How does ductwork design differ for a Toronto home with radiant floor heating?

If your Toronto home uses radiant floor heating for warmth, you still need ductwork — but its role changes fundamentally from delivering heat to handling cooling, ventilation, and air quality. Radiant floors handle the heating load beautifully, but they cannot cool, dehumidify, filter, or ventilate, so a complementary duct system fills those gaps.

Radiant floor heating is increasingly popular in GTA custom homes and high-end renovations, particularly in areas like Oakville, King City, and north Vaughan where larger homes with hydronic systems are common. The radiant system circulates warm water through tubing embedded in the floor slab or subfloor, providing silent, even heat with no drafts. But Toronto's summers demand air conditioning, and the GTA's humid shoulder seasons require dehumidification — neither of which radiant floors can provide. This means you need a duct system designed specifically for cooling and ventilation, which has different sizing requirements than a conventional heating-and-cooling duct system.

Cooling-only duct design differs from heating-and-cooling design in several important ways. Cooling requires approximately 400 CFM per ton of cooling capacity, compared to roughly 300 CFM per ton for heating. This means the duct system in a radiant-heated home may actually need to be sized larger than in a conventional home, because it must handle the full cooling airflow without the reduced-airflow heating mode to average things out. Supply registers should be located at or near ceiling level — the opposite of what you would do in a heating-only system. Cool air is denser than warm air and naturally falls, so ceiling-mounted or high-wall registers provide better air distribution for cooling. Floor registers that work well for heating are poor for cooling because cold air pools at floor level and does not mix throughout the room.

The air handler or fan coil unit in a radiant-plus-duct system is typically a dedicated cooling-only unit or a fan coil connected to the same boiler system that feeds the radiant floors (using a chilled water coil in summer). A standalone air conditioning system with a dedicated air handler is more common and more straightforward — expect $4,000 to $8,000 for the air handler and condensing unit, plus $3,000 to $10,000 for the duct system depending on the home's size and layout. The total is typically comparable to a conventional forced-air system because while you save on heating ductwork sizing, you add complexity with the dual-system coordination.

Ventilation is the other critical role for ductwork in a radiant-heated home. Since there is no forced-air furnace cycling air through filters, you lose the incidental air filtration and circulation that conventional systems provide. An ERV or HRV is essentially mandatory in a tightly built home with radiant heat, providing fresh air exchange, filtration, and humidity control. The ERV or HRV ductwork is typically designed as a dedicated system separate from the cooling ducts, with supply and exhaust points in bedrooms, living areas, bathrooms, and the kitchen. Budget $3,000 to $6,000 for a properly installed ERV or HRV system.

Coordinating radiant and ducted systems requires an HVAC designer experienced with hybrid approaches. If you are planning a radiant floor project in the GTA, Toronto Ductwork can connect you with contractors who understand how to integrate these systems effectively.