An address reached by bridge: distance as a design consideration
This project in L'Île-Bizard–Sainte-Geneviève takes us to the least densely populated borough on the Island of Montreal, and to an installation configuration we encounter often but have never addressed on its own: the indoor unit installed in a corner of the room.
The debate over the model has taken place elsewhere, and we will not repeat it here. We have published the five possible reasons for choosing one or the other of the two units that accept two heads—the third port and heating reserve for a project in Beaconsfield, reading the “min. – max.” line for a project in Dorval, the rule that a single head can never equal the compressor for a project in Kirkland, the run length imposed by a roof for a project in Dollard-des-Ormeaux, and the distinction between precharge and hard limit for a project in Côte-des-Neiges–Notre-Dame-de-Grâce. What follows concerns something else: what the geographic location and the room’s geometry do to an HVAC installation.
The context: 780 inhabitants per square kilometre
L'Île-Bizard–Sainte-Geneviève has approximately 18,400 residents spread across 23.6 km², or 780 inhabitants per square kilometre. The figure is worth putting into perspective: it is nearly eleven times less dense than Côte-des-Neiges–Notre-Dame-de-Grâce and seven times less dense than Ahuntsic-Cartierville, two boroughs where we have documented recent projects. The average age is 44.
The borough brings together two areas separated by the Rivière des Prairies: L'Île-Bizard proper, a residential area bordered by Lake of Two Mountains, and Sainte-Geneviève, a heritage village stretching along Gouin Boulevard. It has six parks, one nature park—the Bois-de-L'Île-Bizard, part of the Grand Parc de l'Ouest—and three golf courses, as well as Cégep Gérald-Godin and the Pauline-Julien performance hall.
For a heat pump project, this low density reverses several of the instincts we apply everywhere else on the island. The neighbour is not three metres away. The sound constraint, which determines the placement of the outdoor unit in a dense area, loses almost all its force here: we published the complete reading of decibel levels and municipal installation regulations for a Huntingdon job, and on this property the matter was settled in a single sentence. What replaces it is distance.
Two zones, 12,000 + 6,000 BTU/h
The open ground floor received 12,000 BTU/h and a closed room upstairs 6,000 BTU/h, for a total of 18,000 BTU/h of installed indoor capacity on a GWHD(24)ND6MO rated at 24,000 BTU/h — a ratio of 75%, the most conservative we have published for this compressor.
| Data that supports the argument | GWHD(24)ND6MO |
|---|---|
| Connectable indoor units | 2 to 3 |
| Modulated range, cooling and heating | 7,500–31,400 BTU/h |
| SEER2 / HSPF2 / EER2 | 21 / 10 / 12 |
| EER / COP | 3.80 / 3.9 W/W |
| MCA / maximum protection | 19.5 A / 25 A |
| Factory R32 charge | 1 700 g |
| Precharge / total length / elevation difference | 30 m / 60 m / 15 m |
| Sound level (high speed) | 58 dB(A) |
| Weight | 51 kg |
| AHRI codes (ductless / ducted / mixed) | 214931587 / 593 / 597 |
At 75%, neither indoor unit is ever served second, even when both zones call at the same time — an ordinary, not hypothetical, situation when there are only two zones. In return, the system's modulation floor, 2,200 W or approximately 7,500 BTU/h, exceeds the capacity of the small 6,000 BTU/h head: this zone operates in short cycles when it is the only one calling for heat. The mechanism is explained in detail in our Saint-Chrysostome article, and the electric baseboards remain in service, set 2 to 3°C below the heads' setpoints.
The Jacques-Bizard Bridge, and what a round trip really costs
The L'Île-Bizard area is connected to Sainte-Geneviève by the Jacques-Bizard Bridge, which crosses the Rivière des Prairies. The original structure dated from 1892–1893; a new four-lane bridge, rather than three lanes, was put into service in November 2024.
This detail may seem insignificant on a wall-mounted heat pump estimate. Yet it determines how the job is organized.
A forgotten fitting, a non-compliant part, a missing adapter: everywhere else, it's twenty minutes. Here, it's crossing a bridge, a round trip, and a crew tied up while the job waits.
For a project in Saint-Lazare, we published how access time—in that case, setting up a rolling scaffold in a double-height hall—is calculated and included in a quote rather than hidden in a total. The logic is identical here, but the variable is not height; it is geography. A contractor who bills an island address exactly like a Ville-Marie address has not looked at the map, and it always shows in the end: either in the price or in the number of visits.
What we are changing in the method
Three decisions made before the truck leaves:
- The truck leaves fully equipped. Flaring tools, a dry nitrogen cylinder, a vacuum pump, and a micron gauge go to every job site, without exception. The method itself—flaring, nitrogen pressure testing, deep vacuum with rise testing, and weighed-in charge—was published in detail for a project in Côte Saint-Luc; what is specific to an island address is that we cannot afford to improvise when a part is missing.
- The preparation checklist goes out before we do. A 2 m clearance at each indoor unit location, access to the electrical panel, parking near the condenser location, and pets kept away while the doors remain open. Losing half a day to move a piece of furniture is not the same half-day depending on the distance between the job site and the workshop.
- Installation and commissioning in a single mobilization, whenever the project allows it. On some projects—one section still under construction, a finish still to be completed—the two visits remain necessary; in that case, we announce it in the quote from the outset rather than presenting it as an unforeseen issue.
Maintenance scheduled outside peak periods
The most useful point for a local homeowner, and the one we include in the contract: the annual HVAC maintenance visit should be scheduled in May or September, not July.
The reason is prosaic. In the middle of a heat wave, service response times grow longer everywhere, and they grow even longer when a bridge must be crossed to get there. A system maintained in the spring gets through the summer without a service call; a system whose filter turns out to be clogged on July 3 has to wait. Parts availability follows the same logic: for a project in Saint-Louis-de-Gonzague, we explained why the question to ask is not “how many years of warranty” but “who keeps the part in stock in Quebec.”
The owner is the first line of maintenance
For two units, routine maintenance involves very little: two filters rinsed every 4 to 8 weeks during intensive use, two pans and two drains checked, and an outdoor coil rinsed once a year. None of these tasks requires a technician.
We therefore do not treat end-of-project training as a mere courtesy. During commissioning, we physically open the front panel in front of the client, remove and reinstall each filter, and leave a one-page sheet for each room. At a property reached by bridge, a filter the owner knows how to rinse is better than a service call they will have to wait for.
A corner-mounted unit: the geometry that almost nobody adjusts
The photo from this project shows the indoor unit mounted high, very close to the corner formed by two walls. This is a common installation, often the only possible one, and it changes two things in opposite directions.
The corner increases reach and degrades measurement
A wall-mounted air conditioner projects its air along the ceiling before it falls toward the back of the room. From a corner, this jet travels diagonally, along the room's greatest dimension. This is a real advantage that few people put into words: at equal capacity, a corner-mounted unit reaches farther than one installed in the middle of a long wall. The behavior of the jet itself—Coandă effect and ceiling obstacles—was covered for a Sainte-Martine project.
The drawback is exactly symmetrical, and it concerns the measurement. The unit draws its return air from above, at the top of the corner—the room's deadest point, where air stagnates the most, heat accumulates in winter, and air circulation is weakest in every season. A unit in a corner therefore reads air that is less representative than usual of what the occupants breathe.
Three corrections applied during commissioning
- Minimum fan speed increased by one setting in this zone, so the corner does not stagnate.
- Control based on the sensor of a wall controller installed on a clear interior wall rather than on the unit's return-air sensor, when the supplied configuration allows it. We covered the wall controller, its sensor, and its pitfalls for a Kirkland project, as well as the question of the return-air sensor read at 2.1 m for a Saint-Amable project.
- Stable setpoint, because a unit that reads stratified air and is subjected to three-degree jumps produces exactly the abrupt starts people complain about afterward.
Vertical deflectors, adjusted only once over the life of the unit
Here is the setting we have never discussed in some forty articles, and which matters more than all the others for a corner installation.
A wall-mounted unit has two types of louvers. The horizontal louver—the one you can see, which moves up and down and is controlled by the remote—directs air upward or downward. This is the one everyone knows, and we have published the counterintuitive rule more than once: louvers forward in cooling mode, downward in heating mode.
The vertical deflectors, meanwhile, are located behind the horizontal louver. They direct air to the left or right. On most models, they are adjusted by hand, never with the remote control, and you need to know they exist to go looking for them.
The direct consequence is that they are adjusted once, during installation—often left in the center, just as they came from the factory—and never touched again for fifteen years.
On a unit installed in the middle of a wall, this is not a major issue. On a corner unit, it is decisive. Deflectors left in the center send air toward the opposite corner or, worse, against the adjacent wall a few centimeters away: the jet is redirected toward the intake grille, the unit recirculates its own treated air, thinks the job is done, and the room does not. Oriented to sweep across the room's useful diagonal, the same deflectors completely transform the result without changing a single electronic setting.
Permanent swing mode is not the solution
The usual objection is to leave swing mode permanently enabled and consider the problem solved. Three reasons why we do not recommend this by default:
- Swing affects the horizontal louver, not the vertical deflectors. It therefore does nothing at all to correct the directional flaw of a corner installation.
- In a small enclosed room, a continuously sweeping jet is perceived as an intermittent draft rather than comfort, and this is a frequent complaint in bedrooms.
- In heating mode, swing periodically sends warm air upward, which goes exactly against the goal—pushing heat toward the floor, where the occupants are.
Our practice: vertical deflectors adjusted manually during commissioning, their position recorded in the file, the horizontal louver fixed according to the season, and swing reserved for large open rooms and periods when bringing the temperature up.
Mistakes to avoid with a corner installation
- Placing the head tight against the adjacent wall to save a few centimeters. The clearances in the manual for the unit actually delivered govern, and they are not identical on both sides—the issue was addressed for a Beaconsfield project.
- Leaving the vertical louvers in their factory position.
- Setting the zone based on the return-air sensor when that sensor is located at the room's most stagnant point.
- Compensating for poor orientation with a lower setting in summer or a higher setting in winter. This uses more energy and fixes nothing.
- Removing the electric baseboards after a first winter deemed successful.
- Waiting until July to schedule annual maintenance, particularly at this address.
Rebates, warranty, and maintenance
The system provides access to the residential energy-efficiency programs applicable in Québec, notably Hydro-Québec's LogisVert and Rénoclimat. Chauffez vert does not apply here because the home is already heated with electricity. The criteria and amounts change, and we verify eligibility when opening the file rather than quoting a figure in the estimate. The declared AHRI code must match the combination actually installed, otherwise an application may be refused for a purely administrative reason.
The warranty is 10 years, extended to 12 years when the product is registered with proof of installation through the distributor. We complete the registration at the end of the project rather than leaving it to the customer.
AirGreen in L'Île-Bizard–Sainte-Geneviève and Greater Montréal
At AirGreen, we design, install, and maintain multi-zone wall-mounted heat pump systems in Montréal, Laval, Longueuil, on the North Shore, and on the South Shore. In L'Île-Bizard–Sainte-Geneviève, between Gouin Boulevard, Bois-de-L'Île-Bizard, and the shores of Lake of Two Mountains, properties are spacious, neighbors are far away, and outdoor installation constraints are unusually flexible—but every visit comes with a distance cost, shifting the focus to preparation and commissioning quality.
A successful HVAC installation is judged less by the day it is installed than by how many times it has been necessary to come back.