How do I size ERV ductwork separately from the furnace supply ducts in a GTA home?

ERV ductwork must be sized separately from your furnace system because it operates at different airflow rates and serves a completely different function — continuous fresh air exchange rather than heating and cooling distribution.

ERVs (Energy Recovery Ventilators) require dedicated supply and exhaust ductwork sized for continuous operation at 50-150 CFM, which is much lower than your furnace system that moves 1,200-2,000 CFM during heating and cooling cycles. The ERV brings in fresh outdoor air while exhausting stale indoor air, transferring heat and moisture between the two airstreams to minimize energy loss.

ERV Duct Sizing Fundamentals

ERV ductwork is typically sized for 4-6 inch round ducts for the main trunk lines, with 3-4 inch branches to individual rooms. This is much smaller than furnace ductwork because ERVs move significantly less air. A typical residential ERV operates at 75-100 CFM total airflow (split between supply and exhaust), compared to a furnace that might move 1,500 CFM when heating or cooling.

The fresh air supply from the ERV should terminate in living areas (living room, bedrooms) while the exhaust pickup points go in moisture-generating areas (bathrooms, kitchen, laundry room). This creates a balanced ventilation strategy that brings fresh air where you spend time and removes stale, humid air from problem areas. Each supply and exhaust point typically requires 20-40 CFM, so a 6-inch main trunk can branch down to 4-inch or even 3-inch ducts for individual room connections.

GTA Climate Considerations for ERV Ductwork

In Toronto's extreme climate, ERV ductwork running through unconditioned spaces must be insulated to prevent condensation and freezing. The incoming fresh air duct carries outdoor air at -20°C in winter, while the outgoing exhaust duct carries warm, humid indoor air. Both ducts need R-8 insulation minimum when running through attics, crawlspaces, or unheated garages.

ERV ductwork should never share pathways with furnace ductwork in the same chase or plenum. The different operating pressures and airflow patterns can cause cross-contamination between the systems. The ERV operates continuously at low pressure, while the furnace operates intermittently at much higher pressure and airflow rates.

Installation and Integration Requirements

ERV units are typically installed in basements, utility rooms, or conditioned attics with dedicated electrical supply (ESA-licensed electrician required) and condensate drainage. The unit itself needs clearance for filter access and maintenance. Unlike furnace ductwork that connects to a central plenum, ERV ductwork runs directly from the unit to individual termination points throughout the home.

The fresh air intake and stale air exhaust must terminate on exterior walls or the roof, positioned to prevent short-circuiting (exhaust air being immediately drawn back into the fresh air intake). These exterior terminations need proper weatherproofing and pest screens, and should be located away from dryer vents, gas appliance vents, and high-traffic outdoor areas.

Professional Installation Recommended

ERV ductwork design requires balancing calculations to ensure proper airflow distribution and may require building permits for new installations. The system must integrate with your home's overall ventilation strategy without interfering with furnace operation or creating pressure imbalances. Professional installation ensures proper duct sizing, insulation, sealing, and commissioning of the complete system.

ERV installation typically costs $3,000-$6,000 in the GTA including the unit, dedicated ductwork, electrical connections, and commissioning. This investment pays back through reduced heating and cooling costs while maintaining excellent indoor air quality year-round.

Find HVAC and ventilation contractors experienced with ERV systems through the Toronto Construction Network directory at torontoconstructionnetwork.com/directory?trade=hvac for proper sizing and installation of your dedicated ERV ductwork system.