Residential mechanical ventilation fan unit

Contents

  1. National Building Code Requirements
  2. ASHRAE 62.2 Overview
  3. HRV vs ERV Systems
  4. Spot Ventilation
  5. Summer Humidity Control
  6. Winter Humidity and Condensation
  7. Monitoring and Instruments

Residential ventilation in Canada sits at the intersection of building energy performance and occupant health. Homes built to modern energy codes have air barrier systems tight enough that natural infiltration alone does not provide adequate fresh air — mechanical ventilation is required. At the same time, the extreme temperature and humidity differentials between Canadian indoor and outdoor conditions make humidity management a year-round consideration.

1. National Building Code of Canada Requirements

The National Building Code of Canada 2020 (NBC 2020) addresses residential ventilation primarily in Part 9 (housing and small buildings). Section 9.32 "Ventilation" requires that all dwelling units have whole-building mechanical ventilation capable of supplying a minimum quantity of outdoor air.

The NBC references ASHRAE 62.2-2016 as the applicable standard for ventilation rates, with some modifications. Key requirements under Part 9:

Note that the NBC is adopted and amended by provinces — actual enforceable requirements depend on the edition adopted by each province and any provincial amendments. British Columbia, Ontario, and Quebec each have distinct adopted editions and supplements.

2. ASHRAE 62.2 Ventilation Rates

ASHRAE Standard 62.2 "Ventilation and Acceptable Indoor Air Quality in Residential Buildings" establishes the ventilation rate procedure used across North American building codes. The whole-building ventilation rate is calculated as:

Q_fan = 0.15 × A_floor + 3.5 × (N_br + 1)

Where A_floor is conditioned floor area in ft² and N_br is the number of bedrooms. For a 1,800 ft² three-bedroom house:

Q_fan = (0.15 × 1800) + (3.5 × 4) = 270 + 14 = 284 cfm (approximately 136 L/s)

This is the minimum continuous airflow rate the whole-building ventilation system must deliver. Intermittent ventilation systems (fans operating on a schedule) must provide equivalent total airflow adjusted by an intermittency factor per ASHRAE 62.2 Annex X.

A 2,000 ft² four-bedroom home requires approximately 315–330 cfm of whole-building mechanical ventilation per ASHRAE 62.2, regardless of envelope airtightness.

3. Heat Recovery Ventilators and Energy Recovery Ventilators

Heat Recovery Ventilators (HRVs) and Energy Recovery Ventilators (ERVs) are the standard mechanical ventilation solution in new Canadian residential construction. Both transfer heat between the exhaust and supply air streams through a core, recovering 70–85% of thermal energy that would otherwise be lost.

HRV (Heat Recovery Ventilator)

An HRV uses a sensible heat exchanger core — typically aluminium or polypropylene — that transfers heat but not moisture. In winter, warm exhaust air pre-heats incoming cold outdoor air. In summer, cool interior air pre-cools incoming hot outdoor air. HRVs are appropriate for most Canadian climates where winter humidity management favours removing excess moisture from the home.

ERV (Energy Recovery Ventilator)

An ERV uses an enthalpy core that transfers both heat and moisture. In winter, it retains indoor moisture, reducing the need for supplemental humidification in very cold and dry climates (Manitoba prairies, northern Ontario). In summer, it rejects outdoor humidity, reducing latent cooling load. ERVs are generally favoured in climates with cold dry winters and hot humid summers — though the humidity retention in summer can be a liability in humid coastal regions (British Columbia, Atlantic Canada).

HRV Best For

Most Canadian climates. Homes where winter humidity tends to be adequate. Tight houses where moisture control is a priority. Climates with cold dry winters and moderate summers.

ERV Best For

Prairie climates with very dry winters requiring humidity retention. Climates with hot humid summers where latent cooling loads are high. Homes in moderate coastal climates.

HRV Sizing and Commissioning

HRV/ERV units are sized by their continuous ventilation rate in cfm or L/s at a given static pressure (typically 0.2 in. w.g. or 50 Pa). Manufacturers publish performance data at multiple static pressure points — ensure the rated flow accounts for the actual duct resistance of the installed system, which should be determined by a duct design calculation.

Commissioning requires flow measurement at the HRV terminals (not the unit spec plate). CSA Standard F326 "Residential Mechanical Ventilation Systems" specifies commissioning and labelling requirements for systems in Canadian homes.

4. Spot Ventilation: Kitchens and Bathrooms

Spot (local exhaust) ventilation removes moisture and pollutants at the source before they disperse through the home. NBC 2020 and ASHRAE 62.2 minimum flow rates for residential spot exhaust:

5. Summer Humidity Control

Health Canada recommends maintaining indoor relative humidity between 30% and 55% year-round. In many Canadian cities, outdoor summer humidity routinely produces indoor conditions above 55% RH without active dehumidification.

Air conditioning with a properly sized refrigerant coil removes latent moisture as a by-product of cooling. The coil must be appropriately sized — oversized equipment short-cycles before adequately dehumidifying. A system sized to Manual J heat load calculations will dehumidify more effectively than an oversized unit.

Standalone dehumidifiers sized to the basement or crawl space area (approximately 30-pint units for spaces up to 1,000 ft²) are the standard approach for basement humidity management in Canadian homes not served by central air conditioning in that zone.

Ultrasonic humidifier producing fine water vapour mist
Ultrasonic humidifiers are efficient but require regular cleaning to prevent bacterial amplification in the water reservoir. Source: Wikimedia Commons (CC)

6. Winter Humidity and Condensation Management

At outdoor temperatures of −20°C (common in Ottawa, Calgary, Winnipeg), the dew point of outdoor air at 80% RH is approximately −22°C. When this air is brought inside and heated to 21°C, its relative humidity drops to approximately 5–8%. Without supplemental humidification, this causes wood shrinkage, static discharge, and mucous membrane irritation.

However, adding humidification to a tight, well-insulated home introduces a condensation risk on cold surfaces. The maximum safe indoor RH in winter depends on outdoor temperature and the thermal performance of the building envelope:

These thresholds assume standard double-pane low-e windows. Triple-pane windows (increasingly common in Canadian new construction) raise the condensation threshold and allow higher indoor winter humidity at the same outdoor temperature.

Whole-home bypass humidifiers connected to the furnace supply plenum add moisture to air in circulation. Drum humidifiers require regular cleaning to prevent Legionella amplification in the water pad. Steam humidifiers (electrode or resistive) are the most hygienic type but consume more energy.

7. Monitoring Indoor Conditions

A combined temperature/humidity datalogger placed in the main living area provides the baseline information needed to assess both summer dehumidification needs and winter humidification limits. Devices that log hourly data over weeks are more useful than spot measurements from a handheld hygrometer.

For CO₂ monitoring as a proxy for overall ventilation adequacy: a well-ventilated residence with normal occupancy should maintain CO₂ below 1,000 ppm (ASHRAE's general guidance level). Concentrations consistently above 1,200–1,500 ppm during occupancy indicate insufficient fresh air delivery relative to occupancy load.

Further Reading