Installation of a 5-head GREE FreeMatch R32 multi-zone heat pump in Sainte-Justine-de-Newton (Vaudreuil-Soulanges RCM)

Five 6,000 BTU/h indoor units on a 42,000 BTU/h compressor: when the number of zones requires an oversized unit

At AirGreen, this Sainte-Justine-de-Newton project is the one where we spent the most time explaining a technical disagreement rather than selling. The homeowners wanted five zones. The load calculation came to 30,000 BTU/h for the entire house. And the GREE FreeMatch R32 lineup offers only one outdoor unit capable of powering five indoor units: a 42,000 BTU/h unit.

In other words, the number of rooms to be served required a compressor that was significantly larger than the house. This is a situation that commercial documentation never addresses, and that we are publishing here in full — the comparison we presented to the clients, the solution we recommended, the one they chose, and what we did to make the configuration work anyway.

The context: a country home with small, enclosed rooms

Sainte-Justine-de-Newton is one of the most rural municipalities in the Vaudreuil-Soulanges RCM: just under one thousand residents, more than 84 km² of territory, almost all of it in an agricultural zone, with dairy farms, large-scale grain farming, and an artisanal goat cheese producer near Péveril. Newton Township was proclaimed in 1805; the west was settled by Scots from Glengarry and the east by French-speaking families from the seigneury of Vaudreuil. The resulting housing stock consists of country homes, often older, rarely designed around a large central open space.

The target house is a clear example: five small, enclosed, partitioned rooms, with no open-plan area, electric baseboard heating, and no ductwork.

Five identical indoor units, all at the smallest available capacity. Thirty thousand BTU/h of indoor capacity on a compressor rated at 42,000 BTU/h, or 71% — the lowest ratio we have published.

The outdoor unit is the GWHD(42)ND6MO, certification AHRI 214931590 in non-ducted configuration (214931596 ducted, 214931600 mixed), MCA 30 A, maximum overcurrent protection 45 A, factory charge of 2,700 g of R32, 79 kg.

The real problem isn’t oversizing; it’s the floor

A compressor that is too large for the heads does not cause what one might imagine. No head will ever be starved of refrigerant: there is more than enough for everyone, even all five zones calling simultaneously at −25 °C. That is not where the problem lies.

It gets stuck at the low end. The GWHD(42) technical sheet gives a heating modulation range of 8,870 to 54,590 BTU/h. The lower figure is a property of the system, not of each head: it is the smallest amount of heat this compressor can produce continuously, across all ports.

Compare that with a 6,000 BTU/h head.

The system floor exceeds by nearly 50% what a single small room can absorb. In practical terms: when the office calls for heat alone on a Tuesday afternoon, the compressor cannot come down to meet it. It produces its minimum, satisfies the room within a few minutes, stops, waits, and restarts. Even when adding two zones — 12,000 BTU/h — we barely exceed the floor. This house is truly in continuous-modulation comfort only when three or more zones call simultaneously, that is, in cold weather, which is fortunately when the system works the hardest.

The modulation-floor mechanism is explained in detail in our Saint-Chrysostome article. What is specific to this project is that the floor is not an occasional edge case: it shapes the behavior of the entire system.

What we recommended: two units rather than one

Here is the comparison we provided to clients, based solely on the manufacturer’s data.

The decisive point is the bottom line. Two smaller compressors mechanically have lower modulation floors in absolute terms. A 6,000 BTU/h head connected to a GWHD(18) has a much healthier relationship with its compressor than when paired with a 42,000. The minimum modulation line appears on the exact model’s specification sheet — it’s a line we encourage every homeowner to have their contractor point out before signing.

Two systems also provide independent operating modes—the living room can cool in May while the bedrooms are heating—and genuine redundancy, a subject covered in our Franklin article.

Why only one unit was installed anyway

We also write about what goes against our recommendation, because that is what makes an opinion credible.

The clients chose solution A for four perfectly rational reasons: only one outdoor unit to install and maintain; one dedicated electrical circuit instead of two, which matters on an already heavily loaded rural electrical panel (addressed in our Saint-Édouard article); only one annual maintenance visit; and a lower installation cost, since two systems require two drains, two commissioning procedures, and two outdoor bases.

Our role ends there: present the comparison in writing, explain the consequence, and deliver impeccable work on the chosen solution. What we refuse to do is imply that the selected configuration is optimal when it is an acknowledged compromise.

What we did to make this configuration work

Four measures, all taken during commissioning and recorded in the file:

1. An anchor zone. The living room keeps an active setpoint at all times rather than shutting down overnight, ensuring that the compressor always has at least one substantial load to serve.
2. Coupling the small zones. The setpoints were grouped so that the rooms call in pairs rather than individually—the coupling mechanics are detailed in our Saint-Urbain-Premier article.
3. The minimum fan speed was increased by one setting in the two least-demanding zones, lengthening the cycles instead of chopping them up.
4. The baseboards were kept throughout, with a written balance-point note provided to the homeowners. At 71%, they are not merely symbolic backup heat: they are what covers an isolated room that the compressor has no reason to start up for on its own.

The five runs total 43 developed metres—the house is compact—so the whole system remains below the 50-metre precharge, and no refrigerant was added.

The load calculation: why 6,000 BTU/h per room is not a guess

Everything above rests on one figure: 30,000 BTU/h for this house. It is worth explaining where it comes from, because this is the step that half of competing quotes skip entirely.

What a load calculation actually contains

One room at a time, we add up what goes out and subtract what comes in:

• the room's envelope surfaces — exterior walls, a ceiling beneath an attic, and a floor over a crawl space or ground — and the actual thermal resistance of each assembly, which depends on the construction year and work completed since;
• fenestration, calculated separately by orientation, because a south-facing window and a north-facing window of the same size behave completely differently;
• air infiltration, determined by the building's airtightness and the room's position;
• the internal gains — occupants, lighting, and appliances — which reduce the heating load and increase the cooling load;
• the municipality's design outdoor temperature, taken from regulatory climate data rather than the coldest day anyone remembers.

Why the square-foot rule fails

Two 12 m² rooms in the same house can have loads ranging from one to twice the other. One is a corner room, with two exterior walls and a large window; the other is an interior room, surrounded by heated rooms, with only one small opening. A floor-area rule assigns them the same head. The calculation gives them two different ones.

The reverse is also true, and this is what causes the most oversizing: a newer building envelope may require about half the capacity of a 1970s house of the same size — we discuss this point in our Saint-Lazare article. A contractor who applies ratios learned from older housing stock systematically installs units that are too large, and an oversized head does exactly what nobody wants: it short-cycles, fails to dehumidify, and is noisy because it starts at high output instead of modulating down.

Heating and cooling are two calculations, not one

Each room produces two figures. The west-facing room may be the most demanding to cool and one of the easiest to heat; the room above an unheated garage does the opposite. With a multi-zone system, each head's capacity is selected by knowing both figures, understanding which one governs in the actual occupancy conditions — and keeping in mind that the entire system can operate in only one mode at a time.

What the calculation changes more significantly in a multizone system than in a central system

This is the argument we consider the most important point of this article.

In a central system, an error in distributing capacity among rooms can be corrected: the dampers can be rebalanced, a drop can be modified, and airflow can be adjusted. Capacity is shared and redistributed.

With a multizone system, each room's capacity is fixed in the equipment. A 6,000 unit in a room that required 9,000 will remain insufficient for the entire system lifespan, and the only solution is to replace the indoor unit—which means recovering the refrigerant, pulling a vacuum again, weighing the charge, and recommissioning the system. A calculation error in a central system can be fixed with a screwdriver. In a five-head multizone system, it takes a truck.

The data we request, and what you should require

We systematically ask for the construction year, insulation history, and window replacement date, and we measure the rooms rather than relying on the original plans. Anything that cannot be verified is written as an assumption in the report, not folded into a total.

On your end, a serious HVAC quote should be able to provide, upon request, the calculated load for each room—not one overall figure for the house, and especially not a capacity justified by “that's what we usually install.” The complete multizone quote-comparison checklist is in our Saint-Chrysostome article.

Installation details

The indoor unit visible in the photo is mounted at an angle, tight against the ceiling, with the piping outlet on the right and a horizontal line cover immediately leading to the corner of the room—the outlet side determines the condensate drain side and must be decided before securing the mounting plate. The display indicates 69, meaning a setting of approximately 20.5 °C in Fahrenheit, left in place after commissioning. The behavior of the drain network on a five-head installation is covered in our Les Cèdres article, and condensation inside an indoor line cover in the Saint-Louis-de-Gonzague article.

Mistakes to avoid

• Add up the indoor units to determine system capacity. Thirty thousand BTU/h of indoor units do not make a 30,000 unit, nor a 42,000 unit that can be used room by room.
• Choose the number of zones before performing the load calculation. That is what required an oversized compressor here.
• Ignoring the minimum modulation line in the technical data sheet. In a house with small rooms, it is the most important line in the table.
• Standardizing all indoor units at 9,000 BTU/h to simplify inventory, even though the calculation calls for 6,000.
• Removing the baseboard heaters from a 71% configuration.
• Accepting a capacity without written justification for each room.

Maintenance and next steps

Five identical filters, meaning only one reference to retain and keep in reserve—the only clear advantage of a completely uniform configuration. A single outdoor coil in the middle of an agricultural area is exposed to field dust, crop residue, and windblown snow, none of which ever triggers an error code, and annual rinsing of the coil is essential to maintaining performance rather than improving it. The issue of dirt buildup in rural environments is explored in our Saint-Télesphore article, about the neighboring municipality.

As for financial assistance, since the house is heated with electricity, programs aimed at replacing a fossil fuel do not apply; the relevant options remain Hydro-Québec's energy-efficiency programs and Rénoclimat, whose terms we verify when the file is opened. The declared AHRI reference must match the configuration actually installed. The warranty is 10 years, extended to 12 years upon registration with the distributor and proof of installation; we complete the registration at the end of the project.

AirGreen in Sainte-Justine-de-Newton and western Vaudreuil-Soulanges

We regularly work in the agricultural area west of the regional county municipality—Sainte-Justine-de-Newton, Saint-Télesphore, Sainte-Marthe, Saint-Polycarpe, and Rigaud—where rural homes present sizing challenges that differ greatly from those of newer suburbs. A compartmentalized layout is not a drawback; it actually makes a multi-zone system especially suitable, provided someone has performed the calculations before choosing the number of indoor units.

We carry out this type of HVAC installation and HVAC maintenance in Montreal, Laval, Longueuil, the North Shore, and throughout the South Shore. For a multi-zone project, the first useful step is not a price quote: it is an on-site assessment and a room-by-room load calculation provided in writing.