Installation of a Fujitsu AIRSTAGE Aquila XLTH dual-zone heat pump in Boisbriand

A wall-mounted unit positioned at the top of a staircase to distribute comfort more effectively between levels

This Fujitsu AIRSTAGE Aquila XLTH dual-zone heat pump installation in Boisbriand illustrates a common challenge in multistory homes: finding a location capable of efficiently serving a circulation area without interfering with doors, the staircase, moldings, or the space available for furniture.

In the photo taken after the work, the Fujitsu indoor unit is installed in the upper part of the wall, immediately near a staircase and an interior door. The white casing blends discreetly with the light-colored walls, while its elevated position allows it to blow air toward the open area rather than directly at a piece of furniture or an area that is occupied continuously.

This placement choice seems simple once the work is complete. Yet it results from several checks: clearance from the ceiling, the presence of the door on the right, the wall structure, the routing of the lines, the airflow direction, access to the filters, and air circulation in the stairwell.

In a Boisbriand HVAC installation, transition areas such as landings, corridors, and stairwells can become strategic. When used effectively, they allow an indoor unit to distribute air to several rooms or levels. If poorly assessed, however, they can instead create temperature differences, discomfort near the staircase, or inaccurate readings of the ambient temperature.

Why a dual-zone heat pump was suitable for this property

A dual-zone heat pump connects two indoor units to a single outdoor unit. Each indoor unit serves a separate zone and can have its own temperature setting.

This configuration is particularly useful in homes where a single wall-mounted unit is not enough to distribute heating and cooling evenly.

In Boisbriand, common situations include:

• a main floor and an upper floor;
• a finished basement and a living area;
• a primary bedroom far from the living room;
• an addition to the original building;
• two areas separated by a staircase or corridor;
• rooms with different sun exposures.

In this project, the visible unit near the staircase forms one of the system’s two zones. Its position makes it possible to treat a specific area while taking advantage of the natural airflow around the landing.

The Fujitsu multi-zone system allows each indoor unit to be controlled independently. Occupants can therefore set a different temperature in each zone according to the time, occupancy, and preferences. However, Fujitsu documentation specifies that the system provides heating or cooling, but not both simultaneously in different zones.

The two units can have separate settings, but they must operate in a compatible mode. In winter, they heat; in summer, they cool.

At the top of a staircase: a useful but demanding location

The stairwell creates a natural movement of air between levels. Warm air tends to rise, while cooler air descends. Installing a unit near a staircase can therefore help circulate comfort, but its location must be chosen precisely.

A poorly oriented unit could:

• send air directly into the stairwell;
• create a draft for people passing through;
• create too great a temperature difference between levels;
• primarily measure air coming from another floor;
• leave some rooms without sufficient air supply.

In this installation in Boisbriand, the unit is mounted on a side wall rather than directly facing the steps. This allows the airflow to be directed toward the open area and adjacent spaces.

The mounting height also helps distribute air above the passageway. Occupants are not exposed to a direct stream of air at face level when using the stairs.

Precise integration between the ceiling and the door

The available wall space was limited by the ceiling, the corner on the right, and the door trim.

Before securing the unit, we had to check:

• the actual width of the casing;
• the opening of the front panel;
• the space required to remove the filters;
• the clearance above the air intake;
• the distance from the door frame;
• the route of the lines behind the wall;
• the possibility of carrying out future maintenance.

An indoor unit should not simply be centered based on the appearance of the wall. Its location must allow access to its components and maintain the required airflow.

The photo shows that the unit was positioned with open space on the right, despite its proximity to the corner. The door frame remains unobstructed, and the unit does not visually overlap the trim.

An interior finish without a long, visible line-set cover

One of the interesting features of this installation is the absence of long, visible sections of piping indoors. The unit appears to be connected directly through the wall, creating a more understated finish.

To achieve this result, the wall penetration behind the unit must be planned precisely. The passage must allow for routing:

• refrigerant lines;
• the insulation;
• the communication cable;
• condensate drainage;
• the connections required by the configuration.

A hole offset by a few centimeters may require adding a side pipe cover or create a bend that is too tight behind the casing.

We therefore aim to align the passage point with the outlets provided on the Fujitsu unit while avoiding studs, electrical wires, and other elements inside the wall.

Drainage in an area near a staircase

In cooling mode, the indoor unit removes moisture from the air. The water must then be discharged through a drain.

In an installation located at the top of a staircase, an indoor leak would be particularly problematic. Water could stain the wall, reach the trim, or create a slippery surface near the steps.

We therefore pay close attention to the drainage slope.

When drainage operates by gravity, the following must be avoided:

• reverse slopes;
• sagging in the pipe;
• compressed fittings;
• sections that are too horizontal;
• obstacles in the wall cavity.

The drain is tested before the work is completed to confirm that the water drains freely.

Comfort in a stairwell depends on more than BTUs

A common mistake is to choose the capacity of an indoor unit based solely on the approximate area of the level.

In a stairwell, the vertical movement of air changes the perceived load. Requirements depend in particular on:

• the total height of the stairwell;
• the opening between the floors;
• the roof insulation;
• the exposure of the windows;
• the location of the bedrooms;
• the presence of doors;
• the temperature maintained in the other zone.

An oversized unit may quickly reach its setpoint near the landing, then reduce its operation while some rooms remain too hot or too cold.

An undersized unit may run for a long time without compensating for air exchanges between levels.

At AirGreen, we therefore evaluate the zone as an architectural whole, rather than as a simple number of square feet.

The features of the Fujitsu Aquila XLTH dual-zone system

Several capacities and possible combinations

Fujitsu’s H Series documentation presents multi-zone outdoor units rated at 18,000, 24,000, 36,000, and 45,000 BTU/h. Depending on the condenser selected, the system can power two to five indoor units.

For a dual-zone application, the Fujitsu table lists several permitted combinations of wall-mounted units, including:

• 7,000 + 7,000 BTU;
• 7,000 + 9,000 BTU;
• 7,000 + 12,000 BTU;
• 7,000 + 15,000 BTU;
• 9,000 + 9,000 BTU;
• 9,000 + 12,000 BTU;
• 9,000 + 15,000 BTU;
• 12,000 + 12,000 BTU.

These associations confirm the units’ compatibility with the condenser. They do not replace an analysis of the thermal requirements.

Fujitsu specifies that its combination tables are not intended to select the system capacity and recommends its design software to validate H-series AIRSTAGE equipment.

Why the exact capacity cannot be determined from the photograph

The visible unit belongs to the Fujitsu AIRSTAGE range, but the photograph does not allow its capacity in BTUs to be confirmed with certainty.

Several indoor models share a very similar casing. To identify the exact capacity, you must consult:

• the model number;
• the nameplate;
• the estimate;
• the invoice;
• the project file;
• the authorized combination with the outdoor condenser.

It is preferable not to assign a capacity solely based on the unit's apparent width.

In a technical publication, this caution is important. A properly identified system inspires more confidence than a list of assumed specifications.

Cold-climate heating

Fujitsu documentation indicates that the CTEB versions of the Aquila series can operate in heating mode down to -26 °C and in cooling mode up to 50 °C.

This operating capacity is relevant for a property located in Boisbriand, on the North Shore, where winter temperatures can be very low.

However, the minimum operating temperature does not necessarily correspond to the full rated capacity. As the outdoor temperature decreases, output and efficiency may vary.

We must therefore check the available capacity at low temperatures and compare it with the home's heat losses.

The important factors include:

• the insulation;
• the airtightness;
• the number of windows;
• the volume;
• the heat exchange between floors;
• the simultaneous needs of both zones;
• the existing supplemental heating.

The variable-speed compressor

The Fujitsu system uses an inverter-driven compressor. This technology adjusts the compressor speed according to the demand from the indoor units.

In a two-zone configuration, the system can modulate its output when:

• only one zone is operating;
• both zones require little capacity;
• one zone is nearly at its setpoint;
• the load increases in the stairwell;
• the outdoor temperature changes.

This modulation helps limit sudden temperature fluctuations and certain short cycles.

For a stairwell landing, adaptable output is useful because needs change quickly when doors are opened, warm air rises, or the other level begins to require more heating.

Two independent zones, with the same operating mode

Each indoor unit can be set to a different temperature.

For example:

• the floor can be maintained at 21 °C;
• the ground floor can be set to 22 °C;
• a lightly occupied zone can receive a more moderate setpoint;
• the airflow can be adjusted according to the area.

The units nevertheless share the same outdoor condenser.

They therefore cannot heat and cool simultaneously. Fujitsu specifies that the system provides both functions, but not in opposite modes at the same time.

To prevent conflicts, we explain to the homeowner how to adjust both controls according to the season.

The connection capacity can reach 130%

Fujitsu multi-zone systems may allow a total indoor-unit capacity of up to 130 % of the outdoor unit's rated capacity, depending on the configuration.

The manufacturer nevertheless specifies that exceeding 100% does not increase the condenser's actual output.

This rule must be understood before choosing the two indoor units.

When both zones require their maximum capacity at the same time, the available output is divided between them.

A combination exceeding 100% may be suitable if the peak loads do not occur simultaneously. In a multilevel home, this can sometimes make sense, since the upper floor and ground floor do not always respond the same way to sunlight or outdoor temperatures.

The choice must nevertheless be validated with a load calculation, rather than based on a general rule.

Pay particular attention to airflow near the door

The door visible to the right of the unit had to remain free of any obstruction. The door leaf, trim, and occupants' movements must not interfere with the wall-mounted air conditioner.

The lower louver of the Fujitsu can direct air forward and downward. We must prevent a concentrated stream of air from reaching someone entering or leaving the room directly.

The louver setting allows the airflow to be adapted according to the season.

In cooling mode

Cool air tends to sink. It is generally advantageous to send it more horizontally so that it mixes before descending.

In heating mode

Warm air naturally rises. The louver can be directed farther downward to push heat into the occupied area.

Near a staircase, these settings strongly influence air distribution between levels.

Mistakes to avoid in a similar location

This installation in Boisbriand highlights several common mistakes:

1. Install the unit too close to the ceiling.
2. Block the panel with the wall angle.
3. Neglect the door opening.
4. Direct the airflow straight into the stairwell.
5. Choose the BTU rating based on floor area alone.
6. Forget about air exchange between the levels.
7. Create a backfall in the drain.
8. Install a combination not authorized by Fujitsu.
9. Make the filters difficult to remove.
10. Do not account for the simultaneous needs of both zones.

Maintaining the wall-mounted unit installed at the top of the staircase

The unit’s height facilitates air distribution, but it requires the use of a stable step ladder for maintenance.

The homeowner should:

• clean the filters regularly;
• keep the upper air intake clear;
• check for any water leakage;
• watch for unusual noises;
• keep the area in front of the unit clear;
• have the drainage inspected if an odor or leak appears.

Professional maintenance may include cleaning:

• the coil;
• the tangential fan;
• the condensate pan;
• the drain;
• the louvers;
• internal surfaces.

In a stairwell, dust can easily circulate between levels. A dirty filter reduces airflow and limits the unit’s ability to distribute comfort throughout the open area.

A discreet installation in a passageway

The project’s visual success rests on the simplicity of the integration.

The white casing blends with the walls and trim. No long indoor line-hide cover crosses the wall. The unit is positioned high enough not to obstruct passage and far enough from the door to remain accessible.

The space beneath the unit remains clear. Homeowners therefore retain the ability to furnish or decorate the wall without blocking the airflow.

This understated design is important in an entrance, corridor, or stairwell because the unit is visible every day. A properly aligned and proportioned installation integrates much better with the architecture.

The AirGreen approach to a multizone heat pump in Boisbriand

At AirGreen, we do not choose the location of a wall-mounted unit solely based on its proximity to the exterior wall.

We analyze:

• air circulation;
• the layout of the floors;
• door placement;
• ceiling height;
• the wall structure;
• drainage;
• the routing of the lines;
• future maintenance;
• the occupants’ comfort;
• the final appearance.

This approach allows us to complete installations tailored to each property in Boisbriand, the North Shore, Montreal, Laval, Longueuil, and the South Shore.

In this project, the Fujitsu AIRSTAGE Aquila XLTH dual-zone heat pump was integrated at the top of a staircase to treat a strategic area without encroaching on the door or walkway.

The elevated positioning, discreet finish, preserved access to the filters, and airflow direction all contribute to a lasting result.

An effective multizone installation relies on this combination of decisions: properly selected capacity, an authorized Fujitsu configuration, a clean technical layout, and a location that respects how the home is actually used.