Ventilating a Home Without a Basement: The Mechanical Closet Puzzle in Saint-Henri
Le Sud-Ouest has a type of housing that complicates any ventilation project: units without mechanical space. Converted condos in Griffintown, renovated plexes in Saint-Henri, row houses in Pointe-Saint-Charles with 30-inch crawl spaces, and lofts in former industrial buildings along the Lachine Canal. No usable basement, no mechanical room, and often only one available closet—the laundry or hallway closet.
The project discussed here fell exactly into that category. An upper-floor unit with 9-foot ceilings, drywall throughout, and a 30-inch-wide closet shared with storage shelves as its only technical space. The owner had received two quotes before calling us: one proposed sacrificing an entire wardrobe, while the other suggested doing nothing.
The Problem Behind the Request
The initial call was not about ventilation. It was about the bathroom staying damp for three hours after a shower, the bedroom window frosting over in January, and a persistent odor coming from the neighboring unit through the shared stairwell. Three symptoms, one cause: no mechanical air exchange in a home whose envelope had been rebuilt during the conversion.
Older buildings in Le Sud-Ouest leaked air everywhere, and this unintentional permeability provided a minimum amount of air exchange. Recent renovations—triple-glazed windows, spray foam in the brick walls, and complete caulking—eliminated this mechanism without replacing it. The result can be measured: winter relative humidity above 55%, CO₂ concentrations exceeding 1,500 ppm in a closed bedroom early in the morning, and volatile organic compounds accumulating because nothing removes them.
Why the Fantech HERO 120H Was Right for This Space
The unit was selected based on a physical constraint above all other criteria: the connections had to exit through the top. A unit with side ports requires clearance on both sides, which simply did not exist between the closet wall and the shelves.
The HERO 120H is a top-port air exchanger, allowing it to sit against a wall while the four ducts run directly upward to the plenum above the suspended ceiling. Its actual specifications:
- Airflow range: 53 to 112 CFM at 0.4 in. water column
- Connections: 5 in., round—directly compatible with standard flexible duct
- Dimensions: 24 1/4 in. (H) x 23 1/4 in. (W) x 11 1/2 in. (D)
- Weight: 41 lb
- Power supply: 120 V, 1.2 A max
- Power consumption: 69 W at low speed, 165 W at high speed
- Adjusted sensible recovery efficiency: 85%
- Sensible recovery: 80% at 0 °C, 64% at -25 °C
- Defrost: by recirculation, with a mechanical backdraft damper
This last point matters most in a Montreal home. When the outdoor temperature drops below -5 °C, the moisture contained in stale air begins to freeze in the core. Two strategies are available. Units with supply fan shutdown stop bringing in fresh air for several minutes every hour—during a week at -25 °C, that adds up to hours without ventilation. The HERO's recirculation defrost closes the outdoor-air intake and circulates indoor air through the core to thaw it, without ever interrupting air circulation. In a 900-square-foot home where four people sleep with their doors closed, the difference is noticeable in the morning.
The 11 1/2-inch depth solved the rest: the unit leaves a usable passage in the closet, and the storage shelves were preserved.
How the Project Unfolded
Wall-Bracket Mounting, Not Ceiling Mounting
The unit rests on a steel bracket anchored to the wall structure, with neoprene isolation pads between the cabinet and the bracket. This approach replaces the chain suspension used in basements, which was impossible here because there was only drywall and a low-clearance plenum above.
The wall location is never neutral. We deliberately avoided the shared wall with the primary bedroom. An HRV is not particularly noisy—but in a closed closet directly beside a headboard, the hum of 165 W at high speed becomes a service complaint six months later.
Duct Network in a 10-Inch Plenum
The two outdoor ducts—fresh-air intake and stale-air exhaust—are made of insulated flexible duct with a continuous vapour barrier. This insulation is not optional: an uninsulated fresh-air duct running through a heated space condenses along its entire length, and the water eventually ends up in the drywall. This is the repair we perform most often on existing installations.
The indoor ducts—stale-air return and fresh-air distribution—are aluminized flexible duct, with generous bend radii. Flexible duct bent at a sharp angle in a tight plenum can add the equivalent pressure loss of 20 feet of straight duct, and these invisible losses are what later prevent the system from reaching its intended airflow.
Exterior Penetrations on the Rear Façade
In Le Sud-Ouest, original brick front façades are a sensitive issue, both for the condo board and from an architectural standpoint. We positioned both hoods on the rear façade facing the alley, with more than 6 feet between the intake and exhaust to prevent air short-circuiting.
Three other distances are checked systematically: clearance from the dryer exhaust, clearance from any combustion-appliance vent, and sufficient height above the ground so February snow accumulation does not block the intake. A perfectly balanced unit in October can lose 30% of its intake airflow beneath a snowbank.
Condensate Drain Without a Floor Drain
There was no floor drain in this upper-floor unit. Condensate produced by the core is routed through a flexible tube equipped with a trap to the washing machine's vertical drainpipe. The trap is the detail that sloppy installations overlook: without it, the unit draws air through the drain tube, the balance becomes unstable, and sewer odors can rise into the closet.
Electrical Supply and Control
The unit is powered by 120 V. A dedicated outlet remains best practice: sharing a circuit with a freezer or pump can cause trips that are difficult to diagnose. The low-voltage control wire connects the unit to a wall control installed in the hallway, allowing users to switch between continuous, intermittent, and high-speed modes. For owners who want automatic regulation, the ECO-Touch IAQ control adjusts airflow according to the actual concentration of volatile organic compounds rather than a fixed schedule.
Balancing During Commissioning
The label attached to the unit shows the relationship between airflow in CFM and the measured pressure at the supply and stale-air ports. Balancing is performed at Normal speed with a differential pressure gauge, adjusting the dampers until the two airflows are equal within a 10% tolerance.
An air exchanger that is out of balance does not perform its function: if it exhausts more than it supplies, it depressurizes the home and draws air through the shared hallway, elevator shaft, or neighboring unit—exactly the odor the client wanted to eliminate. If it supplies more than it exhausts, it pushes humid air into the walls.
The Most Common Air Exchanger Mistakes in Multi-Unit Housing
- Installing the unit without ever balancing it. An HRV that is connected and blowing is not necessarily a functional HRV.
- Exhausting air only from the bathroom. Fresh air must enter the bedrooms and living room, where occupants spend their time.
- Placing the unit against a bedroom wall. Structural noise cannot be corrected afterward without moving everything.
- Omitting the condensate drain trap.
- Neglecting maintenance. Rinse or replace filters every three months, wash the core once a year, and clear snow and lint from the exterior hoods. A dirty core loses efficiency and makes the motors work harder.
- Believing that an HRV replaces a range hood. These are two separate systems with two separate functions.
Our Residential Ventilation Practice in Greater Montreal
At AirGreen, we install ventilation systems in Montreal, Laval, Longueuil, the North Shore, and the South Shore, in settings ranging from Griffintown condos to Chomedey bungalows, as well as homes in Brossard and cottages in Terrebonne. Each area brings its own constraints: façade clearances, condo boards, reduced ceiling heights, and shared walls.
Our method does not change from one project to the next. We calculate the required airflow based on the number of rooms before proposing a model. We verify that the selected unit physically fits in the available space, with the service clearances needed to remove the filters and core. We balance the system during commissioning and record the readings. And we show the client how to maintain the unit, because an HRV forgotten for five years becomes nothing more than a metal box attached to a wall.
For an HVAC installation assessment or the addition of an air exchanger in Le Sud-Ouest, Saint-Henri, Pointe-Saint-Charles, Ville-Émard, or elsewhere in Greater Montreal, our team visits the site, takes measurements, and proposes a system sized for the actual home rather than for a catalogue.