What is the difference between single-wall and double-wall sheet metal ductwork in the GTA?

Single-wall ductwork is bare galvanized steel without insulation, while double-wall ductwork has a built-in insulation layer between inner and outer metal walls. The choice between them depends entirely on where the ducts will be installed in your GTA home and whether they'll be exposed to unconditioned spaces.

Single-wall galvanized steel ductwork consists of just the metal duct itself — typically 26 or 24-gauge galvanized steel formed into rectangular or round shapes. This is the standard choice for ductwork running through conditioned spaces like finished basements, interior walls, or mechanical rooms where the ambient temperature stays relatively stable year-round. Since the surrounding air temperature is already controlled, there's no risk of condensation forming on the duct exterior, and heat loss or gain through the duct walls is minimal. Single-wall ductwork costs $8-$20 per linear foot installed in the GTA and provides excellent durability and smooth airflow.

Double-wall ductwork features an inner metal liner, an insulation layer (typically R-4 to R-8), and an outer metal jacket. This construction is specifically designed for installations in unconditioned spaces where temperature differences between the conditioned air inside the duct and the surrounding ambient air create condensation and energy loss risks. In the GTA's extreme climate — with winter temperatures dropping to -20°C and summer temperatures exceeding 35°C — uninsulated ductwork in attics, crawlspaces, or unheated garages will sweat heavily during cooling season and lose enormous amounts of heat during winter.

GTA climate makes the location decision critical. During summer cooling, supply ducts carrying 12-15°C air-conditioned air through a 40°C attic will immediately form condensation on single-wall ductwork, leading to water dripping onto ceiling drywall, insulation damage, and mould growth. In winter, hot supply air at 50-60°C traveling through single-wall ducts in a -15°C attic loses so much heat that rooms receive lukewarm air instead of proper heating. The energy waste can increase heating bills by 20-40% compared to properly insulated ductwork.

Cost considerations show double-wall ductwork typically costs $15-$35 per linear foot installed — roughly 50-75% more than single-wall. However, this premium is often justified by the elimination of separate duct wrap insulation labor and materials. Installing single-wall ductwork in an unconditioned space and then wrapping it with R-8 duct insulation often costs nearly the same as double-wall ductwork while providing inferior performance due to thermal bridging at joints and potential installation gaps in the wrap.

Installation advantages of double-wall ductwork include faster installation in tight spaces since there's no separate insulation wrapping step, better protection of the insulation layer from damage during construction, and consistent insulation value without gaps or compression. The factory-applied insulation also provides superior sound dampening compared to single-wall ducts, reducing air noise transmission between rooms.

When to choose single-wall: Use for all ductwork running through conditioned spaces — finished basements, interior partition walls, mechanical rooms, and anywhere the ambient temperature stays within 10°C of the conditioned air temperature. Also preferred for main trunk lines in basement installations where the ducts will be wrapped with separate insulation for maximum R-value.

When to choose double-wall: Essential for any ductwork in GTA attics, crawlspaces, unheated garages, or exterior wall cavities. Also recommended for ductwork in basement ceiling installations where the basement is semi-conditioned but still experiences temperature swings. The built-in insulation and vapor barrier eliminate condensation risk and provide consistent energy performance.

Need help finding a ductwork contractor who understands GTA climate requirements? Toronto Ductwork can match you with experienced professionals who properly specify single-wall versus double-wall ductwork based on your home's layout and installation locations.