An HVAC installation on a flat roof where positioning matters just as much as the heat pump’s performance
This wall-mounted heat pump installation in Sainte-Marthe-sur-le-Lac illustrates a reality that is often underestimated: on a roof already occupied by several air-conditioning units, ventilation ducts, mechanical outlets, and electrical equipment, the quality of the work depends not only on the equipment selected. It also depends on its location, stability, clearance, routing of the lines, and future accessibility for maintenance.
For this project, we installed a Hitachi airHome 600 heat pump on a flat gravel-covered roof. The outdoor unit is located in a mechanical area that already contains several condensers, large ventilation units, and various roof penetrations. This concentration of equipment required precise planning to prevent hot-air recirculation, vibrations transmitted to the building, and complicated service work during future HVAC maintenance.
The result is a clean, well-structured installation where the Hitachi unit remains accessible without blocking the other equipment on the roof.
Why choose the Hitachi airHome 600?
The Hitachi airHome 600 is an Inverter technology wall-mounted heat pump designed to provide three main functions:
- cooling;
- heating;
- improved indoor air quality.
The range includes systems from 9,000 to 24,000 BTU/h, depending on the selected combination. It offers efficiency ratings of up to TRÉS2 of 23.0 and a region 5 CPSC2 of 9.2. It is designed to continue heating down to an outdoor temperature of -25 °C and can deliver up to 100% of its heating capacity at -15 °C, depending on the selected model. All combinations presented by the manufacturer are ENERGY STAR certified.
These characteristics are particularly relevant in the Montreal area, where a system must cope with:
- periods of humid heat;
- rapid temperature fluctuations;
- cold nights;
- prolonged winter conditions;
- greater wind exposure on a roof.
Inverter technology modulates the compressor speed rather than operating only in full on-and-off cycles. This allows the heat pump to adjust its output to the room’s actual needs, promoting a more stable temperature and generally quieter operation.
Capacity determined according to the building, not solely its area
The capacity of a wall-mounted heat pump should never be selected simply based on a square-footage figure. A properly sized installation must take several factors into account:
- the building’s orientation;
- the size and type of windows;
- the level of insulation;
- ceiling height;
- the floor being served;
- sun exposure;
- heat loss;
- the number of occupants;
- the layout of the rooms;
- the presence of other heat sources.
An oversized heat pump can reach the desired temperature too quickly and reduce its continuous operating time. In summer, this can impair dehumidification. An undersized unit, on the other hand, may run almost continuously during the hottest days or periods of intense cold.
At AirGreen, we therefore validate capacity based on the actual characteristics of the space to be heated and cooled. The airHome 600 series offers several capacity options, with nominal cooling capacities of 9,000, 12,000, 15,000, 18,000 and 22,000 BTU/h, the latter marketed in the 24,000 BTU category.
The main challenge: integrating the unit into an already crowded mechanical area
The project photograph clearly shows that the Hitachi unit was not installed on an empty roof. Several outdoor units are located in the immediate vicinity, including wall-mounted condensers and larger ventilation equipment.
In such an environment, we must avoid placing the heat pump in an area where it could draw in hot air discharged by another unit. Air recirculation can cause:
- increased operating pressure;
- reduced cooling efficiency;
- prolonged compressor operation;
- premature wear;
- protective shutdowns during periods of extreme heat.
We left a clear space in front of the fan of the Hitachi unit to facilitate air discharge. The sides required for airflow and technical servicing also remain accessible.
Do not confuse available space with a suitable location
On a roof, an open space is not automatically a suitable location. You need to check:
- the direction of the air discharge;
- the proximity of other condensers;
- areas where snow accumulates;
- defrost water drainage;
- the base's ability to support the unit;
- the distance from ventilation ducts and outlets;
- the route of the refrigerant lines;
- safe access for technicians.
This analysis is important in Sainte-Marthe-sur-le-Lac, but it applies equally to rooftop installations in Montréal, Laval, Longueuil, on the North Shore, and on the South Shore.
A raised base to protect the roof and stabilize the unit
The outdoor unit shown in the photo is installed on wooden supports resting on the roof surface. Insulating elements are placed beneath the support points to reduce direct contact and improve stability.
This method offers several advantages when properly executed:
- it distributes the weight of the unit;
- it prevents the metal feet from resting directly on the roof;
- it limits movement of the unit;
- it reduces vibration transmission;
- it creates separation between the unit and the gravel;
- it facilitates water drainage around the base.
On a flat roof, protecting the membrane is a priority. An improperly positioned support, a sharp metal component, or repeated movement caused by vibrations can eventually damage the waterproofing surface.
Managing vibrations on a roof
Even a modern, quiet heat pump produces some mechanical vibration. On a roof structure, these vibrations can be transmitted to the joists, walls, and ceilings.
A professional installation may require, depending on the building:
- anti-vibration pads;
- a complete rubber base;
- support rails;
- spring supports for heavier equipment;
- a structure designed to distribute the load.
The solution must be selected according to the weight of the unit, the roof construction, and the acoustic sensitivity of the spaces below.
Protected and accessible connections
The refrigerant lines and wiring are bundled and insulated before entering the outdoor unit. Protecting the lines is particularly important on a roof because they are exposed to:
- solar radiation;
- rain;
- freezing;
- wind;
- temperature variations;
- to the work of other trades.
Damaged insulation can lead to condensation, loss of efficiency, and accelerated deterioration of the piping. We therefore pay attention to the continuity of the insulation, the fastening of the lines, and the bend radii.
Depending on the airHome 600’s capacity, the refrigerant connections vary. The liquid line is 1/4 in throughout the range, while the gas line may be 3/8 in, 1/2 in, or 5/8 in. Using the wrong diameter can affect oil return, operating pressures, and the system’s actual capacity.
A power supply suited to the installed combination
Electrical requirements also vary depending on the selected capacity. The range operates at 208-230 V, single-phase, 60 Hz.
The published specifications indicate, among other things:
- 9,000 BTU: MCA of 12 A and maximum protection of 15 A;
- 12,000 BTU: MCA of 14 A and maximum protection of 15 A;
- 15,000 BTU: MCA of 16 A and maximum protection of 25 A;
- 18,000 BTU: MCA of 20 A and maximum protection of 25 A;
- 22,000 BTU: MCA of 20 A and maximum protection of 25 A.
The circuit breaker must not be selected based on a general estimate. It must correspond to the requirements on the nameplate, the installation manual, and the applicable electrical circuit regulations.
In the photo, the electrical connection is installed on the service side of the unit, allowing reasonable access for inspections and future work.
Comfort, air quality, and maintenance: what this installation brings to everyday life
Heating suited to Quebec’s climate
The Hitachi airHome 600 is designed to maintain heating down to -25 °C. Available capacity gradually decreases as the outdoor temperature drops, as with any air-source heat pump, but the system remains operational in demanding winter conditions.
Depending on the selected capacity, the maximum heating output at -25 °C ranges from approximately 7,200 to 15,000 BTU/h. This figure is more useful than the nominal capacity alone because it indicates what the heat pump can actually deliver during cold periods.
For some buildings, an additional heating source is still recommended. The role of this source depends on the load calculation, air distribution, and desired comfort level.
Quiet operation indoors
Depending on the model and fan speed, the indoor units in the range can operate at approximately 29 dB(A) in their quietest setting. This level is well suited to bedrooms, offices, and living spaces when the indoor unit’s location is carefully planned.
However, acoustic comfort also depends on the installation. An improperly secured indoor unit, a line in contact with the structure, or a noisy condensate pump can offset some of the system’s acoustic benefits.
FrostWash 3.0: an indoor coil that is easier to maintain
The FrostWash 3.0 technology uses a three-step cycle:
- the coil is heated to soften greasy contaminants;
- it is cooled until frost forms, trapping the particles;
- the ice melts and carries away some of the accumulated dirt.
The range also includes a stainless-steel prefilter and a PM2.5 activated carbon filter. These devices help reduce particles and certain odors when the heat pump is operating.
However, this function does not replace professional wall-mounted heat pump cleaning. The fan wheel, condensate pan, drain, filters, and internal surfaces must still be inspected periodically.
Mold protection
After certain cycles, the mold protection function circulates air through the internal components and heats the coil to reduce residual moisture. This function helps limit conditions conducive to odors and mold, but it cannot eliminate contamination that is already established.
To achieve good results, we recommend:
- clean the filters regularly;
- keep the drain clear;
- avoid cutting off the power immediately after each use;
- have the unit inspected if a persistent odor appears;
- schedule thorough maintenance based on usage and environment.
Wi-Fi control with airCloud Go
The Wi-Fi adapter is included with the models presented in the series documentation. The airCloud Go app notably allows you to:
- to adjust the temperature remotely;
- to schedule weekly schedules;
- to monitor estimated energy consumption;
- to use certain voice commands;
- to automate operation based on occupancy or location.
These functions are useful for a residence with variable occupancy, a rental property, or a space with regularly changing schedules.
Smart Eco and SleepSense
The Smart Eco motion sensor can detect when a room is unoccupied and gradually reduce energy consumption. When someone returns, the heat pump resumes its initial operation.
The SleepSense function adjusts the temperature during the night to limit uncomfortable fluctuations and unnecessary energy consumption. However, the effectiveness of these functions depends on the positioning of the indoor unit and the sensor’s ability to properly see the occupied area.
Mistakes to avoid when installing on a roof
Installing the unit too close to another condenser
Two units placed facing each other or too close together can exchange their exhaust air. The problem becomes more significant during a heat wave, when all systems are operating simultaneously.
Place the unit directly on the membrane
Vibrations, weight, and wind-induced movement can damage the roof. An appropriate base is necessary.
Neglecting defrost water
In winter, a heat pump produces water during defrost cycles. This water must be able to drain away without forming an accumulation of ice beneath the unit or in a traffic area.
The Hitachi airHome 600 includes a heating element in the outdoor condensate pan, which helps manage cold conditions. Drainage around the unit nevertheless remains essential.
Making the service panel inaccessible
The space in front of the electrical panel and connections must remain clear. An installation that is too tight increases service time and may prevent certain repairs.
Choosing the capacity solely based on the previous unit
An old air conditioner may have been oversized or poorly suited. Replacement should be based on the building’s current needs, not automatically on the capacity of the removed equipment.
Eligibility for financial incentives
The manufacturer presents the airHome 600 series as ENERGY STAR certified and eligible for most provincial heat pump incentives. Actual eligibility, however, depends on the exact combination of indoor and outdoor units, the recognized heating capacity, the type of building, and the program criteria in effect when the application is submitted.
Before quoting a price, we verify in particular:
- the complete model numbers;
- the certification reference;
- the heating capacity at the required temperature;
- the installation address;
- the type of residence;
- the purchase and installation date;
- the requested documents and photographs.
Why entrust this type of project to AirGreen?
A rooftop HVAC installation requires more than a refrigerant connection. It requires an understanding of airflow, structural considerations, vibrations, water drainage, and coordination with other mechanical equipment.
At AirGreen, we install wall-mounted heat pumps in Montreal, Laval, Longueuil, on the North Shore, and on the South Shore, including projects where the outdoor unit must be installed on a roof, terrace, balcony, or elevated structure.
For this project in Sainte-Marthe-sur-le-Lac, our work allowed us to integrate a Hitachi airHome 600 into an already occupied mechanical area while maintaining the required clearances, a stable base, and convenient access to service components.
Choosing the right heat pump is important. However, the way it is installed determines much of its efficiency, noise level, and lifespan.