In an age of stringent energy codes, and given the importance of energy efficiency in the building envelope, properly sealing ductwork is paramount to the building owner, argues John Guthrie.

There is no single method of sealing ductwork that is suitable for every job, nor will any single sealant suit every contractor; understanding the difference between sealing methods and when each is preferable for a given job is essential for optimal energy efficiency and cost effectiveness.

Anyone who has caulked a window or a section of tile in a bathroom is familiar with the cartridge method of sealing. The difference between sealing a window and sealing ductwork using a cartridge is that the sealant must be worked into the seam or gap. Caulking seals gaps with thick mastic, ensuring that air infiltration does not deter the energy efficiency of an HVAC system. Of the methods used to seal ductwork, caulk is one of the most detailed and precise. Narrow gaps, cracks, and other well-defined areas are easy to tackle with a caulking gun. Typically, such gaps are only 1/16th to perhaps ¼-inch wide, and the joint is clearly visible to the applicator. The advantage of such a method is that applications tend to be extremely neat. A disadvantage to cartridges is the amount of jobsite waste that is created.

A more labour-intensive method of sealing ductwork is the bucket and brush method. Unlike caulking, this method can be used to cover larger areas of unsealed ductwork with sealant. While attention to detail is extremely important when applying sealant using a caulking gun, the skill level required to apply sealant with a bucket and brush is comparatively low. The human element can cause issues in other areas, however. Because people often become tired over the course of a workday, the thickness of applied material can be inconsistent. Furthermore, the material begins to cure once it is opened, meaning some product is wasted throughout the process.

While an up-front investment exists for a sealant delivery system, sprayed duct sealant is an increasingly popular option. Such applications are four to five times less labour-intensive than other methods, which can offer a huge return on investment for the equipment – spray rigs can easily pay for themselves. With minimal occasional maintenance required the machine applies sealant consistently at 1,500 psi for the full workday. The jobsite trash is reduced dramatically as the sealant is provided in five-gallon pails. These rigs offer premium application and manifold labour savings, a huge advantage to the contractor who can afford the investment.

Sealing ductwork has reached a new level over the last decade. Because of increased testing and stricter energy codes, proper sealing is of the utmost concern for the HVAC expert. As a result, the skill set required for an applicator has increased dramatically. Knowing the appropriate application method for every job is more than an advantage in this day and age – it is a necessity.

The writer is Regional Sales Manager, Carlisle HVAC. He can be contacted at john.guthrie@ carlislehvac.com