Installation of a GREE FreeMatch R32 dual-zone wall-mounted heat pump in Lachine (Old Lachine, Montreal)

In a duplex, the building itself takes precedence over the load calculation

Lachine is one of the first three parishes on the Island of Montreal, founded in 1667 and officially bearing this name since 1676. Two dates shaped its real estate much more than its founding: 1825, the inauguration of the Lachine Canal, and 1847, the arrival of the railway. The industrial corridor that developed between the two—the Dawes Brewery opened in 1826, and factories followed the canal—filled Vieux-Lachine and the streets descending toward Notre-Dame Street with workers' housing, including tightly packed duplexes and triplexes built on narrow, often shared lots. Today, the borough covers 17.7 km², has a long frontage on Lake Saint-Louis, and includes the Lachine-Est sector, which is undergoing extensive redevelopment.

This context is not decorative. On a multi-zone wall-mounted heat pump installation in a duplex, the constraints that determine the project are not thermal; they are legal, geometric, and related to shared walls. The load calculation comes afterward, and that is what this article documents.

The project and the selected unit

Apartment in a Vieux-Lachine duplex, with the electric baseboards retained and no ductwork. Two zones: a living area extending toward the front and a primary bedroom at the back, separated by a hallway and a door—the exact configuration visible in the photo, where the head is mounted very high on the section of wall next to a door frame.

Selected configuration: 12,000 BTU/h in the living area and 6,000 BTU/h in the bedroom, for a total of 18,000 BTU/h installed on a 24,000 BTU/h GWHD(24)ND6MO compressor—a ratio of 75%, the lowest we have published. Below, we explain why the compressor is larger than the load and why this is not an error.

Technical specifications for the installed outdoor unit

Where does the outdoor unit go when you do not have your own yard?

On a single-family property, you choose the outdoor location. On a narrow-street plex, you negotiate among four options, and none is neutral:

1. The backyard, when one exists and is not a common part of the building. It is technically the best option—drained ground-mounted base, easy service access—and often the most complicated administratively.
2. The rear balcony, with the exterior staircase right beside it. A freestanding base placed on a wooden structure is not the same as a ground-mounted base: the actual load-bearing capacity must be checked, and a 51 kg appliance plus snow plus defrost water end up on a deck that was never designed for this.
3. Wall brackets on the rear or side wall, covered in detail in our Ahuntsic-Cartierville guide regarding anchoring and vibration. On a plex, they add a specific question: the wall supports the neighbour's unit as much as yours.
4. The flat roof, very common on Montreal plexes, and almost always the worst idea without a study—punctured waterproofing, a point load on a structure you cannot see, service access by ladder, and above all the model's 15 m height difference limit, along with the question of who owns the roof.

Our method is consistent: the location is determined during the technical visit, before the order is placed, with a sketch and photo provided to the customer. In a plex, this sketch also helps you discuss the matter with the neighbour, condo association, or owner—and it is better to have it before the work than afterward.

The piping often passes through areas that are not yours

This is the detail nobody anticipates. In a single-family home, a refrigerant line stays on your property from start to finish. In a plex, a route between a ground-level outdoor unit and a second-floor indoor head almost necessarily passes through a shared wall, a floor cavity, a stairwell, or a façade—in other words, through parts of the building that are not necessarily private portions.

Three practical consequences:

• A façade penetration is a modification to the building envelope. In a co-owned building, the façade is almost always a common portion, even below a window that belongs to your unit.
• An exterior conduit cover is visible. The routing, colour, and alignment of the conduit covers become a collective appearance issue, not merely a finishing detail. We align the downspouts with the building's existing lines and submit the routing in advance.
• A shared floor void requires the same rigour as a load-bearing wall. Continuous insulation along both lines, even in a heated area; the drain slope checked before fastening the plate; and the firestop restored if there is a fire separation between units. We have developed these points in our reports on Saint-Étienne-de-Beauharnois and Saint-Urbain-Premier.

Divided co-ownership, undivided co-ownership, or rental property: three different files

We are neither notaries nor lawyers, and we encourage every client to read their own deed. But after dozens of plexes, we can say what holds up a project:

• In divided co-ownership, the declaration of co-ownership determines what is a common portion, a common portion for restricted use, and a private portion. A rear balcony is very often a common portion for restricted use: you have the right to use it, but you do not own it. Written authorization from the syndicate should be requested before ordering the equipment, not the day before installation.
• In undivided co-ownership, a common arrangement in Montréal plexes, there is no syndicate, but rather an undivided co-ownership agreement and co-owners who jointly own the entire property. The agreement is made between the individuals, and it is worth putting in writing—including who pays for maintenance and who keeps the equipment if one of the co-owners sells.
• In a rental property, the question becomes: who buys it, who installs it, who maintains it, and who owns the equipment at the end of the lease. A wall-mounted heat pump is not a window air conditioner that you take away in a box. A tenant who finances a system attached to the building should set this out in writing; a landlord who installs one should also understand that it increases the rental value of the property.

Finally, zoning regulations are the responsibility of the borough: placement of mechanical equipment in the yard, setbacks, visibility from the street, and noise at the property line. We do not publish any numerical values: these rules vary from one borough to another and should be verified directly with Lachine. The mechanism by which noise is attenuated with distance is explained in our Huntingdon report.

One meter, two dwellings: who pays for the equipment that runs

A point rarely raised, yet decisive in a plex. The indoor units of a FreeMatch are powered by the outdoor unit, so the entire system draws from a single circuit, connected to a single panel. If that panel belongs to the downstairs dwelling while the heads serve the upstairs one, the heat pump’s electricity bill is paid by the wrong occupant for fifteen years.

On this project, the circuit was run from the panel serving the dwelling, and the circuit number is recorded in the handover file. When the panel for the correct dwelling has no room left, the issue becomes electrical rather than mechanical, and it falls to a master electrician.

Why use a 24,000-BTU unit for only 18,000 BTU/h installed

The 75% ratio is the lowest in our entire series, and it has nothing to do with the heat load. The compressor was chosen for the distance, exactly as we had done in Verchères on a four-head project.

In a plex, the outdoor unit is downstairs and at the back; the heads are upstairs and on either side of the dwelling. The two actual line runs, including bends, added up to considerably more than the 10 m of factory charge and came close to the 40 m total line length allowed by the 18,000-BTU/h model. The GWHD(24)ND6MO provides 30 m of factory charge and 60 m total: clearance is no longer an issue, and the weighed additional charge remains modest.

Two honest notes for balance:

• A compressor larger than the load is not free. It costs more, weighs 51 kg instead of 35.5, and its EER2 of 12 is slightly lower than the 12.5 of the 18,000-BTU model.
• The system’s modulation floor is 7,500 BTU/h, so it is above the capacity of the 6,000-BTU/h head alone. The bedroom operates with the setpoint maintained rather than starting up late, and the baseboard heaters remain in service. The mechanism is detailed in our Saint-Chrysostome case study.

Having one installed in February: what really changes in the off-season

The second distinctive feature of this project is the timing. A large share of ductless heat pump requests comes in between May and August, creating a backlog at the worst possible time and leaving the cold months strangely quiet. The question we’re always asked then is the same: can you install a heat pump in winter?

Yes. But you need to know what changes—and what a serious contractor does differently.

What cold weather changes about vacuum evacuation

The vacuum evacuation is the operation that determines a compressor's longevity, because a hermetic compressor dies from contamination introduced on the day of installation—we discussed this in our Saint-Louis-de-Gonzague case study.

In cold weather, residual moisture in the piping evaporates much more slowly: it may even remain as ice while a pressure gauge displays what appears to be a proper vacuum. The consequence is simple and non-negotiable: we do not shorten the evacuation time in winter; we extend it, and the 500-micron rise test becomes even more important than the vacuum level reached. A contractor who tells you the vacuum time is the same in January as in July does not understand what they are measuring.

Commissioning takes place in two stages

This is the point we put in writing in every winter quote. In February, we verify the heating under the real conditions in which it operates—it is the best time of year to do so, and it is an advantage that a summer installation does not have.

Cooling, on the other hand, cannot be meaningfully validated at -10 °C. The unit will start, but all the readings taken—pressures, temperature differences, and expansion-valve behavior—are so far from the design conditions that they prove nothing about July comfort. We therefore schedule a verification visit in the spring, included in the contract and specified in writing, when the outdoor temperature allows for a meaningful test.

“-30 to 48 °C in cooling mode”: what this range really means

The GWHD(24)ND6MO specification sheet states operation in cooling mode from -30 to 48 °C. That is accurate, and it is regularly misread.

This low temperature range is not intended for your living room: it exists for spaces with a year-round cooling load—server rooms, telecommunications rooms, technical equipment areas—where heat must be removed even when it is freezing outside. In a residence, it is a feature with no practical use. It does not mean that the air conditioner should be adjusted in winter, nor that a cooling test in January replaces a cooling test in June.

Frozen ground, snow, and the outdoor base

Three physical constraints that winter imposes on outdoor installation:

• A draining stone bed cannot be prepared in frozen ground. Depending on the situation, we install on wall brackets—which is often the right permanent choice for a plex anyway—or we lay a properly cleared temporary base, with a correction planned for the spring thaw, written into the contract and not left to anyone's memory.
• Snow hides the slope of the land. Where the defrost water will flow in spring cannot be determined under 40 cm of snow. We check the slope and drainage before securing anything, and direct the drainage away from the foundation.
• The base height is chosen based on the year's snowfall, not the snow on the ground that day. A unit installed low in January, when the snowbank is already there, will be even lower than necessary the following winter.

What you gain by booking off-season

Without promising discounts, four concrete and verifiable benefits:

1. Short lead times. A February request can be scheduled in days; a July request takes weeks to schedule.
2. A pressure-free technical visit. The outdoor unit's location, approval from the condo association or owner, the line-set routing, and the electrical circuit can all be sorted out before the work begins — which, in a plex, is exactly where projects go off track.
3. Heating tested under real-world conditions.
4. The unit is ready for the first heat wave rather than ordered during it.

Clearance above the cabinet

A word about what the photo shows: the indoor unit is mounted very close to the ceiling. The clearances required around a wall-mounted cabinet, and the thermal reasons for respecting them, are explained in our guides to Verchères and Napierville, and the manual supplied with the unit is authoritative.

One mechanical detail that is easy to overlook and has nothing to do with heating or cooling: the front panel must be able to swing open. That is how the filters are removed, and on many models the panel lifts upward. A cabinet mounted tight against the ceiling may meet the required intake clearance on paper and still make rinsing the filters a chore — difficult maintenance is maintenance that does not get done. Mounting height must be checked with the panel open, during installation, not measured from a plan.

Mistakes to avoid in a plex

• Order the unit before obtaining written authorization from the condo association, co-owners, or owner.
• Treat the rear balcony like a concrete slab. Its load-bearing capacity must be verified.
• Drill through a façade assuming it is private because the window is.
• Connect the system to the wrong unit's electrical panel.
• Choose the compressor based on load alone when the runs are long. In a plex, distance is the deciding factor.
• Secure a base to the ground on frozen soil without a planned adjustment for thawing.
• Accept a cooling test in January as a complete commissioning.
• Mount the head so high that the front panel can no longer be opened comfortably.

Commissioning, rebates, and warranty

Standard protocol: an extended deep vacuum during the cold season, with a rise test below 500 microns; weighed additional charge at 20 g/m beyond the 30 m factory charge, recorded in the file; functional testing of one head at a time; readings at each port; a drain test for each pan before closing everything up; a written note of the balance point; and a spring visit to verify cooling mode for a winter installation. Serial numbers associated with their respective components, installed lengths, circuit number and original panel, and the AHRI number 214931587 for the installed combination are provided to the occupants.

Because the dwelling is heated with electricity, Chauffez vert does not apply—this program is intended for converting from fossil fuels. Hydro-Québec’s LogisVert and Rénoclimat are the avenues to examine; in a multi-unit building, the question of whose name the file is opened under must be settled before the work, not afterward. The declared AHRI number must match the installed combination exactly. The criteria change over time: we validate them when the file is opened rather than publishing outdated amounts.

The warranty is 10 years, extended to 12 years with registration through the distributor and proof of installation; we complete the registration with the customer at the end of the project.

We install throughout Greater Montréal

At AirGreen, we design, install, and maintain HVAC systems in Montréal—Lachine, the Southwest, and the entire island—as well as in Laval, Longueuil, on the North Shore, and on the South Shore. As a licensed, insured RBQ contractor, we document our work: location sketches provided before the work begins, piping lengths recorded in the file, port assignments, the panel and circuit noted, and a written list of what the unit will and will not do.

A multi-unit building adds stakeholders to a project, not insurmountable difficulties—as long as you consult them before drilling. Ask us for an on-site assessment for your wall-mounted heat pump, your wall-mounted air conditioner, or your HVAC maintenance: during the off-season, we have time to do things in the right order.