A rooftop installation designed to protect the building and maintain technical access
On this project in Laval-Ouest, the outdoor unit of the Hitachi airHome 800 wall-mounted heat pump had to be integrated into a flat roof already occupied by several mechanical components. The site photograph shows a typical environment in some Laval buildings: a membrane protected by gravel, sheet-metal ventilation ducts, existing wiring, and limited circulation space around the equipment.
The challenge was therefore not simply to place a condenser on the roof. We had to create a stable base, protect the roofing, limit vibration transmission, and maintain sufficient clearances both for operation and for future HVAC maintenance.
We installed the Hitachi unit on two treated wooden crossbeams, which were themselves supported by protective pads separating the structure from the roof surface. Anti-vibration isolators were placed under the unit’s feet to reduce vibrations transmitted to the support.
This method made it possible to achieve an installation that was:
- stable despite starting and defrost cycles;
- raised above the gravel;
- accessible for inspections;
- protected from direct contact with the roofing;
- better suited to water, snow, and debris;
- integrated without obstructing nearby ventilation equipment.
Why install a wall-mounted heat pump on a flat roof?
In several areas of Laval, particularly in buildings where the yard is narrow or already developed, a ground-level installation is not always desirable. The condenser could obstruct a passage, be exposed to impacts, reduce the available space, or end up directly in snow accumulation.
A rooftop installation can therefore be advantageous, provided it is carefully planned. It can, among other things:
- clear exterior walls and circulation areas;
- reduce the unit’s visual impact from the street;
- move the unit away from high-traffic areas;
- limit the risk of damage caused by a lawn mower, shovel, or vehicle;
- bring the unit closer to a piping route suited to the indoor configuration.
The roof is not a universal location, however. Before recommending this solution, we must check the structure, roofing, refrigerant line route, height difference between the units, roof access, prevailing winds, and how defrost water can be drained.
A base that does not compromise the roof's watertightness
One of the most costly mistakes when carrying out an HVAC installation on a flat roof is securing a unit without considering the waterproofing system. An improperly prepared penetration can eventually cause a leak, with damage that far exceeds the cost of the heat pump.
On this Laval-Ouest job site, the outdoor unit rests on a base that distributes its weight without improvised fasteners penetrating the roof. The crossbars keep the unit above the gravel and create an even footing despite the uneven texture of the surface.
The black elements placed beneath the wood also serve to separate the base from the roof. This detail reduces direct friction, helps distribute the load, and prevents the wood from simply sinking into the gravel over time.
Leveling remains essential
An outdoor unit must be installed stably and properly leveled. A tilted unit can cause several problems:
- improper drainage of the water produced during defrosting;
- increased vibrations;
- uneven stress on the condenser feet;
- water accumulating in part of the lower pan;
- abnormal mechanical noise;
- gradual movement of the support.
On a gravel-covered roof, the level cannot be assessed by eye alone. We must prepare the area, position the supports, check stability, and ensure that the base does not tip when the fan is operating.
Visible anti-vibration isolators beneath the unit
The photo shows anti-vibration elements beneath the condenser feet. This detail is particularly important on a roof, since vibrations can be transmitted to the building structure and become noticeable in the rooms below.
Even a quiet heat pump can generate an unpleasant humming sound when installed directly on a rigid surface. The problem is not necessarily caused by the machine, but by resonance between the unit, its support, and the building.
To limit this transmission, we take into account:
- the weight of the installed model;
- the rigidity of the crossbars;
- the distance between support points;
- the type of isolator used;
- the frequency of the vibrations;
- the presence of rooms or quiet spaces beneath the roof.
Proper isolation does not mean that the unit should be placed on a soft or unstable base. The support must remain firm while reducing the transmission of mechanical vibrations.
Integration into an already crowded mechanical environment
To the left of the heat pump, the photograph shows metal ducts and another piece of outdoor equipment. Installing a unit in this type of environment requires precise coordination so that the new condenser blocks neither maintenance nor ventilation for the existing systems.
We must maintain sufficient space for:
- air discharge from the fan;
- air intake through the coil;
- removal of the service panels;
- access to the refrigerant valves;
- electrical measurements;
- condenser cleaning;
- work on nearby ducts;
- the safe movement of technicians.
A unit installed too close to a duct may draw in its own discharged air. In summer, this increases the temperature of the air entering the condenser and reduces its efficiency. In heating mode, poor airflow can also hinder defrosting and promote frost buildup.
The front of the Hitachi unit visible in the photo remains largely unobstructed. This choice allows the fan to discharge air freely above the roof.
How the heat pump behaves under snow
Installing a heat pump on a roof does not mean that it is automatically protected from snow. Depending on the wind, significant accumulations can form around mechanical equipment, behind ducts, or near parapets.
Raising the unit helps keep the underside of the condenser clear. It also facilitates the drainage of water produced during defrost cycles.
In winter, we recommend that the owner or building manager monitor:
- the formation of a snowdrift against the coil;
- the blockage of the front of the fan;
- ice under the unit;
- snow accumulation between the crossbars;
- ice coming from nearby equipment;
- objects blown by the wind around the condenser.
Snow must never be pushed directly against the unit. You should also avoid breaking the ice with a metal shovel, a hammer, or any object that could damage the coil.
Paying particular attention to defrost water
In heating mode, the heat pump cools its outdoor coil to capture the energy present in the air. When moisture freezes on the coil, the unit starts a defrost cycle. A sometimes considerable amount of water is then released.
On a flat roof, this water must be able to reach the drainage system without creating a sheet of ice in a service passage. The unit’s location, the roof slope, and the position of the roof drains must therefore be considered before installation.
In particular, we avoid placing the condenser:
- in a depression where water accumulates;
- directly in front of a drain that must remain accessible;
- near a place where ice could block a door;
- under a water discharge from another piece of equipment;
- against a parapet that promotes heavy snow accumulation.
The Hitachi airHome 800: efficiency, cold-weather heating, and easier maintenance
The Hitachi airHome 800 is an Inverter compressor wall-mounted heat pump available in several capacities. Depending on the selected pairing, the range includes models with nominal cooling capacities of 9,500, 12,500, 18,000, and 22,000 BTU/h, with nominal heating capacities ranging from 12,000 to 25,400 BTU/h.
The precise capacity installed for this project cannot be confirmed from the photograph alone, since the rating plate is not legible. At AirGreen, we avoid inferring a unit's capacity from its exterior appearance. The model must be verified on the rating plate and selected according to the building's actual heating requirements.
Performance of up to 26.5 TRÈS2
The airHome 800 range offers a TRÈS2 of up to 26.5 and a CPSC2 for climate region 5 of up to 9.7, depending on the selected capacity. The models use R32 refrigerant and are designed to provide heating down to an outdoor temperature of −30 °C.
The technical data sheet presented on page 4 of the brochure also indicates the capacities available at different outdoor temperatures, sound levels, electrical requirements, dimensions, and piping diameters specific to each pairing. These differences confirm why the choice of model and piping must never be improvised.
Low-temperature heating capacity
According to the manufacturer's data, all four models retain significant maximum capacity at −20 °C:
- 9,000 model: up to 12,000 BTU/h;
- 12,000 model: up to 13,500 BTU/h;
- 18,000 model: up to 21,600 BTU/h;
- 24,000 model: up to 25,500 BTU/h.
At −30 °C, residual capacity remains available, varying by model. This information is important for homeowners who wish to use their wall-mounted heat pump as their primary heating source for much of the winter.
However, this does not mean that a wall-mounted unit automatically works as the sole system for every building. Heat losses must be calculated, and supplemental heating may still be necessary during cold snaps or in rooms far from the indoor unit.
Inverter technology and more stable comfort
The Inverter compressor adjusts its speed according to demand. Instead of operating only at full capacity and then stopping, it can modulate its output to maintain a more consistent temperature.
This modulation contributes to:
- reduce temperature fluctuations;
- limit certain on-off cycles;
- improve comfort during the shoulder seasons;
- adapt consumption to the building's needs;
- promote quieter operation;
- better manage Laval's rapid climate variations.
However, an Inverter system must be sized correctly. An oversized unit can quickly reach the requested temperature without providing optimal dehumidification in summer. Conversely, an undersized system may run continuously without fully meeting the heating load.
FrostWash 3.0 and Mold Guard 2.0
The Hitachi airHome 800 includes several functions related to keeping the indoor unit clean.
FrostWash 3.0 uses a cooling and thawing cycle to trap and then remove some of the contaminants present on the heat exchanger. The coil is first heated, then cooled to form ice, and finally rinsed as the ice melts.
The Mold Guard 2.0 function monitors internal conditions when the unit is turned off. If humidity and temperature become favorable for mold growth, the system can heat the coil to dry it.
These technologies help maintain cleanliness, but they do not replace thorough cleaning. The filters, fan, condensate pan, and drain must still be inspected.
PM2.5 filtration and stainless steel pre-filter
The indoor unit includes a PM2.5 activated carbon filter as well as a stainless steel pre-filter. This combination helps trap certain particles and reduce certain odors.
To maintain adequate airflow, the filters must be cleaned regularly. A clogged filter can reduce airflow, increase noise, and decrease heating or cooling capacity.
Maintenance frequency varies depending on:
- presence of pets;
- amount of dust;
- use of the heat pump;
- proximity to a road;
- renovation work;
- pollen and surrounding vegetation.
airCloud Go and remote control
The Wi-Fi interface that enables use of the airCloud Go app is designed to be concealed inside the indoor unit. This allows the owner to adjust the temperature, schedule operating times, and view certain operating data remotely.
The available features include:
- the weekly timer;
- temperature control;
- the display of certain error codes;
- consumption estimates;
- compatible voice control;
- Smart-Fence;
- the activation of cleaning functions.
For a building in Laval-Ouest with a variable schedule, remote control makes it possible to avoid unnecessarily maintaining a high or low temperature during absences.
Different electrical requirements depending on capacity
The airHome 800 models operate at a nominal voltage of 208 or 230 volts, depending on the unit. Circuit requirements vary with capacity:
- the 9,000 and 12,000 BTU models have a minimum circuit ampacity of 14 A and maximum protection of 25 A;
- the 18,000 and 24,000 BTU models have a minimum circuit ampacity of 20 A and maximum protection of 35 A.
These values are used to plan the circuit, but the electrical installation must always be carried out according to the unit's nameplate and the applicable building requirements.
The wire gauge and circuit breaker must not be selected solely based on the nominal power advertised.
The piping must match the exact model
Refrigerant connections vary according to capacity:
- 9,000 and 12,000 BTU: 1/4 in. liquid and 3/8 in. gas;
- 18,000 BTU: 1/4 in. liquid and 1/2 in. gas;
- 24,000 BTU: 3/8 in. liquid and 5/8 in. gas.
This variation is particularly important when replacing an old heat pump. Existing piping cannot be reused simply because it already reaches the right location.
We check:
- the diameters;
- the condition of the insulation;
- the total length;
- the height difference;
- internal cleanliness;
- compatibility with the refrigerant;
- the accessibility of the connections.
For a rooftop installation, respecting the maximum piping height is also essential. The product line allows a maximum vertical difference ranging from 65.6 to 98 feet, depending on the model.
Mistakes to avoid when installing on a roof
The most common problems do not always come from the heat pump itself. They are often related to the installation.
We recommend avoiding:
- a unit placed directly on gravel;
- crossbars left unprotected against moisture;
- an unstable base;
- an appliance installed too close to a duct;
- an air outlet directed toward an obstacle;
- unprotected lines;
- an inaccessible roof drain;
- a lack of vibration isolators;
- an unmeasured refrigerant line run;
- start-up without a leak test or vacuuming.
The vacuum process removes air and moisture from the refrigeration circuit. It must be performed with appropriate instruments before releasing the refrigerant charge.
Recommended Maintenance for This Laval-Ouest Installation
Since the outdoor unit is located on a roof, maintenance must be integrated into the building's normal management. Access should not be improvised only when a breakdown occurs.
We recommend:
- a visual inspection before winter;
- removing leaves and debris around the condenser;
- checking the stability of the crossbars;
- inspection of the vibration isolators;
- checking the pipe insulation;
- cleaning the coil when necessary;
- checking the roof drains;
- inspection of the indoor unit and condensate drain;
- periodic filter cleaning.
After roofing work, it is also necessary to check that the roofers have not moved the unit, blocked its clearance, or covered the base with materials.
Eligibility for Rebates and Warranty Registration
Hitachi documentation presents the airHome 800 as equipment eligible for several provincial incentives. Final eligibility, however, depends on the exact match, its reference number, the program in effect, and the building's characteristics.
Before calculating financial assistance, we must confirm:
- the indoor model;
- the outdoor model;
- the recognized capacity;
- the applicable certification;
- the installation address;
- the type of building;
- the replaced system;
- the purchase and installation date.
The warranty must also be registered according to the manufacturer's terms. The brochure indicates a standard warranty as well as extended protections that may require online registration or the purchase of an upgrade.
The result: a clean, stable installation adapted to the roof
This Hitachi airHome 800 wall-mounted heat pump installation in Laval-Ouest illustrates the importance of details that are often invisible from inside the building. The unit is elevated, supported on a base that distributes its load, and equipped with isolators to reduce vibrations.
Its front remains unobstructed, neighboring equipment remains accessible, and the roof is not used as a simple surface on which to place the condenser.
At AirGreen, we apply this same rigor to our wall-mounted heat pump installations, central systems, and HVAC solutions in Laval, Montréal, Longueuil, the North Shore, and the South Shore. Choosing the equipment matters, but implementation, connections, drainage, support, and commissioning determine the project's true quality.