A high wall-mounted installation to better manage air circulation between two levels
In this residence in Longueuil, we installed a Fujitsu AIRSTAGE Aquila XLTH dual-zone heat pump to improve comfort in two distinct areas of the home using a single outdoor unit. The selected configuration makes it possible to heat and cool two zones independently, without adding two outdoor compressors and without modifying the building to integrate a central duct network.
The photograph shows one of the indoor units installed in a vertical space, immediately adjacent to a staircase and a wooden railing. This detail is far from insignificant. In a multi-level home, the staircase naturally becomes an important axis for air circulation. Warm air tends to rise, while cooled air descends. The positioning of a wall-mounted air conditioner or heat pump near a staircase must therefore be carefully planned to prevent the generated air from leaving too quickly the area we actually want to treat.
The Fujitsu unit was installed near the ceiling, in a corner where the wall meets a taller vertical section. It is located above the railing, in a space that would have been difficult to use otherwise. This position keeps the main wall clear, limits obstruction in the passageway, and directs the airflow toward the home’s open volume.
An unusual location that required precise planning
The installation shown in the photo presents several simultaneous constraints:
- a high wall;
- more difficult access than in a standard room;
- the presence of a stair railing;
- a ceiling close to the top of the unit;
- an architectural corner that limits movement;
- a small visible technical finish beneath the unit;
- a passageway located directly below the work area.
Before mounting the wall bracket, we must always check the strength of the support, the level of the unit, the required clearances, and the route of the lines. In this case, access at height was also a safety concern. An installation near a staircase cannot be carried out in the same way as an installation on a clear wall on the ground floor. The work equipment, technicians’ positioning, and protection of the surrounding surfaces must be adapted to the location.
We also had to ensure that the unit would remain accessible after the work was completed. A location may seem ideal at the time of installation but become problematic if the homeowner cannot remove the filters or if a technician cannot open the front panel during future HVAC maintenance.
The heat pump was therefore positioned high enough to take advantage of the available space while maintaining functional clearance and allowing the lower flap to open fully.
Why a dual-zone heat pump was suitable for this Longueuil home
A dual-zone heat pump connects two indoor units to a single outdoor unit. Each indoor unit has its own controls, set temperature, and ventilation settings.
This solution is well suited when two areas of the home have different needs, for example:
- an upper floor that is warmer in summer;
- a ground floor whose temperature remains more stable;
- a bedroom and an open-plan area;
- an office and a living room;
- a rear extension and the main section of the building;
- two zones separated by a staircase or hallway.
In this installation in Longueuil, the presence of the staircase suggests a significant difference in elevation. A single unit installed at the bottom or top of the stairwell would not necessarily have been enough to precisely control both spaces. Instead, the dual-zone system makes it possible to assign one indoor unit to each area according to its actual load.
Fujitsu documentation indicates that H Series AIRSTAGE multi-zone systems can power multiple indoor units from a single outdoor unit. Each indoor unit can be controlled separately, and several formats are compatible, including wall-mounted units, Slim Duct models, compact cassettes, and certain ducted units.
Separate controls, but a shared operating mode
Independent control of the two units allows the homeowner to set a different temperature in each zone. For example, one room can be maintained at 21 °C while the other is set to 19 °C.
It is also possible to turn off one unit when its zone is not in use while leaving the second one running.
However, it is important to understand how a multi-zone system works: the two units share the same outdoor unit and generally must operate in the same main mode.
In other words, the system can:
- heat both zones;
- cool both zones;
- operate only one of the two units;
- maintain different setpoint temperatures.
However, it cannot actively heat one zone while the other simultaneously calls for cooling. Fujitsu documentation specifies that the system provides heating and cooling, but not both at the same time.
This feature is important in a multilevel home. During the shoulder seasons, the upper floor may be warmed by the sun while the ground floor remains cooler. In this case, a consistent shared mode must be selected, or another heating source must be used temporarily in the area that needs it.
The photo shows a technical finish under the unit
Under the right side of the unit, a small white rectangular box can be seen. The photograph alone does not make it possible to identify its exact function with certainty. It may be an element associated with the passage of the lines, drainage, or an auxiliary component required in this configuration.
This detail reveals the constraints encountered in existing buildings. When the unit is installed very high up or near a staircase, it is not always possible to use a simple horizontal route with a natural slope toward the outside.
The technical route must therefore be adapted to:
- the wall structure;
- the position of the studs;
- the presence of another floor;
- the location of the outdoor unit;
- the slope required for the drain;
- future accessibility;
- the interior appearance.
When we need to integrate a visible component, we aim to minimize its size and place it near the unit. The finish must remain clean, but also removable when maintenance or inspection is required.
The challenge of drainage in a high-level installation
In cooling mode, the indoor unit removes some of the moisture contained in the air. This moisture condenses on the coil, then flows into an internal tray before being discharged.
The drain is therefore an essential part of the HVAC installation.
In a typical installation on an exterior wall, it is often possible to create a continuous slope toward the outside. In a stairwell or on an interior wall, the route may be more complex.
We check in particular:
- the available slope;
- the drain’s total length;
- changes in direction;
- the risk of backflow;
- pipe fastening;
- the absence of crushing;
- the outlet point;
- the ability to inspect or clean the system.
A poorly designed drain can cause:
- water running down the wall;
- marks on the ceiling or in the stairwell;
- a gurgling noise;
- an accumulation in the tray;
- odors;
- a safety shutdown;
- damage to the finishes and wood.
The proximity of the railing made this check particularly important. A recurring leak could damage not only the paint but also the wooden elements beneath the unit.
The importance of airflow in a stairwell
The staircase acts as an open duct between levels. This natural airflow can be useful, but it can also reduce the effectiveness of a poorly oriented unit.
In cooling mode, if the louver directs the air too strongly downward, cool air may quickly descend into the stairwell instead of remaining in the upper area. In heating mode, warm air may rise and accumulate near the ceiling if the airflow is not directed toward the occupied area.
During commissioning, we therefore check:
- the position of the vertical louver;
- the lateral direction of the airflow;
- the fan speed;
- the jet's reach;
- the air's response near the railing;
- the temperature achieved in neighboring areas.
In some cases, automatic swing is perfectly suitable. In others, a fixed position or a lower speed provides greater comfort.
An efficient system is not merely one that can produce enough heat or cooling. It must also distribute that energy where it is actually needed.
Choosing the capacity in BTUs
The complete model number is not legible in the photo. It is therefore not possible to confirm the exact capacity of the visible indoor unit based solely on its appearance.
Several Fujitsu models share a similar cabinet. A 7,000, 9,000, 12,000, or 15,000 BTU/h unit can sometimes be difficult to distinguish visually.
To select the capacity, we consider:
- the area and volume of the zone;
- the ceiling height;
- the presence of an open stairwell;
- the amount of glazing;
- solar exposure;
- the floor;
- exterior walls;
- insulation;
- the airtightness;
- the number of occupants;
- how the space is used;
- the capacity of the second indoor unit.
A stairwell increases the air volume connected to the unit. A simple square-footage calculation is therefore insufficient. A unit selected solely according to floor area could be too small for the actual volume it affects.
Conversely, an oversized unit could reach its setpoint too quickly, reduce dehumidification, and create short cycles.
Permitted combinations for the Fujitsu Aquila
The Fujitsu AIRSTAGE Aquila series supports several indoor-unit configurations. The documentation presents 18,000, 24,000, 36,000, and 45,000 BTU/h outdoor units, which can power two to five units depending on the selected model.
For an 18,000 BTU/h outdoor unit designed for two zones, the approved combinations include:
- 7,000 + 7,000 BTU/h;
- 7,000 + 9,000 BTU/h;
- 7,000 + 12,000 BTU/h;
- 7,000 + 15,000 BTU/h;
- 9,000 + 9,000 BTU/h;
- 9,000 + 12,000 BTU/h;
- 9,000 + 15,000 BTU/h;
- 12,000 + 12,000 BTU/h.
These tables confirm technical compatibility, but they do not replace a selection based on the building's needs. Fujitsu specifies that its Design Simulator software should be used to properly select AIRSTAGE H series equipment.
Why the total indoor unit capacity can exceed the outdoor capacity
Some approved combinations have a higher total indoor capacity than the outdoor unit.
For example, an 18,000 BTU/h outdoor unit can be connected to two indoor units totaling 21,000, 22,000, or 24,000 BTU/h, depending on the approved combinations.
This possibility is based on the fact that the two zones do not always require their full capacity at the same time.
In a two-story home:
- the upper floor may require more cooling in the afternoon;
- the ground floor may require more heating in the morning;
- a bedroom may be lightly used during the day;
- an open-concept area may become the priority when occupied.
However, an incorrect interpretation should be avoided: higher indoor capacity does not create additional outdoor capacity. Fujitsu clearly states that exceeding 100% in a combination does not increase the system's production capacity.
When both zones call for their maximum output simultaneously, the available capacity must be distributed.
A low-temperature solution suited to the climate of Longueuil and the South Shore
Heating operation down to -26 °C for cold-climate models
Cold-weather heating capacity is a major criterion for a heat pump installed in Longueuil. Winter temperatures can fall below -20 °C, and windy periods increase building heat losses.
Fujitsu documentation indicates that Aquila CTEB cold-climate models can operate in heating mode down to -26 °C. It also mentions cooling operation up to 50 °C.
This data represents an operating range and does not mean that the unit will maintain its full rated capacity at -26 °C. Like all heat pumps, its capacity and efficiency vary with the outdoor temperature.
Therefore, we must consider:
- the capacity available at low temperatures;
- the home's thermal losses;
- window quality;
- insulation;
- exposure to wind;
- the open volume of the stairwell;
- the existing heating system;
- the desired indoor temperature.
A low-temperature heat pump can significantly reduce the use of electric baseboard heaters or another backup system. However, the decision to use it as the main or supplemental heating system should be based on a complete analysis of the building.
Variable-speed compressor modulation
The Fujitsu system uses an inverter-driven compressor. It adjusts its speed according to the combined demand of both zones.
When the home is far from the desired temperature, the compressor can increase its output. As the rooms approach their setpoint, it can reduce its operation instead of shutting down completely.
This modulation helps to:
- maintain a more stable temperature;
- limit frequent starts;
- improve comfort;
- match consumption to the load;
- reduce significant fluctuations;
- better meet the changing needs of both zones.
Fujitsu documentation also mentions blue-coated heat exchanger fins to improve corrosion resistance, as well as built-in protection for the circuits, fan motor, and compressor.
Checks performed during commissioning
A multi-zone installation cannot be validated simply by confirming that both units start.
We check in particular:
- the tightness of the refrigerant connections;
- the quality of the vacuum;
- the operation of each indoor unit;
- communication between the units;
- condensate drainage;
- the response of the remote controls;
- the movement of the louvers;
- the fan speed;
- the absence of abnormal vibration;
- air distribution in each zone.
In a space near a staircase, we also observe how air moves between levels. The initial settings can then be adjusted according to how the home is used.
Mistakes to avoid when installing a unit at height
Installing the unit without planning for maintenance
The filters must be removable, and the front panel must remain accessible.
Directing all airflow toward the stairwell
The main area may receive too little heating or cooling.
Reducing the upper clearance excessively
Air enters through the top of the unit. Insufficient clearance can reduce airflow.
Choosing capacity based solely on floor area
In a space open to a staircase, the actual air volume is greater than that of an enclosed room.
Neglecting the drain
A leak at height can damage a large section of wall and the wooden elements located below.
Confusing individual control with opposite modes
The two units have separate settings but share the same heating or cooling mode.
Maintenance required for this wall-mounted unit
The unit is installed very high. The homeowner must therefore use a stable and safe means of access to clean the filters.
Routine maintenance includes:
- cleaning the filters;
- checking the airflow;
- checking the drain;
- monitoring unusual noises;
- keeping the top of the unit clear;
- gentle cleaning of the cabinet.
Professional HVAC maintenance also makes it possible to clean the fan wheel, heat exchanger, condensate pan, and drain.
Even with clean filters, deposits can accumulate on the tangential fan. This reduces airflow and can cause an imbalance or vibration.
Eligibility for a subsidy
The name Fujitsu Aquila XLTH is not sufficient to confirm eligibility for financial assistance. The exact combination must be validated using the complete models and the applicable AHRI number.
Verification may require:
- the outdoor unit model;
- the models of both indoor units;
- the certified combination;
- the recognized low-temperature capacity;
- the installation address;
- the detailed invoice;
- the documents requested by the program;
- the rules in effect on the project date.
Since the nameplate is not legible in the photo, no precise amount can be attributed based on the image alone.
An installation adapted to the home’s actual architecture
This Longueuil project demonstrates that a multi-zone heat pump must be designed around the building, not merely the model selected.
The Fujitsu indoor unit was installed in a vertical space near a staircase, with a high wall and unusual access. We used this configuration to clear the main surfaces, promote air circulation, and maintain a visually clean result.
The homeowner now benefits from a Fujitsu AIRSTAGE Aquila XLTH dual-zone heat pump capable of serving two areas with a single outdoor unit. The system offers individual temperature control, capacity modulation, and heating capacity suited to cold conditions.
At AirGreen, we install wall-mounted heat pumps, multi-zone systems, and HVAC solutions in Montreal, Laval, Longueuil, the North Shore, and the South Shore. We adapt each project to the dimensions, architecture, heat loss, drainage, electrical requirements, and future access for maintenance.