Installation of a GREE FreeMatch R32 two-zone wall-mounted heat pump (GWHD(18)ND6MO) in Montreal’s Le Sud-Ouest borough

In a Southwest row house, the largest wall of the house is the one you are not allowed to use

The approximately forty GREE FreeMatch R32 projects we documented this year took place in detached suburban homes, farms in the Montérégie, a community building, a condo tower, and, most recently, on a flat roof in the West Island. The Southwest requires something else: a dense, old row-house setting where two of the home's four walls belong to you only halfway.

This is a constraint we encounter in Saint-Henri, Pointe-Saint-Charles, Little Burgundy, and the streets of Émard and Saint-Paul, and it completely changes the order of decisions in an HVAC installation. In a detached house, you choose where to place the heads and then find a route. Here, you first establish what is prohibited, and what remains dictates everything else.

At AirGreen, we install HVAC systems throughout Montreal, Laval, Longueuil, the North Shore, and the South Shore. Here is how we approached this two-zone project, and why the job-site photo shows a ladder in a stairwell.

The Southwest project at a glance

The Southwest borough has 94,541 residents across 15.7 km², or approximately 4,984 inhabitants per square kilometre, with an average age of 36. It encompasses five neighbourhoods—Pointe-Saint-Charles, Little Burgundy, Saint-Henri, Émard and Saint-Paul, and Griffintown—and its long-industrial territory has undergone a profound transformation since the reopening of the Lachine Canal in 2002. It has 120 parks and green spaces, seven metro stations, and Atwater Market.

This density is the project's technical starting point. It is lower than that of Côte-des-Neiges–Notre-Dame-de-Grâce, where we recently installed a system at the back of a property, but the built environment is completely different: here, a large share of the housing stock consists of workers' row houses, attached on one or both sides, with a narrow backyard and an alley behind.

Selected configuration:

• Outdoor unit: GREE FreeMatch R32 GWHD(18)ND6MO
• Head 1: 9,000 BTU/h wall-mounted unit, in the ground-floor living area
• Head 2: 9,000 BTU/h wall-mounted unit, at the top of the stairwell, serving the upper floor
• Installed indoor capacity: 18,000 BTU/h, or 100% of the nominal capacity
• AHRI codes: 214931586 (ductless), 214931591 (ducted), 214931592 (mixed)
• Developed lengths: approximately 7 m and 13 m, for a total of 20 m

Two heads of identical capacity, at exactly 100%: we published the two-zone sizing rationale in our Ahuntsic-Cartierville and Vaudreuil-sur-le-Lac articles, and we will not repeat it here. What makes this article is the building.

What a party wall is, and why we do not touch it

Let's first clarify what we are talking about, because the term can be confusing. We recently published a project in Côte-des-Neiges–Notre-Dame-de-Grâce where the condenser had been installed against a shared fence at the back of the yard: a fence, however shared it may be, is not a structural element. This is something else.

A party wall is a wall shared by two adjoining buildings, and it supports the structure of both. Under Quebec law, it is presumed to belong to both owners, and neither may unilaterally carry out work on it that compromises the wall itself or the use the neighbor makes of it. We are not lawyers and do not provide legal advice: when a client wants to explore what their particular situation permits, we refer them to their notary. But in practice, on an HVAC job, our rule is simple and non-negotiable: the party wall receives no drilling, anchoring, or equipment.

Three distinct reasons, and not all of them are legal.

The noise travels to the other side, and it never stops

That is the most concrete and most underestimated reason. A solid masonry party wall is an excellent conductor of low-frequency vibrations—we described the same mechanism in a concrete foundation in our Vaudreuil-sur-le-Lac article.

Mount a wall head on a party wall and you install a permanent source of vibration in direct contact with the structure of the neighboring home. The tangential fan, the expansion valve's clicking, and the casing's expansion: none of this is loud in the room where the unit is located, but all of it becomes audible on the other side, at night, in a bedroom. The complaint rarely comes during the first week. It comes during the first heat wave, is difficult to measure, and can only be resolved by moving the unit.

We prefer to address this issue during the technical assessment, using the neighbor's floor plan when it can be obtained, rather than in the first formal notice.

No outdoor unit on a party wall

The previous reasoning applies even more strongly to the condenser, which weighs 35.5 kg on this model, runs year-round, and defrosts in winter.

We documented wall mounting in our Ahuntsic-Cartierville article, where it was the right solution for a side façade of the client's home. On a party wall, the same solution is ruled out: the anchor passes through a shared structure, vibration is transmitted directly into the neighbour's home, defrost water falls onto property that does not belong to the client, and even routine annual maintenance requires access to a unit suspended above land that does not belong to it.

A solid brick wall has no cavity

There is also a purely structural reason, and it applies equally to the façade walls of an older Southwest building. Solid masonry offers no cavity through which to run refrigerant lines and a drain. There is nothing to open and nothing to close again: the piping either runs in exposed trunking or it cannot run. We addressed anchoring to exposed interior masonry in our Sainte-Clotilde article, and interior trunking and its condensation pitfalls in our Saint-Louis-de-Gonzague article; both apply here exactly as written.

What remains: the rear, and nothing else

Once the party walls are ruled out, a row house in the Southwest has only two exterior walls left: the street-facing façade and the rear façade.

The street-facing façade is, in practice, unusable. It is usually made of original brick, sometimes supports an exterior staircase, is visible to everyone, and installing a unit on a front façade is subject to municipal regulations—which we systematically advise checking with the borough, as we explained in our Huntingdon article and in the section of our website devoted to municipal regulations.

That leaves the rear: the yard, often narrow and deep, and the lane. This is where the outdoor unit was installed, and it requires four checks that we carry out before proposing anything.

1. The actual clearance, season by season. A backyard in the Southwest is bounded by fences and neighbouring buildings. The unit draws air in from the rear and sides and discharges it from the front; the mechanics of air recirculation in a confined space are discussed in our Ahuntsic-Cartierville article and in our Côte-des-Neiges–Notre-Dame-de-Grâce article.
2. Where the defrost water falls. In a narrow yard, the available surface is also the path used to take out the garbage in February. Defrost water that freezes on this path is a fall hazard, not a stain. Our Cèdres article addresses the discharge point and the most common bad idea associated with it.
3. Access from the lane. This is where the equipment, tools and, later, the technician enter. An access route that requires carrying a condenser through the home is not an access route.
4. The distance from neighboring windows. At nearly 5,000 inhabitants per square kilometer, the closest bedroom window is not the client's. This model's 54 dB(A)—the quietest in the range—really helps, but how to interpret a published sound level without a measurement distance is explained in our Huntingdon article.

A few specification-sheet lines, and no more

The GWHD(18)ND6MO was examined in depth in our recent articles: the comparison with the higher-end model in Beaconsfield, the 10 m precharge and additional-charge arithmetic in Ahuntsic-Cartierville, the distinction between the precharged length and maximum total length in Côte-des-Neiges–Notre-Dame-de-Grâce, and the modulation floor in Côte Saint-Luc. We will not revisit them here. The following is all that was used here.

Two figures deserve emphasis in this specific context. The 35.5 kg and the 822 × 550 × 352 mm footprint are what make the unit compatible with a narrow backyard in the Southwest, where a 79 kg model with a depth of 43 cm simply would not fit. And the 20 m of developed length uses half of the maximum total length of 40 m: that is comfortable, but on this model the margin disappears quickly as soon as a route has to go around an obstacle.

Electrical circuit load calculations are the responsibility of a master electrician; our contribution is the manufacturer's data, and we developed the selection logic based on maximum protection in our Saint-Édouard and Napierville articles.

The stairwell: the only large free surface in the house

This is how we arrive at the photo of this worksite. The party walls are ruled out, as is the front façade; the ground-floor walls are occupied by windows, the kitchen, and furniture—and in almost every two-story row house, one large free vertical surface remains: the stairwell wall.

It is both an obvious and demanding location, and it is worth explaining both aspects.

Why the head ends up there

Three reasons come together, and only one of them is an advantage.

• It is the only wall large enough. In a stairwell, no window, piece of furniture, or cupboard competes for the strip beneath the ceiling.
• It is the volume that communicates with the entire floor. A head placed there serves the bedrooms through the open doors. That is also its limitation, and we return to it below.
• Stratification is greatest there. An open staircase has a marked vertical temperature difference between the bottom and the top, which has direct consequences for what the appliance believes it is measuring; the complete mechanism is explained in our Saint-Amable article, and it governs this zone's settings.

The ladder determines the head's position

In the photo, the ladder is set up beneath the appliance, in the stairwell. This detail, which may seem insignificant, is actually what determined the head's exact position, and it is a point we have never had the opportunity to put in writing.

A ladder cannot be placed on steps. It requires a flat, level surface capable of supporting all four feet. In a stairwell, this surface exists in only one place: the landing. This leads to a rule we now apply systematically, extending what we wrote in Saint-Lazare about service access as a sizing criterion: in a staircase, the head's position is bounded by the footprint where a ladder can actually stand.

Specifically, during the technical assessment:

• We set up the ladder the team will actually use before choosing the mounting point—not an imaginary ladder on a plan.
• We check that the person standing on it can reach the front panel and interior filters, not just the casing. An appliance that can be installed but not maintained is an appliance that will not be maintained.
• We check the clearance from the handrail and guardrail, which reduce the usable footprint far more than one might think.
• And when the landing does not allow for anything safe, the answer is not to improvise a support on a step: it is a platform or scaffolding suited to the staircase, included in the estimate. Fall-protection measures required in Quebec beyond a certain working height apply, and they must be planned before the work begins.

The commercial point that follows from this, we will state plainly: a head in a stairwell cannot be installed for the same price as a head in a bedroom. Access, setup, and dismantling take time, and that time exists whether we bill for it or conceal it in a total.

Cardboard against the wall: working in a finished, occupied home

The other visible detail in the photo is a piece of cardboard slipped between the top of the ladder and the wall, just below the appliance. This is not improvisation; it is a method.

We described elsewhere — in our Beauharnois article — how to protect a new appliance from a dusty construction site. Here, the protection works the other way around: the house itself must be protected from the installers. A home in the Southwest is often finished, occupied, and cramped, and a two-zone HVAC installation takes a full day there, amid the occupants' belongings.

What we put in place, and what a customer is entitled to expect from any contractor:

• Protecting contact points. The leg of a ladder leaning against a painted wall can leave a mark within minutes; cardboard or soft padding prevents it. The same principle applies to the ladder feet on a hardwood floor and to the handrail.
• Containing dust during drilling. Drill with a vacuum, use a drop cloth, and do not simply sweep at the end.
• A clear, pre-agreed path between the front door or alley and the work area, with floor protection along the entire route.
• Cleaning up before leaving, not leaving it to the customer.
• And one rule that prevents half the unpleasant discussions: paint touch-ups are not part of the HVAC scope of work, which we write into the quote rather than debate at the end. Our Saint-Bernard-de-Lacolle article explains this scope issue in detail.

Moving equipment up a Montreal staircase

An interior staircase in an old row house is narrow, turns, and has a descending ceiling. Everything must pass through it: the indoor unit and its packaging, the ladder, the tools, the nitrogen cylinder, the vacuum pump, and later the technician with their case.

We take three measurements, and they are determined before the workday:

• Measuring the access route just as carefully as measuring the layouts: width, turn, and clear height beneath the stringer of the upper staircase.
• Unpacking in the right place. An unboxed head unit is easier to carry upstairs than a box, but it is also carried without protection; that is a decision to make on-site, not in the truck.
• Two people on a staircase, always, and never an appliance carried by one person alone, walking backward on the steps.

These are obvious points to anyone in the trade. They almost never appear in a quote, and that is precisely why they cause delays and damage for competitors.

A stairwell is not a room

Here is the limitation that must be stated before signing, because it determines customer satisfaction far more than the choice of model.

A staircase is a transit space. No one stays there, no one has a preferred temperature there, and the setpoint adjusted there corresponds to no one's comfort. We had formulated the principle in our Saint-Lazare article, where one head served a double-height hall.

With a system featuring two heads, the consequence is more significant than elsewhere: dedicating one of your only two zones to a circulation space makes sense only if that head genuinely serves the rooms on the floor. And that requires a concrete commitment from the occupants, which we state explicitly in the end-of-job document:

• Bedroom doors remain open so the floor can be served. A closed door negates most of the effect; we demonstrated this in our Saint-Cyprien-de-Napierville and Baie-D'Urfé articles.
• The airflow is directed toward the floor, not into the stairwell void. The horizontal louver angle is adjusted according to the season—forward in cooling mode, downward in heating mode, the opposite of what intuition suggests—but in a stairwell, it is mainly the vertical deflectors, adjusted by hand behind the louver and then forgotten for fifteen years in most installations, that determine whether the air moves toward the bedroom hallway or into the void. We devoted an entire section to this adjustment in our L'Île-Bizard–Sainte-Geneviève article; it matters even more here, and its position is recorded in the file.
• The minimum fan speed is raised by one level in this area during commissioning, because a head that has to push air into neighboring rooms cannot run at low speed like a bedroom head.
• The return-air sensor is even more misleading here than elsewhere. It is located on top of the appliance, in the warmest air layer of a highly stratified volume; in heating mode, it thinks the space is comfortable long before the bottom of the stairs is.

We prefer to say this before the sale. A customer who closes the bedroom doors and expects the floor to be air-conditioned will be disappointed by an appliance that is working perfectly.

Draining a head in the middle of a building

The final constraint specific to this location, which must be addressed before securing the mounting plate: a head in a stairwell is almost never backed against an exterior wall.

The condensate drain must therefore cover a distance while maintaining a continuous downward slope, through an old structure whose contents are unknown until it is opened. Our method—an inspection window before any drilling, documenting what is in the cavity, and a water-flow test before closing it up—is detailed in our Saint-Étienne-de-Beauharnois article, while the question of when a condensate pump becomes unavoidable is addressed in the one about Les Cèdres.

On this job, the slope was achieved by gravity by taking advantage of the direction of the joists, which is still always our first option: a pump is one more component, with a power supply, a float switch, and a tank to maintain.

Mistakes to avoid in a row house

1. Drill, anchor, or load a party wall to route lines or mount an appliance.
2. Mount an indoor unit on a party wall on the assumption that a quiet appliance will not bother anyone. Structure-borne transmission cannot be judged by ear from the side where you are standing.
3. Install the condenser on the front façade without first checking the borough's regulations.
4. Choose the stairwell unit's position before setting up the ladder that will actually be used.
5. Place a ladder on steps.
6. Forget that the unit will need to be serviced at the same height, four to eight times per season for the filter.
7. Promise that the upper floor will be air-conditioned without stating the requirement that the doors remain open.
8. Neglect access through the alley when preparing the estimate and discover the problem on the morning of the job.
9. Allow defrost water to discharge onto the pedestrian path of a narrow yard.
10. Have it installed by an RBQ-licensed contractor, which complicates both the manufacturer's warranty and any subsequent insurance claim.

HVAC maintenance: how height changes the schedule

• Indoor filters: rinse every 4 to 8 weeks during the intensive-use season, depending on how the room is used. For the stairwell unit, access is the limiting factor, which is why we verify that the filters can be reached during installation rather than at the first service visit.
• Outdoor coil: annual cleaning. In a closed backyard in the Sud-Ouest borough, urban dust and plant debris accumulate without ever triggering an error code: capacity is lost without warning.
• Trays and drains: annual inspection of both indoor units, which are active only in cooling mode, plus the outdoor discharge point.
• Run both indoor units in both modes for about thirty minutes each month, including during the off-season.
• File documentation: serial numbers for each indoor unit with the corresponding room, measured lengths, weighed additional charge, commissioning readings, and a photograph of the nameplate taken while access is still available — a habit that can save you a complete visit four years later.

Grants and documentation

An efficient wall-mounted heat pump installed in a residence may qualify for residential assistance programs, particularly those offered by Hydro-Québec and Rénoclimat. Criteria and thresholds change regularly: we verify eligibility when the file is opened, without announcing an amount in advance. The Chauffez vert program is intended to replace fossil-fuel heating and does not apply to a dwelling already heated with electricity.

One administrative point that matters in an older building: SEER2, HSPF2 and EER2 ratings certify a combination of an outdoor unit and indoor units in a given configuration—which is why three series of AHRI codes are published for each model—and the code recorded in the file must match what was actually installed. We covered this point in our Saint-Anicet article.

Finally, if the home is part of a condominium or the customer is a tenant, prior written authorization from the condo association or property owner must be included in the file before ordering, just like a route survey. Our Saint-Michel article explains this step for a divided co-ownership.

Why entrust your installation to AirGreen

In a row building, expertise is not measured by speed of execution. It is measured by what the contractor refuses to do: not drilling into a shared structure, not mounting equipment where its vibration will affect someone else, not placing a ladder on steps because it would be faster, and not promising that an entire floor will be cooled by a head installed in a stairwell.

What we systematically put in writing before the work begins: the exact outdoor unit model and the reason for that choice, the capacity of each head, room by room, the planned routes, including their lengths and estimated additional charge, the AHRI code corresponding to the actual configuration, the planned access methods and their cost, the exact scope of finishing work, the estimated balance point—and what the system will not do.

We work in Le Sud-Ouest, Saint-Henri, Pointe-Saint-Charles, Petite-Bourgogne, Griffintown, Ville-Émard and Côte-Saint-Paul, as well as throughout Montreal, Laval, Longueuil, the North Shore and the South Shore, providing HVAC installation, commissioning and HVAC maintenance for wall-mounted and multi-zone systems.

Have your project assessed

If you live in a South-West row house or duplex, the first question to ask is not which model to buy: it is which walls are actually available, where the outdoor unit can be placed without disturbing anyone, and how the equipment will be accessed for maintenance. Contact AirGreen for an on-site technical assessment, a survey of the routes and access points, and a detailed room-by-room quote.