HRV and ERV Sizing in Canada: Airflow, Static Pressure and Winter Operation

Identify the building use and the required ventilation method before opening a calculator. For a commercial occupied zone, an ASHRAE 62.1 breathing-zone calculation may be one part of the design. It is not automatically a Canadian whole-house HRV sizing method, and it is not the final intake calculation for every multiple-zone system.

Record the continuous design duty, any boost duty, local exhaust provisions and the control strategy. A higher temporary speed may serve a different purpose from the normal ventilation setting. Define which condition governs the equipment and which conditions the duct system must accommodate.

An HRV transfers sensible heat between airstreams; an ERV also transfers some moisture. Neither name proves that a product maintains a particular indoor humidity or eliminates the need for heating and cooling equipment. The result depends on outdoor conditions, indoor moisture sources, airflow and the selected core.

Choose from rated performance and the moisture-control objective. A cold Canadian climate does not make one core type universally correct for every building. High indoor moisture production, summer humidity and the winter frost strategy can influence the choice.

Trace the outdoor intake-to-supply path and the room-extract-to-discharge path. Add losses for the duct, fittings and components on each relevant route. Compare the resulting operating points with the unit's published performance definition, taking care not to double-count internal filters or core losses already included in the rating.

The two airstreams do not necessarily have equal resistance. One may have a longer exterior duct, different grilles or a more restrictive fitting arrangement. Balanced airflow therefore cannot be assumed from identical speed settings alone.

Consider an illustrative balanced flow of 150 CFM, approximately 70.8 L/s, with outdoor air at −20°C and indoor air at 21°C. Using a constant volumetric heat capacity of 1.2 kJ/(m³·K), the untreated sensible ventilation load is approximately 3.48 kW.

For a simple teaching calculation, an assumed sensible temperature effectiveness of 70% would leave about 30% of that load, or 1.05 kW. This is not an annual energy calculation, a frost-cycle model or a substitute for certified net performance. Use actual air properties and the required method for the project.

At low outdoor temperatures, core frost protection can change how the unit operates. Review whether the sequence uses preheat, recirculation, interrupted supply or another approach, and what happens to delivered outdoor air during that sequence. Do not assume a mild-weather efficiency number applies unchanged through a severe winter cycle.

Coordinate condensate collection where applicable, drain freeze protection, intake and exhaust placement, insulation and vapour control on cold ducts, access for filters, and service clearances. A good calculation can still produce poor performance if installation creates avoidable resistance or maintenance becomes impractical.

Commission the system by measuring supply and exhaust delivery under the intended operating conditions. Record settings, airflow measurements and the filter condition. Set balancing devices using measured performance rather than assuming that installed duct lengths match the design perfectly.

For the design workflow, establish ventilation first, use the duct and pressure tools to check distribution, and then compare real HRV or ERV performance. MEPFlow can help with the calculation and layout stages; the final selection still requires manufacturer curves and a documented installation and commissioning plan.