A rooftop installation designed for the comfort of two zones and the realities of a Montreal building
In the Ahuntsic-Cartierville area, buildings often present constraints that differ significantly from those of a recently built single-family home: restricted access, flat roofs, limited clearance around mechanical equipment, complex routes for refrigerant lines, and immediate proximity to neighboring properties. For this installation, our AirGreen team had to integrate a Fujitsu Aquila XLTH dual-zone heat pump on the roof of a building while ensuring a stable, accessible installation adapted to Montreal’s winter conditions.
The visible result in the photo is a Fujitsu AIRSTAGE outdoor unit operating with R32 refrigerant, installed on an elevated structure. This configuration supplies two indoor units from a single outdoor unit, reducing rooftop equipment congestion while providing separate temperature control in two areas of the building.
For this type of project, workmanship quality depends not only on the choice of equipment. The support structure, clearances, routing of the lines, protection against snow, vibration management, and accessibility for maintenance are equally important to preserve the system’s performance over the years.
Why choose a Fujitsu Aquila XLTH dual-zone heat pump?
A dual-zone heat pump is particularly relevant when a property owner wants to cool and heat two separate rooms or sections without installing two separate outdoor units. Each indoor unit has its own control, allowing the temperature to be adjusted according to the actual use of each zone.
In an Ahuntsic-Cartierville building, needs can vary considerably from one space to another. A room exposed to the sun may require more air conditioning in the afternoon, while a bedroom on the north side may need heating earlier during the cold season. A multi-zone system therefore makes it possible to distribute comfort more effectively without imposing the same temperature everywhere.
The Fujitsu AIRSTAGE Aquila range offers several connection options. Depending on the outdoor unit selected, H-series systems can be combined with wall-mounted units, Slim Duct concealed units, compact cassettes, or medium-static-pressure units. Fujitsu documentation also indicates that certain cold-climate versions can operate in heating mode down to -26 °C, an essential criterion for an installation in Montreal.
For this project, the dual-zone configuration met several objectives:
- serve two spaces with a single outdoor unit;
- offer independent control in each zone;
- limit the space occupied on the roof;
- provide heating and cooling with the same equipment;
- reduce the number of exterior penetrations and connections;
- facilitate maintenance by grouping the main components into a single appliance.
An outdoor unit installed on a flat roof
One of the most important elements of this installation is its location. The outdoor unit was positioned on a flat roof, a common situation in Montreal’s central neighborhoods, particularly in Ahuntsic-Cartierville.
A rooftop installation should never be improvised. The building’s structure, roof drainage, snow accumulation, wind, clearance around the fan, and future access for technicians must all be considered.
In the photo, the unit is installed on a raised metal support, which itself rests on wooden sleepers. This configuration offers several practical advantages.
Keep the unit above snow and water
A heat pump used in winter periodically produces water during defrost cycles. If the unit is installed too close to the roof membrane, this water can freeze around its base, block drainage, or encourage ice buildup beneath the appliance.
The clearance beneath the unit allows water to drain more freely. It also reduces the risk of snow obstructing the lower part of the outdoor coil.
In Montreal, an outdoor unit installed at roof level can quickly become surrounded by windblown snow. The support height must therefore be determined based on the building’s actual environment, not solely according to a standard minimum measurement.
Distributing the load without damaging the membrane
The cross members placed beneath the structure help distribute the weight of the unit and support over a larger surface area. This approach helps prevent excessive load concentration on the membrane.
During a rooftop HVAC installation, we also check that the support elements do not create sharp or abrasive points that could damage the roofing. Contact with the membrane must be stable, clean, and compatible with the applicable building recommendations.
Limiting vibrations transmitted to the building
The supports for a rooftop heat pump also play an acoustic role. A poorly secured unit can transmit vibrations to the structure, particularly in buildings where bedrooms or living units are located directly beneath the roof.
The machine's positioning, the rigidity of the support, and the use of appropriate support points help limit structural noise. This precaution is important even with a variable-speed compressor, since any mechanical vibration can be amplified by a roof or lightweight framing.
A clear installation to preserve airflow
The photographed Fujitsu outdoor unit has a large front fan. Its operation depends on sufficient airflow through the coil and in front of the discharge grille.
We therefore left clear space in front of the unit. No wall, duct, or rooftop equipment directly obstructs air discharge. This arrangement reduces the risk of recirculation, meaning the return of discharged air toward the coil.
Excessive recirculation can lead to several consequences:
- reduced heating capacity;
- increased electricity consumption;
- more frequent defrost cycles;
- abnormally high operating pressure;
- premature compressor wear;
- a drop in performance during periods of extreme cold.
The right side of the unit also has space to access the service panel and connections. This access is essential for performing electrical checks, measuring pressures, inspecting components, or servicing the service valves without moving the entire machine.
R32 refrigerant: a visible feature on the unit
The marking R32 is clearly visible on the front of the unit. This refrigerant is used in several new generations of heat pumps because of its thermodynamic properties and lower global warming potential than certain older refrigerants.
R32 is classified A2L, which means that it has low flammability. This classification requires rigorous installation in accordance with the manufacturer's requirements, particularly with regard to:
- brazing and connection methods;
- leak testing;
- the amount of refrigerant;
- vacuum evacuation;
- the handling of tools and instruments;
- the dimensions of the refrigerant lines;
- the clearances and volumes applicable to indoor spaces.
An R32 heat pump must not be installed like an older system without taking these requirements into account. Technicians must use procedures and equipment compatible with this refrigerant.
Independent operation of the two zones
In a Fujitsu multizone system, each indoor unit can be controlled separately. Occupants can therefore choose a different temperature for each space, adjust the fan speed, and select different comfort settings.
However, it is important to understand a key characteristic of multizone systems: the indoor units can operate at different temperatures, but they generally must remain in the same main mode. The system can heat several zones or cool them, but it cannot heat one room while cooling another at the same time.
This information should be explained before installation, especially in buildings where the two zones have very different exposures. Proper capacity selection and thoughtful placement of the indoor units help limit conflicting demands.
Capacity should not be selected simply by adding up the indoor units
Multizone systems sometimes allow a total indoor capacity to be connected that exceeds the outdoor unit's nominal capacity. According to Fujitsu, certain combinations can reach up to 130% connected capacity.
However, this does not mean that the outdoor unit will automatically produce the full combined rated capacity of all the indoor units when they operate simultaneously. The available capacity is distributed according to demand and the limitations of the outdoor unit.
For a two-zone heat pump, we must therefore analyze:
- the area of each room;
- the number and size of windows;
- solar orientation;
- insulation level;
- ceiling height;
- air infiltration;
- the use of each zone;
- the internal loads generated by occupants and appliances;
- the heating capacity required at low temperatures.
A common mistake is to choose two oversized indoor units, assuming that a higher rated capacity will automatically provide greater comfort. In practice, an oversized system may operate in short cycles, dehumidify less effectively in summer, and produce greater temperature fluctuations.
Managing lines and wiring on the roof
The photo shows the lines and cables leaving the outdoor unit and heading toward the building. On a flat roof, their routing must be organized to avoid traffic areas, water accumulation, and abrasive contact with the membrane.
The refrigerant lines carry refrigerant between the outdoor unit and the two indoor units. They must be properly sized, insulated, and protected against ultraviolet rays, the weather, and mechanical damage.
The insulation must not have openings that allow water to enter. When moisture seeps into the insulation, it can reduce its effectiveness, cause condensation, and accelerate material deterioration.
We also pay particular attention to the bends in the lines. A pipe bent too sharply can create a restriction, disrupt refrigerant flow, and complicate oil return to the compressor.
Mistakes to avoid when installing a multi-zone system on a roof
An installation like this may seem simple because it includes only one outdoor unit. In reality, several mistakes can significantly reduce the system’s lifespan.
Installing the unit too low
An insufficiently elevated base exposes the equipment to snow, ice, and meltwater. The unit must maintain adequate clearance throughout the winter season, not just on the day of installation.
Blocking the service panel
A unit placed too close to a wall, parapet, or other equipment becomes difficult to service. Intervention costs and duration may then increase unnecessarily.
Neglecting vibration transmission
A unit may be quiet in the air while transmitting a humming sound to the structure. The support must be evaluated based on the type of roof and the proximity of occupied spaces.
Choosing capacities without performing a load calculation
Simply adding up the BTUs of the indoor units is not a complete selection process. Sizing must account for the simultaneous operation of both zones and the outdoor unit’s actual capacity.
Ignoring piping length and elevation limits
Multi-zone systems have specific limits for the total piping length, the length of each branch, and the elevation difference between the units. These limits vary by model and must be verified before work begins.
A heating and cooling solution suited to Ahuntsic-Cartierville
This Fujitsu Aquila XLTH dual-zone heat pump installation in Ahuntsic-Cartierville demonstrates how important mechanical and structural details are in an urban HVAC project. Choosing a multi-zone unit made it possible to serve two spaces from a single outdoor unit, while the elevated installation addressed the constraints of a Montreal flat roof.
The Fujitsu AIRSTAGE R32 unit was positioned to maintain good airflow, provide access to the service panel, and leave clearance beneath the machine for snow and defrost water. The support distributes the load and helps stabilize the system without adding multiple pieces of equipment to the roof.
At AirGreen, we carry out this type of multi-zone heat pump installation in Montreal, Laval, Longueuil, the North Shore, and the South Shore. Each project is assessed according to the building’s configuration, the occupants’ actual needs, and the site’s specific conditions.
An efficient heat pump can only deliver its full performance when its capacity, piping, electrical supply, supports, and clearances are properly planned. This approach results in a more reliable system that is easier to maintain and better suited to Quebec winters.