That Energy Blog is published by Kates Energy Modelling Inc.
A heat recovery ventilator (HRV) can be running without delivering the ventilation the home needs. Check three things separately: how much outdoor air it supplies, how much indoor air it exhausts, and whether the controls deliver that service when needed. A fan sound, a wall-control light and an old balancing sticker cannot answer all three.
The same checks apply to an energy recovery ventilator (ERV). Both recover heat; an ERV also transfers moisture between air streams. NRCan explains why supply and exhaust balance matters for performance and house pressure. The installed system still needs to be measured and checked in its actual operating modes.
Start with a complete pair of readings
A practical lesson from ventilation diagnostics is to separate a recorded pressure from a defensible airflow result. Some units use pressure-test ports and a manufacturer’s conversion chart. A pressure in pascals becomes an airflow only through the correct procedure for that model, air stream and operating condition.
If one reading falls outside the chart’s supported range, leave that airflow unresolved. Do not extend the curve by guesswork, borrow the other air stream’s column, or enter zero for a blank cell. Without two valid results, the present supply-to-exhaust balance remains unknown. The next step is to verify the setup and obtain a valid measurement, not declare the ventilator defective.
This is also why a signed commissioning label has a limited job: it records an earlier result. Keep it, compare it with the current test, and investigate differences rather than treating the label as a measurement taken today.
Balanced and sufficient are separate checks
The chart below uses invented round numbers to make the distinction clear. For this example only, assume the ventilation design calls for 100 cubic feet per minute (CFM) on each air stream in the tested mode. That is not a recommended rate for every home.
Three airflow pairs, three different conclusions
Common scale: 0–100 CFM. Teal = supply; brown = exhaust.
| Pair | Supply / exhaust | What it establishes |
|---|---|---|
| A | 100 / 100 CFM | Matches both example flow targets at that test condition. |
| B | 60 / 100 CFM | Exhaust exceeds supply by 40 CFM; find the cause before accepting the setup. |
| C | 60 / 60 CFM | Equal flows, but each is 40% below the example target. |
None of these pairs proves that every bedroom receives enough outdoor air, that the timer runs long enough, or that other exhaust equipment is safely accommodated. Health Canada’s ventilation guidance distinguishes system balance, distribution, operating conditions and pollutant-source control.
Ask for a commissioning record you can use
For a service visit or new installation, ask the contractor to leave the following information. This is a practical documentation checklist, not a substitute for the applicable design, installation instructions or code requirements.
- Equipment and method: test date, model number, measurement method, units, and the relevant manufacturer’s instructions. If pressure ports were used, retain the pressure readings and the chart or conversion reference.
- Target and actual flow: supply and exhaust targets, valid measured results for both, and the acceptance criterion used. Avoid an unexplained “balanced” checkbox.
- Operating state: normal ventilation, boost, timer settings and any required furnace-fan interlock. Record which other equipment was running.
- Condition and settings: filter/core condition, intake and exhaust obstructions, damper or fan settings, and changes made during the visit.
- Distribution and handover: the rooms served, checks at the terminals where needed, and a demonstration of the controls the homeowner will actually use.
NRCan’s HRV homeowner guide covers airflow checks, balancing, controls and maintenance. Follow the specific unit’s manual for cleaning and service. A tissue at a grille can reveal air movement; it does not replace a quantitative airflow measurement.
Where ventilation shares furnace ductwork, check the required interlock rather than assuming a running circulation fan supplies outdoor air. Also check normal and boost operation separately. HVI’s selection and controls guidance identifies airflow, frost protection, controls and fan power as separate considerations.
What this check cannot tell you
An airflow pair does not measure heat-recovery efficiency, annual energy use or bill savings. Certified recovery ratings account for prescribed test conditions and corrections. NRCan’s HRV/ERV technical specifications explain why a temperature rise alone is not the full rated efficiency calculation.
Nor should an HRV be adjusted to conceal a separate air-leakage or odour pathway. Diagnose the pathway, the pressure driver and the ventilation service together. Combustion spillage requires qualified investigation; an HRV is not a remedy for a malfunctioning fuel-burning appliance.
The useful closeout is a record of both valid airflows, the required operating sequence and the criteria met. If a reading remains unresolved, the report should say what must be measured next. That gives the homeowner and the next technician something more dependable than an old checkbox.
Technical sources checked October 13, 2026. General guidance above supplements the equipment manufacturer’s instructions. The worked example is illustrative and is not a code-compliance assessment.