Installation of a Fujitsu AIRSTAGE Altair 500 wall-mounted heat pump in McMasterville on the South Shore

A flat-roof installation that requires much more than simply connecting a heat pump

At McMasterville, installing this Fujitsu AIRSTAGE Altair 500 wall-mounted heat pump led us to work in a configuration very different from a conventional ground-level residential installation. Here, the outdoor unit was installed on a flat roof, on a carefully prepared raised structure designed to keep the equipment above the roof surface while maintaining the necessary clearances around the heat exchanger.

The site photo immediately shows the elements that make this project interesting: a Fujitsu outdoor unit placed on a metal support, heavily insulated refrigerant lines, a membrane roof, wooden structural elements used to distribute the loads, and a layout that takes technical access into account.

For us, this type of installation never simply means “placing the machine on the roof.” Stability, drainage, snow, ice, vibrations, airflow, exposure to sunlight and the elements, as well as future access for HVAC maintenance, must all be considered before commissioning.

Why install the outdoor unit on a flat roof in McMasterville?

In some properties in McMasterville and the South Shore, the available space around the building does not necessarily provide a suitable location for a heat pump.

Several constraints may lead to choosing a rooftop installation:

• limited ground space;
• a narrow driveway or passageway;
• a terrace occupying the rear façade;
• the need to preserve a yard;
• the distance between the indoor unit and a suitable outdoor location;
• the desire to move the equipment away from the main traffic areas;
• the specific configuration of a multi-unit residential building.

For this project, the roof provided a usable area where a structured and accessible outdoor installation could be created. However, the roof also requires our technicians to approach the equipment support differently.

A raised support to prevent direct contact with the roof

In the photo, the Fujitsu AIRSTAGE Altair 500 outdoor unit does not rest directly on the membrane.

We have a raised metal structure installed on load-distributing support elements. This configuration offers several practical advantages.

First, the equipment remains clear of the roof surface. During rain, snowmelt, or the heat pump’s defrost cycles, water can therefore flow beneath the structure instead of becoming trapped immediately around the cabinet base.

Second, this additional height becomes particularly useful in winter. A heat pump must be able to draw in and discharge air properly, even when snow accumulates around the building.

Third, the structure makes servicing easier. A technician can access the connections and components more easily than with a unit placed practically at membrane level.

Distributing loads without damaging a roof membrane

Installing an outdoor unit on a roof also requires considering what lies under the heat pump.

A roof membrane is not a concrete slab. Narrow metal feet or poorly positioned supports can concentrate a significant load on a small surface.

In this installation, wooden crosspieces can be seen serving as the base of the structure. The purpose of this type of configuration is to provide a stable seat and distribute the load over a larger surface.

For projects similar to those in Montréal, Longueuil, and the South Shore, we always assess the existing configuration before installing equipment on a roof. Considerations may include the building structure, the type of membrane, drainage slopes, and elements already present on the roof.

A unit that is perfectly operational from a refrigeration standpoint can still be a poor installation if its support gradually damages the roofing system.

Vibrations deserve particular attention on a roof

Another challenge with rooftop installations involves vibrations.

The compressor and outdoor fan run for long periods. Even a relatively quiet heat pump can transmit mechanical vibration to a structure if it is mounted too rigidly or if its base is not properly stabilized.

In a residential building, this transmission can sometimes become noticeable indoors as a humming sound.

We therefore seek to create a solid, level base suited to the equipment. The quality of the HVAC installation directly affects acoustic comfort here, even if the outdoor unit is physically far from the occupants.

Refrigerant lines: a highly visible detail in this installation

The photo clearly shows the lines connecting the outdoor unit to the rest of the system.

They are protected by thick black insulation and an exterior coating designed to preserve the entire assembly in an exposed environment. On a roof, this protection is particularly important because the lines are directly subjected to:

• solar radiation;
• rain;
• snow;
• freeze-thaw cycles;
• temperature fluctuations;
• the mechanical stresses associated with the piping route.

Degraded insulation is not merely an aesthetic problem. It can reduce the circuit's thermal efficiency and promote condensation in certain areas.

We therefore pay particular attention to the fittings, bends, and sections where the line changes direction.

A refrigerant line bend must never be forced

In this installation, the piping follows a smooth route before reaching the outdoor unit.

This is an important detail. The copper tubing used in a heat pump must not be crushed, pinched, or bent with too tight a radius. A restriction in a refrigerant line can affect refrigerant flow and system performance.

We aim to maintain gradual curves and reduce mechanical stress on the connections.

Raising the unit also provides more space to manage this transition properly.

Why the Fujitsu AIRSTAGE Altair 500 is suitable for this type of installation on the South Shore

A single-zone range available in several capacities

The Fujitsu AIRSTAGE Altair 500 belongs to Fujitsu's H series and includes several single-zone systems: 09KPAS1, 12KPAS1, 18KPAS1, 24KPAS1, 30KPAS1, and 36KPAS1.

According to the Fujitsu technical specifications, rated cooling capacities range from 9,000 to 33,000 BTU/h, while rated heating capacities range from 10,000 to 34,000 BTU/h, depending on the model. The range uses R-32 refrigerant and Inverter technology.

The exterior photograph does not show the rating plate clearly enough to determine with certainty the capacity installed in McMasterville. We therefore prefer not to arbitrarily assign a BTU rating to the project.

In practice, we always choose the capacity based on the building's needs rather than the apparent size of the outdoor unit.

Efficiency varies by model

The Altair 500 technical specifications list VERY2 efficiency ratings ranging from 21.0 to 26.0, depending on capacity.

The values listed are:

• 26.0 for the 09KPAS1;
• 24.0 for the 12KPAS1;
• 22.0 for the 18KPAS1;
• 21.5 for the 24KPAS1;
• 22.0 for the 30KPAS1;
• 21.0 for the 36KPAS1.

However, a project's actual performance does not depend solely on the manufacturer's specifications. Piping length, sizing, vacuum quality, refrigerant charge when required, and airflow all influence the performance achieved once the system is installed.

R-32 and the new generation of Fujitsu equipment

The Altair 500 operates with R-32.

In its documentation, Fujitsu compares a global warming potential of 675 for R-32 with 2,088 for R-410A, representing a 68% reduction according to the manufacturer’s data.

For our installations in McMasterville, Longueuil, Montréal, Laval, on the North Shore and the South Shore, this refrigerant change also means that we must follow the procedures specified for the new generation of systems.

Replacing an old heat pump therefore does not automatically mean that the entire existing circuit can be kept without verification.

Pipe dimensions depend on capacity

The Altair 500 lineup uses different refrigerant line sizes.

According to Fujitsu:

• the 9,000 and 12,000 BTU models use a liquid line of 1/4 po and a gas line of 3/8 po;
• the 18,000 and 24KPAS1 models use 1/4 in. liquid and 1/2 in. gas;
• the 30KPAS1 and 36KPAS1 models use 3/8 in. liquid and 5/8 in. gas.

This detail is particularly important when a customer wants to keep the piping from an old unit.

We always verify the actual size before confirming reuse. A pipe that appears to be in good condition may still be incompatible with the new heat pump.

A practical piping length for a rooftop installation

A rooftop installation can create a longer route than when an outdoor unit is installed immediately behind the indoor unit.

The Altair 500 series offers valuable flexibility in this regard.

Depending on the capacity, Fujitsu allows maximum piping lengths ranging from 66 feet to 164 feet, with maximum vertical differences ranging from 49 to 98 feet.

This margin can be particularly useful in buildings where the indoor unit is located several floors below the roof.

However, an authorized maximum length does not mean that we should systematically use the entire distance. The simpler, cleaner, and more properly sized the route, the better we can control the installation.

Inverter technology: adapting operation to the building’s needs

The Altair 500’s Inverter compressor allows the heat pump to modulate its capacity according to demand.

This means that the system does not need to operate constantly at maximum capacity. As the indoor temperature approaches the setpoint, the unit can reduce its operating level.

This modulation promotes:

• more consistent comfort;
• smaller temperature variations;
• generally quieter operation;
• consumption better suited to the actual thermal load.

However, proper sizing remains essential. Inverter technology does not replace a proper analysis of the building’s needs.

Heating down to -15 °C according to the published range

Fujitsu indicates a heating operating range down to -15 °C for this product line.

This information must be interpreted correctly: a minimum operating temperature does not necessarily mean that the heat pump retains all of its rated capacity at that temperature.

In a region such as McMasterville, we take winter conditions and the existing heating system into account before presenting a heat pump as a primary or supplementary solution.

Fujitsu documentation also mentions certain special functions depending on the model, but these must always be associated with the specific model installed.

The compact outdoor unit makes certain installations easier

In the McMasterville photo, we can clearly see how the relatively compact shape of the outdoor unit makes it possible to maintain clearance around the equipment despite the other elements on the roof.

Notably, there is a brick building structure, nearby ventilation equipment, and various rooftop elements.

In this type of situation, we must avoid placing a heat pump too close to an obstacle that could block its coil or cause the discharged air to recirculate.

The outdoor fan must be able to move a large volume of air. Poor placement can reduce performance even when every other part of the installation is technically correct.

Service access must be considered from day one

One of the mistakes we sometimes encounter in older installations is a unit placed where no one can actually work around it.

This becomes particularly problematic on a roof.

Our technicians must be able to access:

• to the service valves;
• to the electrical panel;
• to the compressor;
• to the fan;
• to the refrigerant connections;
• to the coil.

An installer may save a few minutes by squeezing a unit into a confined space, but this choice can make every service call more difficult in the years that follow.

In McMasterville, the outdoor unit remains installed on an open structure that provides reasonable access around the equipment.

Snow and defrosting: two reasons not to place the unit directly on the roof

During a heating period, the outdoor unit of a heat pump naturally accumulates frost on its coil. The system periodically performs a defrost cycle to remove this buildup.

The water produced must be able to drain freely away from the base of the unit.

On a flat roof, this point deserves particular attention. If the unit is installed too low, water can freeze immediately around its base and gradually create a mass of ice.

By raising the unit, we improve the space available beneath the cabinet for drainage and reduce the risk of snow accumulation quickly blocking the lower part of the appliance.

A clean installation should also remain clean after several winters.

The job is not finished when the system is started up for the first time.

To maintain the performance of the Fujitsu Altair 500, we recommend keeping the outdoor unit free of debris and periodically inspecting the area around the heat exchanger.

On a roof, this notably means checking for leaves, snow, and ice accumulation around the unit.

Regular HVAC maintenance also makes it possible to check the condition of the line insulation, supports, connections, and outdoor heat exchanger.

Energy Star and financial assistance: the specific model remains decisive

The Fujitsu specifications associate several Altair 500 models with different ENERGY STAR classifications, including designations related to cold climates depending on capacity.

However, this is not enough to guarantee a specific subsidy amount.

For a financial assistance application, we must verify the exact combination of indoor and outdoor units and the program conditions applicable at the time of installation.

We always prefer to confirm eligibility using official references rather than estimating a subsidy solely based on the name “Altair 500.”

This McMasterville project summarizes our approach to complex installations well.

This installation is interesting because the most important part of the work is directly visible in the photo.

The heat pump is not simply placed on a roof. It is installed on a raised structure, with carefully managed lines and positioning that takes the roof, access, and the unit’s immediate surroundings into account.

This is exactly what we strive for at AirGreen in our wall-mounted heat pump projects in McMasterville and on the South Shore: adapting the installation to the building rather than forcing the building to adapt to the equipment.

A Fujitsu AIRSTAGE Altair 500 offers interesting technical features, but the machine alone does not guarantee the result. The support structure, piping, drainage, connections, clearances, and commissioning are all part of the same system.

We use this approach in our heating, air conditioning, and heat pump installations in Montréal, Laval, Longueuil, the North Shore, and the South Shore, whether it is a single-family home, a condo, a multiplex, or a building where the outdoor unit must be installed on a roof.