A flat-roof installation where stability, winter clearance, and the refrigerant route guided every decision
At Saint-Marc-sur-Richelieu, we completed an installation of a Fujitsu AIRSTAGE Altair 500 wall-mounted heat pump whose distinctive feature is immediately apparent: the outdoor unit was not placed at ground level but directly on a flat roof, in an environment where we had to work around the roofing membrane, stone ballast, existing equipment, and a refrigerant route exposed to outdoor conditions.
This type of project requires a different approach from a conventional installation on a wall or ground-level slab. On a roof, we must consider the unit’s weight, the stability of its base, roof protection, vibrations, wind, snow accumulation, winter defrosting, and future accessibility for HVAC maintenance at the same time.
The photo taken after installation shows a Fujitsu AIRSTAGE unit using R-32 refrigerant, mounted on a raised metal support. Beneath the structure, we can see protective surfaces that isolate the mounting from the roof, along with wooden elements used to distribute and stabilize certain support points. The heat pump is therefore kept well above the gravel rather than resting directly on the roof surface.
To the right of the unit, the refrigerant lines and cables follow a protected exterior route before entering the building. The routing is intentionally organized to avoid unnecessarily obstructing the service area around the equipment.
The Fujitsu Altair 500 belongs to the single-zone H series and is available in configurations 09KPAS1, 12KPAS1, 18KPAS1, 24KPAS1, 30KPAS1, and 36KPAS1. The manufacturer specifies, among other features, Inverter technology, the use of R-32, and a heating operating range down to -15 °C.
Why install a heat pump on a roof?
In some properties, a ground-level location simply isn’t the best choice.
This may be caused by:
- the lack of sufficient space along the side;
- an already landscaped yard;
- traffic constraints;
- the proximity of neighbors;
- a façade where we want to avoid a visible compressor;
- a more logical refrigerant line route through the roof;
- the building’s architectural configuration.
On this Saint-Marc-sur-Richelieu project, the roof provided an unobstructed location, but this solution required a much more structured installation.
A compressor should never be placed directly on ballast or a roofing membrane.
The weight of the unit must be properly distributed, and the membrane must be protected against concentrated load points, vibrations, and movement of the support.
A raised base designed to leave space beneath the unit
The structure visible in the photo is one of the most important elements of this installation.
We installed the heat pump on a raised metal support, creating substantial clearance between the bottom of the unit and the roof.
This choice addresses several needs.
First, it keeps the unit above a certain amount of snow accumulation.
Second, it facilitates the drainage of water produced by defrost cycles.
Third, it reduces direct contact between the HVAC equipment and the roof.
Finally, it improves accessibility beneath and around the machine.
In Quebec’s climate, these details become particularly important as soon as the heat pump is used for heating.
Defrosting is even more important on a roof
When a heat pump heats a home in cold weather, the outdoor coil can accumulate frost.
The system must then periodically perform a defrost cycle.
This operation produces water.
For a ground installation, we must prevent this water from gradually forming a mass of ice beneath the compressor. On a roof, we must also ensure that the water can disperse without becoming trapped directly beneath the machine.
The raised support visible here creates a clear space beneath the unit.
Of course, this does not eliminate the need for periodic inspections during the winter, particularly after heavy snowfall or several freeze-thaw cycles.
Protecting the roof before thinking about the heat pump
A common mistake when installing equipment on a roof is to focus solely on the machine.
For us, the roof is an integral part of the project.
The photo clearly shows protective surfaces placed beneath the structure to prevent the metal supports from being applied directly to the roof.
This approach helps distribute the loads more evenly and creates a more suitable interface between the HVAC system and the existing surface.
The goal is simple: install the heat pump without creating a new problem for the building.
Poor installation could cause:
- excessive concentration of loads;
- damage to the membrane;
- vibrations;
- movement of the support;
- difficulties during future roof work.
Anti-vibration isolators beneath the Fujitsu unit
The photo also shows anti-vibration isolators between the compressor feet and the metal support.
On a roof, this detail becomes even more important.
An outdoor unit includes a compressor and a fan. Even when they are quiet, these components generate small mechanical vibrations.
If the unit is rigidly connected to a structure, some vibrations may be transmitted to the building.
The isolators’ role is to limit this transmission.
This is particularly important when the roof is directly above an occupied space.
The unit’s position also makes maintenance easier
We deliberately kept a clear space around the compressor.
The service panel remains accessible, and the front fan faces no immediate obstruction.
That is exactly what we are looking for.
An installation must allow a technician to return several years later to:
- inspect the heat exchanger;
- check the connections;
- take electrical measurements;
- clean the unit;
- diagnose a problem;
- work on the refrigeration circuit when necessary.
A compressor wedged between several rooftop units can turn a simple service call into a complex job.
An outdoor refrigerant line: protection becomes essential
On the right side of the photo, the path of the lines is particularly visible.
The refrigerant lines are grouped and protected along their path across the roof.
On a roof, the lines are exposed to more stresses than inside a building:
- solar radiation;
- rain;
- snow;
- ice;
- significant temperature variations;
- movement during roof maintenance work.
Insulating and mechanically protecting the lines therefore becomes essential.
We also want to avoid having the lines simply laid freely and haphazardly across the surface.
Fujitsu Altair 500: several capacities, but sizing must be determined on a project-by-project basis
The Fujitsu AIRSTAGE Altair 500 range includes several capacities.
According to the manufacturer’s technical specifications, the nominal cooling capacities are 9,000, 12,000, 18,000, 22,000, 30,000, and 33,000 BTU/h for models 09, 12, 18, 24, 30, and 36, respectively.
In heating mode, the stated nominal capacities are 10,000, 14,000, 18,000, 24,000, 30,000, and 34,000 BTU/h.
The exact capacity of the photographed unit is not clear enough in the image to state with certainty. We therefore prefer not to arbitrarily assign a BTU rating to this installation.
For a real-world project, we size the unit according to the building’s characteristics, not according to a simple area-based rule.
The criteria we consider before choosing the capacity
For an installation in Saint-Marc-sur-Richelieu, we can analyze, among other things:
- the area actually served;
- insulation level;
- fenestration;
- sun exposure;
- ceiling height;
- air circulation between rooms;
- the presence of other heating systems;
- the building’s heat loss.
Installing the outdoor unit on the roof does not change the home’s heating requirements, but it can affect certain technical parameters, particularly pipe length and the height difference between the two units.
Pipe lengths suited to complex projects
This is where the Altair 500 becomes particularly appealing for certain projects.
Depending on the model, Fujitsu allows different maximum pipe lengths:
- 66 feet for the 9,000 and 12,000 BTU models;
- 98 feet for the 18,000 and 24,000 BTU models;
- 164 feet for the 30,000 and 36,000 BTU models.
The maximum permitted vertical difference also increases from 49 to 82 and then 98 feet, depending on capacity.
These limits can be critical when a compressor is installed on a roof and the indoor unit is located one or more levels below.
Before carrying out a rooftop heat pump installation, we must therefore check the entire route, not just measure the visible horizontal distance.
Copper pipe sizes vary according to capacity.
Another essential technical detail: not all Altair 500 units use the same pipe sizes.
The Fujitsu specifications indicate:
- 09KPAS1 and 12KPAS1: 1/4 in. liquid and 3/8 in. gas;
- 18KPAS1 and 24KPAS1: 1/4 in. liquid and 1/2 in. gas;
- 30KPAS1 and 36KPAS1: 3/8 in. liquid and 5/8 in. gas.
This information becomes particularly important when we replace an older system.
An existing line that already follows a complex route to the roof may seem worth keeping, but it must be compatible with the new equipment.
We always check the diameter and actual condition of the lines before deciding whether to reuse them.
A new generation using R-32
The marking R32 is clearly visible on the photographed unit.
Fujitsu presents R-32 as a refrigerant with a lower global warming potential than R-410A.
The series documentation indicates a GWP of 675 for R-32, compared with 2,088 for R-410A, representing a stated reduction of 68%.
For installation, this refrigerant change also means that procedures, tools, and practices must be adapted.
R-32 should not be treated as if an older R-410A heat pump were simply being installed.
Inverter technology and power modulation
The Fujitsu Altair 500 uses an inverter compressor.
For the homeowner, this means that the unit can modulate its output.
Instead of operating continuously according to a full-power-then-shutdown logic, it can adjust its output based on demand.
This modulation helps to:
- stabilize the temperature;
- extend certain cycles;
- improve comfort;
- reduce airflow fluctuations;
- adapt consumption to demand.
Fujitsu documentation attributes energy savings of up to 30% to H-Series AIRSTAGE systems, depending on operating conditions.
Real-world performance, noise, winter operation, and maintenance: the details that matter after installation
An HSPF2 rating of up to 26.0
Efficiency varies depending on the selected capacity.
Fujitsu lists the following HSPF2 values:
- 26.0 for the 9,000 BTU model;
- 24.0 for the 12,000 BTU model;
- 22.0 for the 18,000 BTU model;
- 21.5 for the 24,000 BTU model;
- 22.0 for the 30,000 BTU model;
- 21.0 for the 36,000 BTU model.
This is a good example of why we recommend comparing equipment based on its exact combination, not just the range name.
Two Altair 500 units with different capacities do not necessarily have the same efficiency.
Very quiet indoor operation on certain capacities
The technical specifications also indicate indoor sound levels as low as 19 dB(A) in quiet mode on the 9,000 and 12,000 BTU units.
The 18,000 BTU model goes down to 26 dB(A), the 24,000 BTU model to 31 dB(A), and the 30,000 and 36,000 BTU models to 32 dB(A).
This can make a significant difference when an indoor unit is installed in a bedroom or near a living area.
A rooftop location can also reduce some outdoor disturbances
Positioning the compressor on a roof can offer a practical advantage: the unit is away from certain outdoor-use areas.
It is not located immediately next to:
- a terrace;
- a patio door;
- an entrance;
- a side passage;
- a play area.
This does not mean that a rooftop location is always preferable. We assess each building individually.
On some projects, the roof is the logical solution. On others, a wall-mounted support or ground installation will be simpler and more economical.
Wind must be considered on an unobstructed roof
A heat pump installed several meters above the ground is more exposed to wind.
The support must therefore provide good stability.
A configuration in which an obstacle creates significant turbulence in front of or behind the heat exchanger must also be avoided.
In this installation in Saint-Marc-sur-Richelieu, the unit is located in a relatively open area, with sufficient space in front of the large fan.
This arrangement helps maintain adequate airflow.
Heating down to -15 °C: a limitation to understand before purchasing
Fujitsu specifies the Altair 500 range for a heating operating range down to -15 °C.
For Quebec, this information must be presented clearly.
We regularly experience colder periods.
The Altair 500 can therefore provide a significant portion of the annual heating, but it must be selected based on the building’s overall strategy.
If the goal is to obtain a heat pump that can continue operating during temperatures of -25 °C or -30 °C, a range specifically designed for these temperatures may be more appropriate.
We are not trying to suggest that all Fujitsu heat pumps are interchangeable.
Energy Star ratings and financial incentives: always verify the exact model
The Altair 500 series documentation shows several Energy Star ratings, with categories varying by model, including ES, ESCC, and ESME.
This information is useful for homeowners assessing the financial incentives available for a heat pump in Quebec.
However, eligibility for a grant must always be confirmed based on the exact combination of units and the program rules in effect when the project takes place.
The mere fact that a unit belongs to the Altair 500 range is not, by itself, enough to promise a financial incentive amount.
Electrical requirements also vary according to capacity
All models in the series are designed for a 208 to 230 V, 60 Hz, single-phase power supply, but the specified circuit breakers vary according to capacity:
- 15 A for 9,000 BTU;
- 15 A for 12,000 BTU;
- 15 A for 18,000 BTU;
- 20 A for 24,000 BTU;
- 30 A for 30,000 BTU;
- 30 A for 36,000 BTU.
For a unit installed on the roof, we must also plan the electrical route cleanly and safely to the unit.
Mistakes to avoid when installing a rooftop heat pump
An installation like this requires more than simply mounting the unit on the roof.
Among the mistakes we seek to avoid:
- place the unit directly on the membrane or gravel;
- use a support that is too low;
- neglect vibrations;
- leave the lines without adequate protection;
- create an unnecessarily long refrigerant circuit;
- install the compressor too close to a vent or other equipment;
- block access to the service panel;
- ignore snow accumulation;
- fail to account for the vertical difference between the units;
- damage the roof during handling.
This last point is particularly important.
An outdoor unit can weigh several dozen kilograms. Depending on the capacity, the Fujitsu specifications indicate outdoor unit weights ranging from approximately 51 lb to 117 lb.
Rooftop handling must therefore be organized methodically.
Annual maintenance deserves particular attention on a roof
A rooftop heat pump should not be forgotten after installation.
We recommend checking the following periodically:
- the condition of the support;
- the vibration isolators;
- the outdoor heat exchanger;
- the clearance around the unit;
- the condition of the line insulation;
- the accumulation of leaves;
- the presence of snow or ice;
- the general condition of the area beneath the unit.
The roof visible in this installation is surrounded by many mature trees.
This creates a pleasant environment, but it also means that leaves and other debris can reach the roof.
Keeping the heat exchanger clean directly contributes to the system’s performance.
This project illustrates a less visible part of our work at AirGreen
When a customer sees a wall-mounted heat pump, they often think mainly of the indoor unit.
For us, exterior design is just as important.
For this Saint-Marc-sur-Richelieu project, we had to think about the roof before even considering the connections.
We had to organize:
- the unit’s position;
- its height;
- its support;
- roof protection;
- vibrations;
- the lines;
- service access;
- winter conditions.
It is precisely this type of detail that distinguishes a quick installation from a HVAC installation designed to last.
An approach we apply throughout Greater Montreal
Our projects in Montreal, Laval, Longueuil, on the North Shore, and on the South Shore never look exactly the same.
In Montreal, we frequently encounter flat roofs on plexes and denser buildings.
In Laval and on the North Shore, ground installations are more common, but certain homes or properties also require a rooftop solution.
In Longueuil, on the South Shore, and in municipalities such as Saint-Marc-sur-Richelieu, we often have to adapt the installation method to buildings that differ greatly from one another.
Our role therefore involves more than simply selling a Fujitsu Altair 500.
We must determine where it will operate most effectively, how to protect the building, and how to make maintenance easier in the years ahead.
A Fujitsu heat pump properly integrated into the building, even on the roof
This Fujitsu AIRSTAGE Altair 500 installation in Saint-Marc-sur-Richelieu showcases a more technical aspect of wall-mounted heat pump installation.
The compressor is placed on a raised metal support equipped with vibration isolators and installed in a protected area of the roof. The lines follow an organized outdoor route, while the front of the fan and the service panels remain unobstructed.
The unit benefits from the features of the Altair 500 series: Inverter technology, R-32 refrigerant, different capacities, several Energy Star efficiency levels depending on the model, quiet operation, and additional control options. Fujitsu documentation also mentions ProCore indoor coils, Hydro Fin fins, and several optional interfaces, including Wi-Fi, BACnet, Modbus, and a 24 V thermostat, depending on the selected configuration.
But in this project, our work did not stop at the machine’s specifications.
We had to create an installation that could truly coexist with the building, its roof, and our climate.
At AirGreen, it is this attention to elements that do not always appear in the brochure — support, clearance, piping, vibrations, access, drainage, and roof protection — that transforms a high-performance heat pump into a complete HVAC installation.