A multizone heat pump installed above a passageway to better serve the adjacent rooms
At this property in Pointe-Calumet, our mandate was to improve the comfort of two areas of the home without adding two separate outdoor units or undertaking the installation of a central duct network. We therefore installed a Fujitsu AIRSTAGE Aquila XLTH dual-zone heat pump, a configuration in which two indoor units share a single outdoor unit.
The photograph shows one of the wall-mounted units installed in a circulation area, near a staircase and immediately beside the opening leading to another room. This location is particularly interesting from a technical standpoint. It is not a large, completely unobstructed wall, but rather a limited section bordered by the ceiling, the wooden door frame, the stair railing, and several elements already in place.
In this type of project, the challenge is not simply to find a place where the unit can be mounted. It is necessary to select a location that allows the airflow to circulate, remains accessible for maintenance, and fits into the home's movement patterns.
The result achieved in Pointe-Calumet clearly illustrates our approach: making smart use of a section of wall that is difficult to utilize while directing heating and cooling toward a strategic area of the home.
Why the passageway near the staircase was a suitable location
In several homes, the staircase acts as a natural corridor for air movement. Warm air rises toward the upper floor, while cooled air tends to descend. The location of a wall-mounted unit near this vertical airflow must therefore be analyzed carefully.
Installed above the passageway, the Fujitsu unit can distribute air toward the space in front of it without occupying a main wall intended for furniture. Its location also helps limit obstacles directly beneath the airflow.
Before settling on such a position, we assess in particular:
- the available wall width;
- the distance between the unit and the ceiling;
- the proximity of the door frame;
- the clearance needed to open the panel;
- the position of the stair railing;
- the direction of the airflow;
- the occupants' daily circulation;
- the route of the refrigerant lines and drain.
The photo shows that the cabinet is installed very high, but that space remains above the unit to allow air intake. The lower flap can also open without touching the door trim.
An installation that respects the existing elements
The wall already had several elements to work around. Notably, a ceiling detector, wall-mounted equipment beneath the unit, and wooden door trim on the right can be seen.
These components influence the final positioning. We must avoid covering a detector, making a control inaccessible, or placing the heat pump where it would interfere with opening a door.
The distance between the unit and the trim was used tightly but functionally. The heat pump occupies the upper part of the wall without encroaching on the door or the railing.
In a residential HVAC installation, this detail matters just as much as the choice of equipment. A poorly positioned unit can complicate maintenance, create an unpleasant draft, or make it seem as though it was added without regard for the architecture.
A visible but contained side connection
On the left side of the unit, a small service passage can be seen. This generally allows the necessary components between the indoor and outdoor units to be grouped together:
- refrigerant lines;
- insulation;
- communication wiring;
- condensate drain;
- finishing elements.
In an existing building, it is not always possible to run all the lines directly behind the unit. The presence of studs, masonry, another room, or an exterior obstruction may require a side exit.
Our goal was therefore to keep the route short, protected, and visually orderly. An overly bulky finish would have reduced the already limited space between the unit and the side wall. The chosen route therefore remains discreet in relation to the site's layout.
Why a dual-zone heat pump was preferable to two separate systems
A home with two areas that are difficult to heat or cool could be equipped with two independent heat pumps. However, this solution would require two outdoor units, two electrical supplies, and more space around the building.
The Fujitsu dual-zone configuration is instead designed to connect two indoor units to a single outdoor compressor.
The main advantages are as follows:
- reducing the number of outdoor units;
- separate control of the two zones;
- adapting the indoor capacity to each room;
- heating and cooling with the same equipment;
- capacity modulation according to demand;
- installation without a central duct network.
Each indoor unit has its own controller. Occupants can therefore set two different temperatures, depending on the use and exposure of each zone.
Fujitsu documentation states that AIRSTAGE multi-zone systems allow each indoor unit to be controlled independently. It also indicates that a single outdoor unit can serve several types of indoor units, including wall-mounted models, Slim Duct units, compact cassettes, and certain ducted units.
One important limitation: both zones share the same mode
Independent control does not mean that each unit can simultaneously select an opposite mode.
The system can heat or cool both zones, but it generally cannot heat one zone while the other is actively cooling. Fujitsu specifies that its systems provide heating and cooling without producing both modes simultaneously.
The set temperatures can nevertheless be different. For example, one zone can be set to 21 °C and the other to 19 °C in heating mode. One unit can also be turned off while the other is operating.
In a residence, this limitation rarely causes problems during a typical season. However, it must be explained before installation so that occupants understand how the multi-zone system actually operates.
Choosing the indoor unit capacity
The photograph does not show the complete model number or confirm the exact capacity of the visible unit. Several Fujitsu wall-mounted units have similarly sized cabinets.
We therefore never determine BTUs based on appearance alone.
The required capacity depends in particular on:
- the area of the zone;
- ceiling height;
- the number of windows;
- sun exposure;
- the quality of the insulation;
- the building’s airtightness;
- the room’s location;
- heat loss;
- the number of occupants;
- the actual use of the space.
A unit installed near a staircase can influence several areas. However, you should not assume that a unit placed in a passageway will automatically heat all enclosed rooms evenly.
Air circulates mainly through open spaces. A bedroom whose door remains closed may require its own indoor unit, which explains why a dual-zone configuration is relevant for this project.
Fujitsu-approved combinations for a dual-zone installation
The Fujitsu Aquila series allows several combinations of outdoor and indoor units. The documentation specifically lists 18,000, 24,000, 36,000, and 45,000 BTU/h outdoor units.
The 18,000 BTU/h outdoor model designed for two indoor units accepts, among others, the following combinations:
- 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 combinations are authorized by the manufacturer, but they are not a universal recommendation. Fujitsu also states that its tables are not intended to be used alone to select the system capacity. The manufacturer recommends using its Design Simulator software to validate the AIRSTAGE H series configuration.
When the total capacity of the indoor units exceeds the outdoor capacity
A multizone system can sometimes support a total indoor capacity greater than the outdoor unit’s nominal capacity.
For example, an 18,000 BTU/h outdoor unit can, in certain approved combinations, be connected to two indoor units totaling 21,000 or 24,000 BTU/h.
This capability does not turn the compressor into a higher-capacity unit. Fujitsu specifies that exceeding 100% in a combination does not increase the system’s total output.
When both zones require a lot of power at the same time, the available capacity is shared.
This approach can be relevant when the two rooms do not reach their maximum load simultaneously. For example, a west-facing zone may be more demanding in the late afternoon, while a bedroom requires more comfort at night.
A system designed for the winters in the Montreal region
In Pointe-Calumet, choosing a heat pump must take winter temperatures and wind exposure into account. The proximity of the lake and more open spaces can intensify the sensation of cold and heat loss in some properties.
Fujitsu documentation indicates that Aquila CTEB models designed for cold climates can operate in heating mode down to -26 °C. It also mentions cooling operation up to 50 °C.
However, a minimum operating temperature does not mean that the appliance provides its full rated capacity at that temperature. A heat pump's performance varies according to outdoor conditions.
To assess its role during the winter, we analyze:
- available capacity at low temperatures;
- the home's heating load;
- wall and roof insulation;
- window quality;
- air infiltration;
- the presence of baseboard heaters or other supplemental heating;
- the needs of each zone.
A low-temperature heat pump can significantly reduce the use of existing electric heating, but the system must be selected based on the actual house.
Installation details that protect performance and simplify maintenance
Air circulation in a transitional space
The visible unit is installed near a passageway and staircase. This type of location can promote air movement toward several areas, but requires precise louver adjustment.
In cooling mode, cool air must be projected far enough so that it does not immediately descend into the staircase. In heating mode, the orientation should promote the return of warm air toward the occupied area instead of allowing it to accumulate at the ceiling.
When commissioning the system, we therefore check:
- louver opening;
- jet direction;
- fan speed;
- the presence of obstacles;
- air movement near the door;
- distribution toward the staircase and adjacent rooms.
Automatic louver adjustment may be suitable in many situations, but a fixed orientation can sometimes provide greater comfort depending on the layout of the house.
The importance of upper clearance
Ambient air enters the unit primarily through the top. Even when the appliance is installed near the ceiling, sufficient clearance must be maintained.
Excessively limited space could:
- reduce airflow;
- increase noise;
- reduce effective capacity;
- accelerate filter fouling;
- make it harder to open the panel.
In the photo, the unit is installed in the upper part of the wall, but it does not appear to be wedged against the ceiling. This positioning preserves airflow intake while keeping the lower passage clear.
The condensate drain
In cooling mode, the unit removes moisture from the air. This water is collected in an internal pan and discharged through a drain.
The drain must be installed with sufficient slope whenever gravity drainage is possible. A rise, crushed pipe, or improper fastening can cause backflow.
Possible consequences include:
- water leak;
- marks on the wall;
- odors;
- gurgling noise;
- drain pan overflow;
- unit shutdown;
- damage to surrounding materials.
In a space adjacent to a wooden staircase, leak protection is particularly important. A small amount of repeated water exposure can damage paint, trim, or wooden components.
Preparing the refrigerant circuit
Each indoor unit of a dual-zone heat pump is connected to the outdoor unit by a separate circuit.
The connection generally includes:
- a liquid line;
- a gas line;
- continuous insulation;
- a communication cable;
- a drain.
The copper lines must be cut, flared, and tightened precisely. A minor leak may not be visible on the day of installation but can gradually reduce performance.
Symptoms of a refrigerant leak may include:
- insufficient heating;
- weak cooling;
- very long cycles;
- ice formation;
- unusual noise;
- higher energy consumption;
- error codes.
We therefore perform leak checks and evacuation before commissioning.
Variable-speed operation
Inverter technology allows the compressor to adjust its output to the demand of both zones.
As temperatures approach the setpoints, the system may reduce its output instead of shutting down completely. This modulation helps maintain more stable comfort and reduce frequent on-and-off cycling.
Fujitsu documentation also mentions:
- a blue-fin outdoor heat exchanger for improved corrosion resistance;
- circuit protection;
- fan motor protection;
- compressor protection.
These features support equipment reliability, but they do not replace proper installation or regular maintenance.
Mistakes to avoid in a similar installation
Assuming that one unit in the hallway will always replace two zones
Air does not move efficiently through several closed doors. A second indoor unit is often still necessary for a bedroom or an isolated floor.
Positioning the unit too close to the ceiling
Insufficient space can reduce airflow intake and make filter maintenance more difficult.
Directing the airflow straight into the stairwell
The air could leave the area you are trying to heat or cool too quickly.
Blocking access with the framing or railing
The front panel must be able to open, and the filters must remain accessible.
Choosing BTUs using a quick formula
Surface area alone does not account for insulation, windows, wind, or the differences between the two zones.
Confusing interior capacity with exterior capacity
An indoor combination exceeding 100% does not automatically produce more heating or cooling.
Wall-mounted unit maintenance
The unit is installed high above a traffic area. Stable access must therefore be provided for filter cleaning.
Routine maintenance includes:
- removing and cleaning the filters;
- checking the airflow;
- checking for any water leakage;
- checking the upper clearance;
- monitoring for unusual noises;
- gentle cleaning of the cabinet.
Professional HVAC maintenance allows for more thorough cleaning of the heat exchanger, tangential fan, drain pan, and drain.
A clean filter does not guarantee that the inside of the unit is completely free of dust. Over time, the blower wheel can become dirty and lose some of its airflow.
Eligibility for financial assistance
The photograph and the Aquila XLTH name are not enough to confirm a subsidy amount.
Eligibility usually depends on:
- of the complete outdoor model;
- of the two indoor units’ models;
- of the combination’s AHRI number;
- of the capacity recognized at the requested temperature;
- of the building;
- of the installation date;
- of the documents provided;
- of the program rules in effect.
We therefore verify the exact combination before presenting potential financial assistance. This step prevents confusing the eligibility of a series with that of a specific assembly.
An installation designed for the actual building
This project in Pointe-Calumet shows how a Fujitsu AIRSTAGE Aquila XLTH dual-zone heat pump can be integrated into a restricted location without sacrificing circulation or accessibility.
The indoor unit was placed above a passageway, near the staircase and a door frame. This choice makes effective use of an available section of wall while allowing the airflow to reach a central area of the home.
For the homeowner, the dual-zone configuration provides more precise control of two spaces with a single outdoor unit. For us, the work involved coordinating capacity, airflow, drainage, line routing, and future maintenance.
At AirGreen, we install heat pumps, wall-mounted air conditioners, and multi-zone systems in Montreal, Laval, Longueuil, on the North Shore, and on the South Shore. Each project is adapted to the building’s constraints, whether it involves a narrow wall, a staircase, a door, a masonry façade, or a complex technical route.