Installation of a GREE FreeMatch R32 two-head wall-mounted heat pump in Marieville, Rouville RCM (Montérégie)

Two outdoor units on the same house, and neither knows that the other exists

Marieville is not a rural village. It has been a town since 1905, originating from the Monnoir seigneury granted to Claude de Ramezay in 1708, becoming a parish in 1832 and a municipality in 1858, merging in 2000 with the parish of Sainte-Marie-de-Monnoir, and having a population of 11,332 people spread over 63.23 km² in the 2021 census, about thirty kilometers east of Montreal. This means neighborhoods of closely spaced brick houses, covered front entrances, lots where the available technical locations can be counted on one hand—and, increasingly often, houses that already have an outdoor unit before a second one is installed.

That is exactly the case here. The new outdoor unit of the heat pump was installed on aluminum rails on the concrete slab of the covered entrance. And on the other side of that same porch, against the back wall, there is already another one.

We have published many pages about the neighbor’s condenser. This one is about yours—the second one.

The problem no one checks: two units breathing each other’s air

The mechanism is established, and we are not reinventing it: in Ahuntsic-Cartierville, we documented that air discharged against a nearby obstacle returns to the intake, that capacity drops in cooling mode, that defrost cycles become more frequent in heating mode, and above all that no alarm indicates it. In Oka, we applied this to two units sharing the same volume—“neither machine knows that the other exists”—but in the case of the neighbor’s condenser, on the other side of a fence.

The Marieville case is different, and easier to resolve, because both units belong to the same person:

• In air conditioning, both reject hot air. Two units facing each other, or blowing into the same enclosed area closed on three sides, heat each other's intake air. Both lose capacity on the hottest day, exactly when you notice it.
• In heating mode, both discharge air that is colder than the surrounding air, carrying the moisture they have just removed. The appliance downwind of the other receives air that is both colder and more humid — and moisture on a heat exchanger already colder than the surrounding air means frost. We published this mechanism for Pointe-Claire regarding neighboring vents; it applies fully from one condenser to the other.
• Our Saint-Simon pages covered the related case of a pool appliance, which discharges cold air while an air-conditioning condenser discharges hot air: same conclusion, no fault code.

What we did here can be summed up in one sentence, and it is the rule we now follow whenever an existing appliance is present: we determine the discharge-air direction of the appliance already in place before choosing the location of the new one, not afterward. The two units were positioned so that neither blows toward the other's intake, with the greatest possible clear space between them — which, on a covered entrance, cost one metre of extra copper piping and nothing else.

Two systems, two circuits, two disconnect switches, two files

The second issue raised by a second installation is administrative, and it is better to resolve it on the day of installation than three winters later.

• Electrical systems. Each system has its own dedicated circuit and disconnect switch. No shared circuit, no shared disconnect switch, and each circuit breaker identified at the panel by the name of the appliance it powers — the distinction between a circuit breaker, which protects a circuit, and a disconnect switch, which isolates an appliance, has been published in full for Rosemont–La Petite-Patrie. The reason is practical: when a technician cuts power to work on one, they must not shut down the other without realizing it.
• Maintenance. Two appliances mean two heat exchangers to rinse, two sets of filters, and two records. We schedule them for the same annual visit, in the same file, so the owner does not have two calendars to maintain.
• The warranty. This is the point customers never see coming: two appliances of different ages, often from different brands, have two separate warranties, two registration dates, and two points of contact. A defect in one says nothing about the other. We therefore record both appliances in the handover file, along with their serial numbers and dates, including the one we did not install.
• The diagnosis. A homeowner with two systems says, “the heat pump is no longer heating.” The first question on the phone has become: which one?—a seemingly stupid question that saves a service call one time out of three.

And the fundamental decision—two separate systems rather than a single multi-zone system—was argued elsewhere, and we will not revisit it here: Franklin published the honest list of cases where two systems are better than one, Anjou treated it as an architectural decision rather than a capacity decision, and Vaudreuil-sur-le-Lac provided the full comparison. The useful summary: a single compressor for the entire house is a single point of failure, and two systems provide redundancy that no one values until the first breakdown.

The unit is by the front door, and it is the only place you will see every day

The second remarkable fact about this project is the location itself. The unit is neither in the backyard, nor in a side passage, nor beneath a porch: it is on the covered front entrance, on the façade, a few steps from the door.

The elimination sequence that leads there was published for Plateau-Mont-Royal—backyard, alley, façade, balcony, roof, in that order—and Le Sud-Ouest documented the case where only the rear remains and nothing else. Questions of municipal regulations concerning mechanical equipment visible from the street fall under local zoning and were addressed in Huntingdon; we verify them in the file and publish no standards here. The visual screen, with the four ways to get it wrong, belongs to Westmount.

What this page adds is what changes when the chosen location is the one everyone sees.

What the façade changes, in practical terms

Candiac published the exact opposite of this situation: a unit installed on a blank gable wall that no one ever walks alongside, and whose annual visit will be the only inspection it ever receives. In Marieville, the opposite is true in every respect:

1. The visitor's path. Anyone who rings this doorbell passes by the unit. The service clearance is therefore not merely a technical clearance; it is a passageway. We measured it as a corridor, not as a maintenance area.
2. Air blowing onto people who are waiting. The unit blows forward, toward the gallery opening. We verified that the airflow does not cross the area where people stand to ring the bell — in summer, it is warm air on a visitor's back; in winter, a cold draft across the threshold. Dollard-des-Ormeaux stated the principle in the case of a patio: blown air is uncomfortable in itself, regardless of the noise.
3. Noise at the door. This model is rated at 58 dB(A) at high speed. That is modest, but an entrance threshold is a place where people talk. Silent mode is activated during commissioning — it is delivered disabled, as we noted for Dollard-des-Ormeaux — and the complete reading of sound levels and their attenuation belongs to Huntingdon.
4. Water, and ice. This is non-negotiable. A concrete slab in front of a door receives summer condensate and winter defrost water. Les Cèdres put it plainly: September water is October ice, and a drain termination should never be above a driveway, step, or entrance. Vaudreuil-sur-le-Lac called ice at the threshold what it is — a fall hazard, not a maintenance inconvenience — and Saint-Mathieu published the difference between a vertical face, which drains, and a slab, which retains water. The visible flow marks on the concrete in this photo are precisely what we are talking about: the water will go somewhere, and if no one decides where, it will decide for itself. Here, the flow was directed away from the threshold and out of the snow-removal path.
5. Snow removal from the entrance. The front entrance is shovelled every day in winter. The unit must be neither in the shovel's path nor where snow is pushed.
6. What the house is worth. The value of a heat pump at the time of resale was addressed in Montréal-Est — the inspector performs an operating test, not an installation inspection. We add only one observation: on the front façade, the visible quality of the work becomes either a permanent selling point or a permanent criticism. Aligned line sets, a straight conduit cover, sealed penetrations with drip flashings, and a clean enclosure are not mere fussiness in that location.

The gallery roof above the equipment deserves one mention and only one: the rules for a horizontal surface above outdoor equipment, water passing through the boards, and the fact that a heat exchanger never rinsed by rain becomes progressively fouled have been published in Sainte-Christine, Saint-Théodore-d'Acton, and Les Cèdres. We will not revisit them.

The installed equipment and the data behind the decision

GREE FreeMatch R32 2-head wall-mounted heat pump, outdoor unit GWHD(24)ND6MO, AHRI 214931587 in a ductless configuration, ENERGY STAR certified and cold-climate certified.

Distribution: 18,000 BTU/h in the open ground-floor area and 12,000 BTU/h upstairs, for a total of 30,000 BTU/h, or 125% of the nominal capacity. Having the indoor capacity exceed the outdoor capacity is normal in a multi-zone system, and the complete rationale was published in Dorval; the key point is that the total remains below the modulated maximum of 31,400 BTU/h and the two heads never call for their full capacity at the same time.

The choice of the 24,000 rather than a larger cabinet is directly related to this page's subject: 51 kg and 58 dB(A) at the front entrance, rather than 78 kg and 63 dB(A). On a façade, weight and noise matter as much as capacity—and the rest of the home's load is already covered by the second system.

Developed lengths: 6 m and 13 m, for a total of 19 m, including elbows and risers—the actual path length, never the distance measured on a plan. The total remains below the 30 m precharge, so no R32 was added, and the minimum A2L room-area check was redone using the factory charge of 1,700 g. Approximately 3 m of elevation gain over the permitted 15 m.

The binder visible in the photo is not an oversight: it is the handover file, left on-site and reviewed with the homeowners before we leave. Its contents — commissioning readings, developed line-set lengths, final charge, serial numbers for each component, and warranty registration — have been documented in Montreal East, Villeray, and Très-Saint-Rédempteur. The only thing we add here, because the home has two systems: both are included, including the one we did not install.

Mistakes to avoid when there is already an outdoor unit

• Choosing the location of the new unit without determining the airflow axis of the old one.
• Placing two condensers facing each other, or in the same nook enclosed on three sides.
• Sharing a circuit or disconnect switch between two systems.
• Leaving the breakers unidentified at the panel.
• Assuming that the new unit's warranty covers the old one, or vice versa.
• Directing water runoff toward a threshold, step, or entrance that is cleared of snow daily.
• Treating a service clearance at the front as a technical area rather than a passageway.
• Leaving silent mode disabled on a unit installed three metres from an entrance door.

Rebates

The unit is certified ENERGY STAR for cold climates, which is the gateway to the programs currently in effect in Quebec, notably LogisVert and Rénoclimat. The presence of an existing system may affect eligibility depending on the program and on whether the new unit replaces or supplements the equipment already in place: this is precisely the kind of detail that must be verified in the file, using the exact AHRI numbers, before ordering. The criteria change and third-party sources contradict one another; we publish no amounts.

Where we operate

At AirGreen, we carry out HVAC installation and HVAC maintenance for wall-mounted, multi-zone, and central heat pumps in Montreal, Laval, Longueuil, the North Shore, and the South Shore, including the Rouville RCM — Marieville, Richelieu, Saint-Mathias-sur-Richelieu, Sainte-Angèle-de-Monnoir, Saint-Césaire, Rougemont, Ange-Gardien, Saint-Jean-Baptiste, and Saint-Paul-d'Abbotsford. Adding a second system to a home that already has one is not the same operation as a first installation, and the difference comes into play before drilling into the wall.