Ventilation Retrofits for older buildings - a Smarter Path Forward

In 2023, BC Housing published the results of a study across five social housing buildings in Metro Vancouver to examine why ventilation is failing in older buildings — and why the systems these buildings rely on are no longer adequate. This article picks up where that one left off. If the legacy systems are the problem, what does a workable solution actually look like — and why is replacing equipment not enough to get there?

What makes the BC Housing study particularly useful is not just what it found, but what it tried. All five buildings underwent retrofits during the monitoring period. Windows were replaced. Exhaust fans were upgraded. Building enclosures were improved. Researchers measured conditions before and after.

The result: no measurable improvement in indoor air quality.  Not because the work was poorly done. Because the ventilation strategy itself was never changed. That distinction is the starting point for this article.

The five buildings in the BC Housing study represent a cross-section of older Canadian housing stock. Four are wood-framed low-rise structures. One is an eight-storey concrete tower. All rely exclusively on exhaust-only ventilation — a strategy that assumes fresh air will enter suites passively while stale air is mechanically removed.

Three of the five buildings use corridor pressurization: fresh air is supplied mechanically to shared corridors, with the expectation that it will migrate into individual suites through door undercuts or gaps. The remaining two buildings open directly to the exterior and rely on exhaust fans to draw air in from outside.

In both cases, fresh air delivery is indirect. The system does not supply air to the suite — it creates conditions under which air might find its way there.

This is where the BC Housing study becomes particularly instructive. Four of five buildings received new or upgraded exhaust fans as part of their retrofit packages. Researchers measured exhaust airflow rates before and after. Flow rates improved in some suites. In others they didn't — roughly half of all monitored suites remained below code-minimum airflow rates even after the upgrades.

But the more telling finding wasn't the flow rates. It was what happened to indoor air quality regardless of whether the fans improved or not. CO₂ concentrations — the primary indicator of ventilation effectiveness — showed no significant change across any of the buildings post-retrofit.

The study's explanation is direct: occupants weren't using the fans. Noise was the primary complaint. A fan that stays off because it's too loud is infrastructure that exists on paper only.

This points to something more fundamental than aging equipment. These systems depend on occupant behaviour to function. When that behaviour changes — or never happens consistently in the first place — the system fails. Not because it's broken. Because it was designed around assumptions that don't hold in real buildings.

Corridor pressurization depends on maintaining a consistent positive pressure differential between the corridor and the suite. The BC Housing study measured those differentials directly: less than 3 pascals across all monitored suites — far below what would be needed to drive meaningful airflow through a door undercut into a living space.

The reasons are predictable. Stack effect, wind pressure, open windows, and operating exhaust fans all compete against the mechanical system simultaneously. The pressure environment shifts constantly. Air moves through whatever path offers least resistance — which is rarely the intended one.

When pressure relationships break down, air doesn't simply stop moving. It moves differently. Corridor air — along with whatever it carries — can migrate into living spaces rather than out of them. The BC Housing study documented this directly. Tenants reported tobacco smoke entering non-smoking suites despite efforts to seal around doors. In some cases, running the exhaust fan made the problem worse, drawing corridor air in faster.

Exhaust-only ventilation faces the same underlying issue. The system assumes that fresh air will enter passively to replace what's exhausted. But passive infiltration is not ventilation. It is air leakage — uncontrolled, unfiltered, and unreliable. And critically, it depends on occupants keeping windows open — which they will not do in winter to stay warm, will not do in summer when it's too hot or the air conditioning is running, and are specifically advised not to do during wildfire season when outdoor air quality deteriorates. The window, which functions as the backup ventilation strategy in all five of these buildings, fails in precisely the conditions when reliable fresh air matters most. The consequences extend beyond comfort. Without reliable fresh air exchange, CO₂ accumulates, indoor pollutants concentrate, and moisture generated by normal occupant activity has nowhere to go — conditions that affect both the people living in the building and the building itself.

The BC Housing study's recommendations follow directly from its findings. For future retrofits seeking genuine IEQ improvement, the report identifies suite-level ventilation as the necessary shift — specifically mechanical systems that supply fresh air directly to individual suites rather than relying on corridor pressure or passive infiltration.

The logic is straightforward. If the failure is that fresh air delivery depends on indirect pathways that are inherently unstable, the solution is to make delivery direct. But there is a second dimension to this that matters equally in retrofit contexts: a ventilation system that operates continuously and automatically removes the conditions that drive problematic occupant behaviour in the first place.

In buildings without reliable mechanical ventilation, occupants self-ventilate. They open windows. In winter, that means heated air leaves the building every time a resident decides they need fresh air — which is constantly, because they genuinely need it, and have no other means of getting it. The energy consequences accumulate quietly but significantly across an entire building. Centralized heating systems compensate for uncontrolled air exchange by running harder and longer. The building bleeds energy not through any single dramatic failure, but through the steady, predictable result of a ventilation gap that forces occupants to improvise.

LUNOS closes that gap. When residents have reliable fresh air delivered mechanically, windows stay closed during extreme weather. Exhaust fans return to their intended function — localized moisture control — rather than being pressed into service as the primary means of inducing airflow. Centralized systems stop compensating for uncontrolled infiltration. The result is a building that performs closer to how its asset plan intended — in terms of both indoor air quality and energy use.

LUNOS decentralized HRV systems work on this principle. Paired units installed through the exterior wall alternate between supply and exhaust cycles, recovering heat from outgoing air while delivering filtered fresh air directly into the living space. The system doesn't depend on pressure relationships with adjacent spaces. It doesn't require occupants to activate a fan. It doesn't rely on air finding its way through a door undercut.

Each suite becomes its own ventilation zone. Airflow is balanced within the suite rather than managed at the building level. And because each unit operates independently, cross-contamination between suites is reduced — the system doesn't create the pressure imbalances that drive air through shared pathways.

For retrofit applications, the practical constraints matter as much as the performance logic. LUNOS units install through a 6.25-inch wall penetration with no ductwork, no mechanical room requirements, and minimal electrical demand — operating at 1.4 to 3.3 watts per pair. In occupied buildings where disruption is a primary concern, that installation profile is not incidental. It's what makes the approach feasible.

Is your building still relying on corridor pressure or exhaust fans to deliver fresh air? We can help you find a better path. Get in touch.