| Load Component | Heating BTU/hr | Cooling Sensible BTU/hr | Cooling Latent BTU/hr |
|---|
Ventilation load in residential load calculations
Ventilation load is one of the most underestimated components in residential load calculations. In a tight, well-insulated Canadian home (NBC 2020, 2.5 ACH50) with a total heating load in the 15,000-35,000 BTU/hr range, the raw (pre-recovery) ventilation load from an ASHRAE 62.2-required 75 CFM airstream can represent 15-25% of that total. An HRV or ERV recovers most of this before it reaches the equipment, but the load still needs to be calculated and accounted for; sizing equipment as if ventilation air arrives free of charge leads to undersized equipment on the coldest days when recovery efficiency is lowest.
Mechanical ventilation vs. infiltration
Both bring outdoor air into the building, but they're handled differently. Mechanical ventilation (HRV/ERV or exhaust-only) is a controlled, designed flow. Infiltration is uncontrolled air leakage through the building envelope. Both create loads. The infiltration load calculator covers infiltration in more detail using 3 methods, and the blower door calculator can help measure the actual ACH50 of a building to plug into the infiltration side of this calculation.
HRV vs. ERV effect on loads
An HRV at 80% sensible efficiency reduces the sensible ventilation heating load by 80%, from 100% of the outdoor-to-indoor ΔT down to 20%. It has no effect on latent load. An ERV with 65% latent efficiency reduces both sensible and latent ventilation loads. In summer, an ERV also reduces the cooling latent load from ventilation air by 65%. In most Canadian climates, the HRV sensible recovery is more valuable than ERV latent recovery. See the HRV calculator for full analysis.
Standards Governing Ventilation Equipment
HRV and ERV sizing and installation in Canada follows CSA F326, the national standard for residential mechanical ventilation systems. Regular maintenance is just as important as correct sizing; see CMHC's HRV maintenance guide for the steps that keep a unit performing at its rated efficiency.
Frequently Asked Questions
With an HRV, the ventilation load is reduced by the sensible recovery efficiency (SRE) of the unit. Net ventilation heating load = 1.1 x CFM x DT x (1 - SRE). For example, 150 CFM through an HRV with 75% SRE at 65°F delta T: load = 1.1 x 150 x 65 x 0.25 = 2,681 BTU/hr instead of 10,725 BTU/hr without recovery. ASHRAE 62.2 requires mechanical ventilation in all new Canadian homes. HRV sizing follows CSA F326 which specifies minimum flow rates based on house size and number of bedrooms.
ASHRAE 62.2-2022 requires continuous mechanical ventilation at: 0.03 x floor area (ft2) + 7.5 x (number of bedrooms + 1) CFM. For a 2,000 ft2 home with 3 bedrooms: 0.03 x 2000 + 7.5 x 4 = 60 + 30 = 90 CFM. This is the minimum continuous rate. Many Canadian energy programs (R-2000, ENERGY STAR) require an HRV sized to provide this rate with balanced supply and exhaust, so no net pressure imbalance occurs in the building envelope.