Installation of a GREE FreeMatch R32 2-head heat pump (GWHD(24)ND6MO) in Mercier–Hochelaga-Maisonneuve, Montreal

In an urban heat island, the problem is not the peak; it is the duration.

This Mercier–Hochelaga-Maisonneuve project has the smallest total indoor capacity we have installed in this product range: two 6,000 BTU/h heads. This is not a budget constraint. It is a direct response to what the neighbourhood does to the building.

The discussion about model selection was conducted elsewhere, and we will not repeat it here. We published the third port and heating reserve for a Beaconsfield project, the reading of the “min. – max.” line for a Dorval project, the rule that a single head never equals the compressor for a Kirkland project, the line-set length for projects in Dollard-des-Ormeaux and Côte-des-Neiges–Notre-Dame-de-Grâce, and the vertical geometry of a plex for a Lachine project. What follows concerns the local climate and the unit’s behaviour during a heat wave — two topics that the manufacturer’s technical data sheet does not cover.

The context: 154,000 residents, 25.4 km², and 65 green alleys

Mercier–Hochelaga-Maisonneuve has approximately 154,000 residents across 25.4 km², or 5,528 inhabitants per square kilometre. The borough encompasses three districts — Hochelaga-Maisonneuve, Mercier-Est (Tétreaultville), and Mercier-Ouest (Guybourg, Longue-Pointe, Louis-Riel) — with 77 parks, 13 community gardens, five dog parks, the Maisonneuve Market, four museums, and the Olympic Park.

One figure stands out for a heat pump project: the borough has 65 green alleys. This figure is not a municipal curiosity. It is a direct measure of a problem the neighbourhood knows well and is actively addressing — surface mineralization — and this problem changes how an air-conditioning system is sized and installed.

Two 6,000 BTU/h heads: 50% of rated capacity

The home has two enclosed rooms to be conditioned: a primary bedroom and a second bedroom converted into an office. Each received 6,000 BTU/h, for a total of 12,000 BTU/h of installed indoor capacity on a GWHD(24)ND6MO rated at 24,000 BTU/h — a 50% ratio, the lowest in our entire series of articles on this range.

Two honest clarifications, because a 50% ratio deserves to be explained, not defended.

The first: on paper, the smallest unit in the range would have supported these two indoor units, and we in fact did so on a Côte Saint-Luc project with exactly the same pair of capacities. The next size up was purchased here for one reason only — the third zone planned in the front room, which only the GWHD(24)ND6MO can accommodate. The argument was developed for a Beaconsfield project and applies here exactly as stated; its cost in decibels, weight, amperage, and EER2 is also quantified there.

The second: the system's modulation floor is 2,200 W, or approximately 7,500 BTU/h. A single 6,000 BTU/h indoor unit under demand therefore falls below this floor, and the compressor operates in short cycles in that zone. We documented the mechanism for a Saint-Chrysostome project, as well as the finding that a small indoor unit works better when paired with another unit than on its own for a Côte Saint-Luc project. This is the real weakness of this configuration, and we identify it before signing: a client who wants one bedroom to be perfectly modulated independently of the other needs a larger indoor unit or a separate system.

What a heat island does to the cooling load

A heat island is not a metaphor. It is a measurable phenomenon: mineral surfaces — asphalt, concrete, brick, dark roofs — absorb solar energy during the day and release it slowly. In a dense area with little vegetation, the consequence is not so much that afternoons are hotter than elsewhere; it is that the nights do not cool down.

The night no longer resets the counter

The conventional load calculation relies on an implicit assumption: the house cools down overnight. The walls and floors release their heat toward an outdoor environment that has become cooler, and the following day starts again from a lower baseline.

In a heavily built-up area, this reset is only partial. The building's mass remains heat-loaded in the early morning, and the second day of a heat wave starts higher than the first. The third starts even higher. It is not a higher peak that needs to be covered, but a longer plateau.

The design implication is counterintuitive, and it explains this project's 50% ratio: when facing a plateau, a modest capacity that runs continuously is better than a high capacity that starts and stops. A unit that modulates at low output for twelve hours maintains the temperature AND removes moisture from the air, because its coil stays cold long enough to condense moisture—we developed this mechanism for a project in Saint-Édouard. An oversized unit reaches the setpoint quickly, shuts off, and leaves a room that is cool but humid.

That is also why the two selected zones are the bedrooms, not the living room. In a neighborhood where temperatures no longer cool off at night, the room that deteriorates the most is precisely the one occupied at night.

The condenser does not breathe the weather station's air

The second effect is more technical and is almost never explained to a client.

A heat pump in cooling mode rejects heat from the home into the outdoor air, and its performance depends directly on that air's temperature. But the outdoor unit does not breathe the temperature reported by the weather station: it breathes the air at the exact location where it is installed. An asphalt yard surrounded by sun-exposed brick walls can be several degrees warmer than the air over a shaded, grassy lot two blocks away.

The hotter the intake air, the higher the condensing pressure, the lower the available capacity, and the higher the energy consumption—for an otherwise identical unit. The same properly sized model does not deliver the same performance depending on where in the yard it is installed.

Air recirculation is another factor, and it performs poorly in a hot, enclosed space: we published what insufficient front clearance costs for a project in Ahuntsic-Cartierville, and the problem is even worse when the ambient air is already above the neighborhood average.

Where to place the outdoor unit in a heavily built-up neighborhood

Three rules we apply in dense areas of Montreal, none of which cost anything on this project because they were followed before drilling:

1. Shade, yes; an enclosure, no. A unit placed in the shade of a tree, a vegetated fence, or a building overhang operates in cooler air and genuinely benefits from it. A unit enclosed in a decorative cabinet loses far more than it gains because it draws its own discharge air back in — we detailed the three ways to get a condenser awning wrong for a project in Les Cèdres.
2. Not against a brick wall in full sun. A south- or west-facing facade made of dark brick is a heat reservoir: it radiates its heat well into the evening, exactly when the air conditioner is working hardest.
3. The laneway side deserves a closer look. In this borough, 65 laneways have been greened. A planted laneway is not only more pleasant: it is cooler than the same laneway paved with asphalt, and it is a location that deserves serious consideration rather than being ruled out automatically. Siting, clearance, and property-line noise rules apply there just as they do everywhere else — we published the decibel and municipal-regulation analysis for a project in Huntingdon, and our site has a section covering regulations by borough and municipality for Montreal, the North Shore, and the South Shore.

What the technical data sheet does not say about a 33 °C day

Here is the part we consider the most useful in this entire article, and it hinges on something missing from the manufacturer's document.

Cooling capacity is published under reference conditions

The GREE FreeMatch R32 brochure lists a rated capacity of 24,000 BTU/h and a modulating range of 7,500 to 31,400 BTU/h for the GWHD(24)ND6MO. These values are established under standardized test conditions, which is perfectly legitimate: that is what makes it possible to compare two units.

What they are not is a forecast of what the unit will deliver in your yard on July 3 at 33 °C. Cooling capacity decreases as the outdoor temperature rises, for the reason explained above: the condenser has to reject its heat into increasingly unwelcoming air.

And the document publishes no capacity data at high temperatures—no value at 30 °C, 35 °C, or 40 °C. This is exactly the mirror image of a gap we had identified in the other season for a Franklin project: the same brochure advertises heating operation down to -30 °C without publishing the slightest low-temperature capacity figure. The operating range says that the appliance will operate; it does not say how much it will deliver.

The question to ask a contractor

Only one, and it quickly separates the bids:

“What cooling capacity does this appliance deliver at an outdoor temperature of 33 °C, and at what outdoor temperature does the installed capacity stop covering the load of these two rooms?”

A contractor who answers “it’s a 24,000 BTU/h unit” has not answered the question. A contractor who explains that you need to consult the performance tables in the technical manual—not the sales sheet—has shown that they know where the information is. We published a ten-point checklist for a Saint-Chrysostome project to compare multi-zone bids; this question belongs on the list in a heat-island area.

During a heat wave, an appliance that never stops is working properly

The most frequent service call in the three days following a heat wave sounds like this: “the appliance runs nonstop.” In almost all cases, there is nothing to repair.

A wall-mounted air conditioner with inverter technology is designed to modulate, not cycle. When the home’s load equals or approaches the available capacity, the compressor runs continuously at a high output: this is the expected behavior, and it is the most efficient behavior the appliance is capable of. A system that cycled during a heat wave would be seriously oversized.

Five habits that make the situation worse

• Lower the setpoint to 18 °C. An appliance already running at full capacity will not go faster; the room will not reach 18 °C any sooner. It will simply reach a setpoint it cannot maintain, and the appliance will never stop.
• Open the windows “to help.” Every cubic meter of hot, humid air entering is an additional load added to an already saturated system.
• Open the doors to rooms that are not air-conditioned. Two indoor units condition two rooms. With the doors open to the rest of the home, they condition only part of the home, and poorly.
• Neglect the filter in July. A clogged filter causes the fan speed to increase before capacity drops: noise increases before efficiency falls, and that is the first warning sign.
• Wait for a heat wave before calling. Annual maintenance should be scheduled in spring, not during the three days when everyone calls at once.

What we adjust during commissioning for this type of area is the fan speed in automatic rather than fixed mode, the louvers directed forward in cooling mode, a steady setpoint between 23 and 25 °C, and the coil's automatic drying function activated after cooling cycles.

The plaster cornice: one fewer option than elsewhere

The photo of this installation shows the indoor unit mounted just below a molded cornice, in a home with old-style windows. The issue of clearances beneath a molding has been covered for projects in Verchères and Dorval, and we will not revisit it—except for one point specific to the older buildings of Montreal.

In a home from the 1900s to the 1930s, this cornice is very often not an applied wood molding, but a plaster profile formed in place. The difference is decisive at installation: among the three solutions published for Verchères—lowering the unit, removing a section of molding, or changing walls—the second is practically not an option here. A plaster molding formed in place cannot be removed and reinstalled; it must be demolished, and recreating it requires a plasterer and a template, not a trip to the hardware store.

In this type of housing, the decision therefore comes down to only two options, and it must be made during the technical inspection—not with a tape measure in hand on installation day.

Mistakes to avoid in a dense area of Montreal

• Size it larger because the neighborhood is hot. A space is covered over time, not at peak load.
• Choose the outdoor location solely based on aesthetics, without considering what the ground and surrounding walls radiate at the end of the day.
• Enclose the outdoor unit in a cabinet to hide it from the neighbor.
• Read the product sheet as a performance forecast at 33°C.
• Assume that two heads can cool an entire home. They cool two rooms, with the doors closed.
• Remove the electric baseboards after the first winter has proven satisfactory. They remain in place, set 2 to 3°C below the heads' setpoints.

Rebates, warranty, and maintenance

The system qualifies for applicable residential energy-efficiency programs in Quebec, notably Hydro-Québec's LogisVert and Rénoclimat. Chauffez vert does not apply here because the home is already heated with electricity. Eligibility criteria change, so we verify eligibility when opening the file rather than advertising an amount in the quote. The declared AHRI code must match the combination actually installed, or an application may be rejected for administrative reasons.

The warranty is 10 years, extended to 12 years upon product registration with proof of installation submitted to the distributor; we complete the registration at the end of the project.

As for HVAC maintenance: rinse both filters every 4 to 8 weeks during the intensive season, check both pans and both drains, and rinse the outdoor coil annually—which, in a dense area exposed to street dust, pollen, and particles, directly affects performance on the days it matters most.

AirGreen in Mercier–Hochelaga-Maisonneuve and Greater Montreal

At AirGreen, we design, install, and maintain multi-zone wall-mounted heat pump systems in Montreal, Laval, Longueuil, the North Shore, and the South Shore. In Mercier–Hochelaga-Maisonneuve—from Hochelaga-Maisonneuve to Tétreaultville, via Guybourg and Longue-Pointe—the homes are old, the yards are small, the surfaces are paved, and summer nights no longer cool down as they do elsewhere on the island.

A successful project in this context is not determined by the number of BTUs listed in the quote. It depends on where the outdoor unit can breathe, how long the system can modulate at low output, and what we took the time to explain before the first heat wave.