Installation of a 2-head GREE FreeMatch R32 heat pump in Dorval (Montreal agglomeration)

The “min. – max.” line is more useful than the “nominal” line: how we installed 30,000 BTU/h worth of heads on a 24,000 BTU compressor

The homeowners called us with a specific question rather than a vague request: two contractors had told them that 30,000 BTU/h worth of heads on a 24,000 BTU/h outdoor unit “isn’t done.” The house, in a residential area in Dorval, is well maintained: a large open area on the ground floor, molded cornice running around the entire perimeter, applied wall panels and chair rail, and a second zone upstairs. No ductwork; electric heating.

We installed a GREE FreeMatch R32 2-head wall-mounted heat pump with a GWHD(24)ND6MO outdoor unit: 18,000 BTU/h in the open area and 12,000 BTU/h in the second zone, for a total indoor capacity of 30,000 BTU/h. The two contractors were right to ask the question and wrong in their conclusion, for a reason found in a single line of the specification sheet — the one almost no one reads.

The project: a large open area and a secondary zone

The ground floor is essentially one open space: the entrance, living room, and dining room connect, with an opening to an adjoining room and a staircase. This continuity is why an 18,000 BTU/h head is used instead of two smaller ones: in an open space, the capacity needs to come from a single unit capable of projecting air a long distance, not two units sharing the same air.

The second area, upstairs, is an enclosed room used daily that received 12,000 BTU/h. The rest of the house — kitchen, bathroom, and secondary rooms — remains served by its electric baseboard heaters, which were not removed.

What the specification sheet calls “nominal,” and what the machine actually does

A heat pump specification sheet provides two capacity figures, and most quotes use only one. The nominal capacity is a standardized reference point, measured under specific conditions, used mainly to compare units with one another. The line directly below, “min. – max.”, indicates what the unit can actually produce at both ends of its modulation range. On an inverter system, this second line describes real-world operation.

Here is what the FreeMatch R32 brochure publishes for the entire range in cooling mode:

The picture is clear: the GWHD(24)ND6MO is the model in the lineup with the largest reserve above its rated capacity, while the GWHD(42)ND6MO has the thinnest. In other words, two units chosen solely by their nominal rating can behave very differently in a real home.

The detail no one points out: heating and cooling do not scale the same way

When the two lines in the brochure are compared, a pattern emerges, with practical consequences.

• For the GWHD(18)ND6MO, the maximum heating capacity (18,100 BTU/h) is lower than the maximum cooling capacity (19,800 BTU/h). It is the only model in this situation, which means that on this small system, heating is what limits the project.
• For the GWHD(24)ND6MO, the two maximums are identical: 31,400 BTU/h in both cooling and heating. It is the only perfectly symmetrical model in the lineup.
• For the 30k, 36k, and 42k, the maximum heating capacity significantly exceeds the maximum cooling capacity (40,900, 51,180, and 54,590 BTU/h, respectively).

For a two-head project like the one in Dorval, this symmetry of the 24k was exactly what was needed: the reserve is the same in both seasons, and there is no weaker season.

Why 125% indoor capacity works here

30,000 BTU/h of indoor-unit capacity on 24,000 BTU/h nominal capacity equals 125%. The usual calculation stops there and concludes that the system is oversized. The complete calculation continues: when both indoor units call for capacity at the same time, they demand 30,000 BTU/h, and the compressor can produce 31 400The simultaneous demand is therefore fully covered, in both cooling and heating.

This is an important nuance, because with two zones, simultaneous operation is not an unlikely assumption. We explain it in our Vaudreuil-sur-le-Lac article: with two comparable zones occupied by the same people at the same times, the non-coincidence assumption that justifies high ratios on four- or five-zone systems no longer holds, and on a sweltering evening, both indoor units call for capacity at the same time. On a small system, the two units then share an undersized compressor, and neither receives its rated capacity. Here, the 24k’s reserve absorbs precisely this scenario. The ratio is the same on paper; the situation is not.

It’s the same reserve that allowed us, in our Kirkland article, to pair an 18,000 BTU/h indoor unit with a 9,000 BTU/h unit on this outdoor unit: the 24k operates well above its rated capacity, and that is precisely why we choose it for a two-zone project.

Two honest counterpoints, which we always put in writing:

1. These maximums are values measured under test conditions. Capacity drops as the outdoor temperature falls, and the FreeMatch commercial specification sheet publishes no low-temperature capacity data—we made this the subject of our Franklin article. The 31,400 BTU/h is not a January promise, and the balance point was estimated and provided in writing before the order.
2. The modulation range also has a lower limit: 7,500 BTU/h on this model. Neither of our two heads falls below it, so no zone is forced into short cycling—which would not have been true with a 6,000 BTU/h head.

The other lines that mattered

The precharged length is 30 m on the GWHD(24)ND6MO, for a maximum total of 60 m and an elevation difference of 15 m. Our two runs are 11 m and 16 m, for a total of 27 m: the project remains within the factory charge, and no refrigerant was added, leaving the minimum room-size verification unchanged from the nameplate. We explain this reasoning in our Beaconsfield article, and the reverse calculation—of a system requiring an additional charge—in those for Ahuntsic-Cartierville and Anjou.

19.5 A MCA and 25 A MOCP: a single dedicated circuit powers the entire system, with the indoor units powered by the outdoor unit. The panel load calculation is the responsibility of the licensed electrician, as we explain in our Saint-Édouard article.

The third port: the 24k accepts 2 to 3 indoor units. We used only two, and the benefit of keeping this port available is discussed in our Beaconsfield article. Just remember that an unused port today is the only way to add a zone tomorrow without buying a second complete system.

The rest of the GWHD(24)ND6MO specification sheet, for readers comparing quotes:

Living under a flight path: how Dorval changes the project

Dorval has been home to Montréal–Trudeau International Airport since its inauguration in 1941, and Aéroports de Montréal manages a noise climate program with a public mechanism for reporting noise events. For an HVAC project, this context changes two concrete things.

First, the outdoor unit's sound level—58 dB(A) on this model—stops being the determining factor it is elsewhere. That does not remove any obligations: the municipal bylaw still applies at the property line, and it is the immediate neighbor's tolerance, not the ambient noise, that determines whether an installation succeeds. Our Huntingdon article details how sound diminishes with distance and how to address the issue before choosing a location.

Next, and this is the useful point: in areas where windows remain closed for much of the summer, air conditioning stops being a comfort and becomes the only way to make the house livable. But a wall-mounted unit does not ventilate: it recirculates the room's air over a coil and brings in no fresh air, as we wrote in Beauharnois. A house that is not opened up needs an air exchanger, and the heat pump does not replace it. We say this at the quotation stage rather than when the client wonders why the air feels heavy in August despite having a new unit.

Installing a unit in a room with moldings: symmetry versus technique

This is the real challenge of the project, and it has nothing to do with thermodynamics. The chosen wall has a molded cornice at the top, a dado rail, and applied panels at the bottom. A room decorated this way is a composition: it has an axis, regular bays, and the eye immediately notices any object that does not align with it.

Three constraints competing for the same wall

Positioning a wall-mounted heat pump must first meet three technical requirements: a continuous slope for the drain toward the outside, a refrigerant-line exit point that passes through neither a structural element nor an opening, and a mounting plate secured to real wood. A fourth, aesthetic requirement has now been added: the visual axis of the wall composition.

These requirements rarely coincide. Our method is to put them on the table in this order, during the technical visit rather than on installation day:

1. We determine the room's visual axis and the position the client considers correct.
2. We check whether the technology allows it. A perfectly centered unit with a drain rising by two millimeters is a leak scheduled for July.
3. If the two cannot coincide, calculate the discrepancy before drilling. An appliance offset by 40 cm on a symmetrical wall is a constant irritation; opening a ceiling to route the drain differently is an expense. The client must decide, with both answers in front of them.

In Dorval, the outlet could be aligned with the desired bay, and the lateral clearance determined the final few centimetres.

The Cornice Is Not the Ceiling

Here is the subtlety most installers miss on this type of wall. The required clearance above the enclosure is measured to the nearest obstruction, and on a wall with a cornice, that obstruction is not the ceiling: it is the moulding, which projects several centimetres into the room.

A substantial cornice therefore forms a shelf above the return-air grille. Two consequences follow: the actual clearance is smaller than what you measure with a tape from the ceiling, and the return air follows the underside of the moulding instead of rising freely. An appliance installed too tightly beneath a cornice recirculates its own supply air and settles on a false return-air temperature. The possible options — lowering the appliance, removing a section of moulding, or changing walls — are detailed in our Verchères article. What we add here is that the measurement must be taken beneath the moulding, never at the ceiling, and it must be taken before mounting the plate.

Let us also recall the rule we stated in our Anjou article: you do not recess a wall-mounted unit into a niche, nor enclose it in a decorative cabinet, even if it is very well made. The manufacturer's clearances apply to a free-standing enclosure.

Applied panels, and why the decision must be made before decorating

The applied panels and chair rail create two distinct difficulties.

The first concerns the mounting: the mounting plate must not rest on any raised moulding detail, otherwise it will be out of level — and an out-of-level plate means a condensate pan that loses its slope. On this wall, the plate was installed in the smooth area above the chair rail, anchored to the framing.

The second concerns the finish. A surface-mounted raceway crossing applied panels cannot be made discreet: it cuts through the frames, creates shadows, and no painter can fix that. The choice must therefore be made beforehand, between routing through the wall and routing through the adjacent room. And if decorating work is planned, it must be done before installation, never afterward — we demonstrated this in our Sainte-Marthe article, where wallpaper raised the same question. Let us add one point homeowners never anticipate: moulding profiles are discontinued, and a section removed to allow an appliance to pass cannot always be replaced identically.

Two whites are not the same white

A wall-mounted unit’s casing is white. The trim in a decorated room is white too, but rarely the same white, and a cream-coloured wall makes the difference even more noticeable. This is not a defect in the unit; it is a job-site reality that is best observed in person before ordering, simply by bringing the unit close to the wall or comparing samples.

The conclusion follows, and it is firm: never paint the casing of an indoor unit. Paint migrates into the louver joints, soils the front-panel gasket, adheres poorly to the plastic casing, and makes any maintenance disassembly difficult. If the colour matters that much, address it through the choice of wall, lighting, and finish around the unit, never with a paintbrush.

Raking light reveals everything

On this project, the light sweeps across the wall at an angle. Raking light is unforgiving: it reveals every patch, bump, and filled-in anchor that frontal lighting would conceal. In practical terms, this means repairs must be feathered much more broadly than usual, and the issue should be discussed before the work begins. Patching and painting are not part of the HVAC scope of work, which we state in the quotation—our Saint-Bernard-de-Lacolle article addresses this scope issue in detail.

What the room requires for adjustment

A decorated open-plan area cannot be adjusted like a bedroom. Three adjustments were made during commissioning:

• Angle the louvers forward rather than downward in cooling mode, because people sit and receive the air beneath the unit, and a downward-directed stream creates an unpleasant draft. The opposite applies in heating mode.
• Use automatic fan speed rather than setting it high: in an open space, reach matters more than instantaneous airflow. The behavior of the air stream along the ceiling is explained in our Sainte-Martine article.
• Keep the setpoint stable. On a modulating unit, changing the setpoint by three degrees several times a day produces exactly the abrupt starts one is trying to avoid.

Mistakes to avoid on a two-head project in a finished home

1. Choosing the outdoor unit based solely on nominal capacity. The “min. – max.” line tells the real story of the unit’s performance.
2. Jumping to the conclusion that it is oversized. 125% indoor capacity is a figure, not a diagnosis: the comparison with the modulated maximum is what settles the matter.
3. Drill before deciding on the visual axis. The mounting plate cannot be moved without leaving traces.
4. Measuring the clearance above to the ceiling instead of to the underside of the eave.
5. Painting the casing or enclosing it in decorative millwork.
6. Removing the baseboard heaters. Two heads serve two zones, not an entire home.
7. Believing that a heat pump replaces an air exchanger in a home where the windows remain closed.

Maintaining a dual-zone system

Two zones mean two sets of indoor filters, two condensate pans, and two drains. Rinsing the filters takes about ten minutes every four to eight weeks during the intensive-use season; this is in addition to annual cleaning of the outdoor coil, checking the drains before the cooling season, and running fan-only mode for twenty to thirty minutes after the last cooling cycle to dry the coil. A dirty filter first causes the fan speed to increase, and therefore the noise: in an open-concept area where people entertain, this is the first symptom occupants notice.

Rebates and eligibility

A heat pump installed alongside electric heating may qualify for energy-efficiency programs currently in effect in Quebec, including Hydro-Quebec's LogisVert and Rénoclimat. Chauffez vert is intended for conversions from oil or propane and does not apply to a fully electric home. The criteria and amounts change, so we validate them when opening the file. One administrative point not to overlook: the declared AHRI code must correspond to the combination actually installed; otherwise, an application may be refused for a purely documentary reason.

Why entrust this type of project to AirGreen

A two-head project in a finished home comes down to trade-offs that the sales brochure does not show: which line on the panel schedule to read, where the visual axis gives way to a drain's slope, how far clearance is measured beneath an eave, and what is written in the quote rather than left to appear at the end of the project. At AirGreen, we install and maintain HVAC systems in Montreal, Laval, Longueuil, the North Shore, and the South Shore, and we provide a commissioning file: model and serial numbers for each room, measured line lengths, commissioning readings, the circuit identified at the panel, and the warranty registration date.

For a wall-mounted heat pump installation, a dual-zone system, or annual maintenance in Dorval, the West Island, or elsewhere in Greater Montreal, contact our team: we measure, explain the trade-offs, and put in writing what the unit will—and will not—do.