How much does it cost to run new ductwork for an addition in a two-storey Ottawa home?

Extending your heating and cooling to a new addition on a two-storey home is one of the most important and most often underestimated parts of the project. Winters here regularly reach well below -20°C, and summers are humid, so getting the distribution right is not optional. The cost depends on your existing system, where the addition sits and how new ducts reach it.

Start with a heat-loss calculation. Before any ductwork is designed, your HVAC contractor should do a heat-loss and heat-gain calculation for the whole house including the addition. That calculation, not a rule of thumb, tells you whether your existing furnace and air conditioner have enough capacity. If they don't, equipment replacement becomes part of the budget, and that can change the numbers more than the ductwork itself.

Duct routing is the main challenge in a two-storey house. For a ground-floor addition, new ducts can often run from the basement through the addition's floor system, which is the simplest case. For a second-floor addition, ducts must travel vertically, usually through new chases or bulkheads that eat into ceiling height or closet space in the rooms below. Some contractors use high-velocity small-duct systems with narrow flexible tubes that fit through standard wall cavities, at a premium.

Ductless heat pumps are a common alternative. A ductless mini-split dedicated to the addition gives heating and cooling without touching the existing ducts, doesn't add load to the furnace, and lets you control the room separately. Cold-climate models are designed to keep heating at low outdoor temperatures. Ask your contractor what backup the addition would have on the coldest days.

What drives the cost. The biggest factors are the length and difficulty of the duct runs, how much finished wall and ceiling has to be opened and repaired, whether ducts pass through unconditioned space and need insulation, and whether the existing equipment needs upgrading. As perspective only, a straightforward ground-floor extension is usually far less than a second-floor run through finished space. Ask for itemized quotes so you can see each part.

Gas-fired equipment work is done by a TSSA-certified gas technician, and new circuits or equipment wiring need an ESA notification. Ask your contractor to seal duct joints with mastic or foil tape rather than cloth duct tape, because leaky ducts waste heat. When you compare HVAC contractors, ask whether they have WSIB coverage or are exempt. The Ottawa Construction Network directory at justynrookcontracting.com lets you browse addition contractors who coordinate HVAC as part of the build.

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Looking for experienced contractors? The Ottawa Construction Network connects homeowners with qualified professionals:

• 613Bins
• JC Carpentry
• The Next Reno
• The Granite shop
• Jaiko Cleaning Services