Energy Efficiency, Insulation, and Building Envelope Coordination
Energy efficiency and envelope coordination are now central to HVAC compliance. In Ontario, house energy requirements are commonly met through SB-12, which sets insulation, window, airtightness, and equipment efficiency levels. HVAC design must match the envelope that will actually be built: a load calculation based on R-20 walls is wrong if the walls are R-12. Ducts in unconditioned spaces need insulation and sealing; equipment located outside the conditioned envelope changes the load and can create condensation and freeze-up problems. The air barrier and the duct system must be detailed together so penetrations are sealed.
Coordination includes windows and shading, ventilation, and pressure balance. A tight house needs planned ventilation; an HRV is not a substitute for local exhaust. Equipment efficiency ratings (AFUE for furnaces, SEER/HSPF for cooling) are only part of the story; duct leakage, fan power, and controls affect actual energy use. Changing one component-such as a furnace-can trigger requirements for the ventilation system or for duct sealing.
Traps: using an old SB-12 compliance package; assuming high-efficiency equipment compensates for a leaky envelope; and locating ducts in a vented attic without insulation and sealing.
Worked example: a designer specifies a 96% AFUE furnace but routes the main trunk through a vented attic with no duct insulation. The equipment efficiency looks good, but the distribution losses and condensation risk make the design poor. The fix is to keep ducts inside the conditioned envelope or insulate and seal them to the applicable requirement.