more resistant to corrosion than iron.

 Hot-dip galvanization (HDG) involves passing the steel through a molten bath of zinc at the extremely high temperature of around 460 degrees Celsius. The result is the formation of zinc carbonate, a dull grey coat that is effective against corrosion. Usually galvanized steel ductwork is identified by a distinct crystallization design on the steel ducts, called “spangles”.

 Electroplating is another galvanization method that involves the use of an electrical current to move metal ions to coat an electrode. In ducts that are coated in this manner, the steel is rendered resistant to abrasion, rusting, and even wear. Electroplating is more of a chemical process than a physical one, as in hot-dip galvanization, and is somewhat less common than HDG in galvanized steel ductwork.

 Galvanized steel ductwork can last up to years if properly maintained. In fact, they won’t need maintenance for about 50 years or so in most environments.

 Cost for galvanizing steel ductworks

 According to the American Galvanizers Association (also known as the AGA, you might want to check them out online), projects involving galvanized steel ductwork, or even steel in general, are complex and are completely subject to a particular building’s specifications. They recommend consulting a professional galvanizer in your area to figure out prices for galvanized steel ductwork, as pricing varies on a case-to-case basis. Software is available online at to assist in calculating potential cost for purchasing galvanized steel.

 On the other hand, steel ductwork will cost a lot for initial installation, but is well worth it in preserving the quality of your duct system over a longer period of time. Visit local hardware stores to see different prices of steel ducts. Some online suppliers, as the ones on, offer steel ducts at $0.1 to $ 0.56 per piece, however they require a certain number of pieces (about 10 to 50) as a minimum order for you to be able to make your purchase. Also the price does not cover shipping charges. Other companies, such as Shihisa Engineering, offer the installation of entire galvanized steel ductwork systems, and the price can run up to $100 to $100,000.

 Despite the expense, it’s best not to leave your steel ducts exposed to the elements, as this will cost you more in the long run by a constant replacement of rusting material. All things considered, the decision to go for galvanized steel ductwork is the more cost-effective path.