A rooftop installation designed to free up ground space and serve two distinct zones
At Saint-Constant, this HITACHI airHome Multi multi-zone heat pump installation had a specific objective: to provide independent comfort control in two parts of the building without obstructing the yard, side walkways, or outdoor living spaces. The selected solution was to install the outdoor unit on the flat roof, on an elevated structure adapted to the requirements of a climate like that of the South Shore of Montreal.
At first glance, a rooftop installation may seem simpler than a ground-level installation. The unit is away from traffic areas and remains discreet from the street. In reality, this type of project requires careful preparation. Membrane protection, support stability, future access for maintenance, refrigerant line routing, and vibration management must all be assessed before the equipment is permanently secured.
In the project photo, the HITACHI outdoor unit sits on an elevated metal support. The support is installed above long pieces of wood placed on protective strips to distribute the weight more effectively and prevent a rigid contact point from directly damaging the roof. This configuration also keeps the bottom of the heat pump clear, making it easier for water produced during defrost cycles to drain.
The result is a clean, accessible, and well-organized HVAC installation, designed for both immediate operation and long-term system durability.
Why a dual-zone heat pump was the right choice for this Saint-Constant building
A dual-zone multi-zone heat pump connects two indoor units to a single outdoor unit. Each indoor unit serves a particular room or area of the building. This makes it possible to adjust the temperature, fan speed, and operating schedules independently in both zones.
This independence is particularly useful when heating and cooling needs are not the same everywhere. A south-facing room can warm up quickly during the afternoon, while a bedroom on the other side of the building remains cooler. With a central system controlled by a single thermostat, it is often difficult to correct this difference without overcooling part of the property.
The HITACHI airHome Multi system allows you to:
- to use a single outdoor unit for multiple indoor units;
- to maintain different setpoints from one zone to another;
- to turn off one indoor unit while the other continues operating;
- to adjust fan speeds separately;
- to cool, dehumidify, or ventilate zones during the summer;
- to heat rooms individually during the winter.
However, it is important to understand a key feature of multi-zone systems: indoor units connected to the same heat pump operate in a shared primary mode. In summer, they can be set to cooling, dehumidification, or fan mode. In winter, they operate in heating or fan mode. It is therefore not possible to heat one room while another is actively being cooled by the same outdoor unit.
This clarification is part of the information we provide before every multi-zone heat pump installation in Saint-Constant, Montreal, Laval, Longueuil, on the North Shore, and on the South Shore. A well-chosen system must correspond not only to the building’s area, but also to its occupants’ actual habits.
A multi-zone platform that can evolve according to the number of rooms
The HITACHI airHome Multi lineup includes outdoor units ranging from 18,000 to 42,000 BTU/h that can power two to five indoor units, depending on the model. The lineup’s dual-zone configuration is represented by the RAM-G18N2HAA outdoor unit, designed for two indoor connections and offering a nominal cooling capacity of 18,000 BTU/h and a nominal heating capacity of 22,000 BTU/h.
However, the final choice of indoor capacities should never be based solely on the number of rooms. A closed bedroom, an open living room, an attic-level floor, or a room with extensive glazing do not have the same heating and cooling loads.
At AirGreen, we take the following factors into account:
- the area and volume of each zone;
- window orientation;
- insulation level;
- air infiltration;
- ceiling height;
- solar exposure;
- the number of occupants;
- heat-generating appliances;
- of the outdoor unit’s actual capacity when both zones operate simultaneously.
A common mistake is to simply add up the nominal capacities listed on the indoor units and assume that the outdoor unit will deliver this maximum output to all zones at the same time. In a multi-zone system, the available capacity is distributed according to demand. Sizing must therefore be carried out as a cohesive system.
The main challenge: securely installing the equipment without compromising the roof
The white membrane visible on this flat roof forms an essential part of the building envelope. It must not be punctured or crushed unnecessarily. Before positioning the heat pump, we must determine how to transfer its load to the roof while limiting concentrated stresses.
In this installation, the metal support is placed on wooden sleepers that are long enough to distribute the weight over a larger surface area. Protective strips separate the wood from the membrane. This method helps prevent:
- abrasion caused by movement and vibrations;
- excessive pressure on a small area;
- direct contact between metal parts and the membrane;
- the permanent accumulation of moisture beneath certain support points;
- the instability of the unit during strong winds.
The support also keeps the outdoor unit at a useful height above the roof. In heating mode, a heat pump extracts heat from the outdoor air. Frost may form on its coil and then melt during defrosting. The water must be able to leave the unit without becoming trapped immediately beneath its base.
On a South Shore roof, this issue becomes even more important in winter. Defrost water can refreeze around an inadequately elevated unit. Ice buildup can hinder drainage, block certain openings, or complicate access to the system.
Clearances around the unit and air circulation
An outdoor unit must not simply “fit” into the available space. It needs to breathe. The fan must be able to expel air without that air being immediately drawn back toward the coil. Significant recirculation reduces performance and can increase electricity consumption.
The photo shows that the front of the fan remains unobstructed. Permanent obstacles are far enough away not to directly block the air discharge. We also took into account the existing rooftop equipment, including vents, mechanical outlets, and the other outdoor unit located behind the main heat pump.
When there are several units on a roof, we avoid positioning them so that the hot or cold air discharged by one machine is drawn in by the next. This planning is especially important for multi-zone heat pump projects in Montreal and Greater Montreal, where roofs are often occupied by ducts, plumbing vents, chimneys, skylights, and various mechanical equipment.
Refrigerant lines protected along their entire length
The refrigerant lines visible at the base of the unit are bundled together and covered with black insulation. This insulation must be continuous and able to withstand outdoor conditions. It protects the lines against heat loss and limits condensation.
On a roof, it must also withstand:
- to ultraviolet radiation;
- to rain and snow;
- to temperature variations;
- to movement caused by expansion;
- to future work carried out near the equipment.
The bends must be sufficiently wide to avoid crushing the copper pipes. A bend that is too tight can restrict refrigerant flow or weaken the copper. We also plan a routing path that does not place excessive strain on the unit connections.
The airHome Multi range uses R32 refrigerant. According to the manufacturer's documentation, compatible indoor units include a sensor designed to detect a potential leak, with a visual and audible alarm depending on the type of unit and the accessories used.
Particular attention to electrical connections
The electrical cable visible at the back of the unit must be installed to withstand weather conditions and movement. It must not be allowed to rest in an area where water can accumulate or place tension on the junction box.
Electrical requirements depend on the outdoor model selected. For reference, the dual-zone RAM-G18N2HAA model operates on a 208–230 V, single-phase, 60 Hz power supply. The documentation indicates a minimum circuit ampacity of 16 A and maximum overcurrent protection of 25 A. These values apply to the model shown in the brochure; the nameplate on the installed unit and the electrical requirements applicable to the job site must always be verified before connection.
This distinction is essential. A circuit breaker should not be selected simply based on an estimate of BTU capacity. Technicians must consult the manufacturer's MCA and MOP values, check the existing wiring, and coordinate the required electrical work.
The concrete benefits of the HITACHI airHome Multi for year-round comfort
The HITACHI airHome Multi was designed to provide cooling and heating on a single platform. Depending on the configuration selected, the range reaches a SEER2 of up to 23.0 and an HSPF2-5 of up to 7.85. The manufacturer also indicates heating operation down to an outdoor temperature of -20 °C.
For Saint-Constant homeowners, this operating range means the heat pump can contribute to heating during a significant part of the winter. However, the actual available capacity decreases as the outdoor temperature drops. For example, the dual-zone model documentation indicates a maximum heating capacity of 14,300 BTU/h at -15 °C and 9,700 BTU/h at -20 °C.
These data illustrate why we never present a heat pump as merely a single nominal figure. An 18,000 BTU/h unit in cooling mode does not necessarily provide 18,000 BTU/h of heating on the coldest days. Choosing a system requires considering low-temperature performance, the building’s load, and the possible presence of supplemental heating.
More precise comfort in each zone
The main benefit occupants experience is the ability to avoid treating the entire building in the same way. A little-used zone can be set to a more moderate temperature, while the occupied space remains comfortable.
This flexibility avoids several common problems:
- a bedroom that is too cold because the main thermostat is located in the living room;
- a floor that is too hot during the summer;
- a rarely occupied room being unnecessarily air-conditioned;
- significant differences between north- and south-facing façades;
- the constant use of portable heaters or window air conditioners.
Inverter modulation adjusts output according to demand instead of operating only at full capacity. As the temperature approaches the setpoint, the system can slow down and maintain more consistent comfort.
Several indoor unit styles to suit the building
The airHome Multi outdoor unit can be combined with different types of indoor units. The HITACHI brochure specifically lists:
- airHome 400 wall-mounted units;
- airHome 650 wall-mounted units;
- airHome Floor floor consoles;
- ceiling mini-cassettes;
- concealed ducted units.
This variety makes it possible to design an installation suited to the building’s architecture. A wall-mounted unit is often suitable for bedrooms and open spaces. A floor console may be preferred when wall clearance is limited. A mini-cassette distributes air in four directions. A ducted unit provides a more discreet appearance when the necessary technical space is available.
In a dual-zone project, it is therefore possible to combine two different solutions according to the needs of each room, subject to compatibility with the outdoor unit and validation against the manufacturer’s combination tables.
Filtration, coil cleaning, and humidity control
Depending on the indoor units selected, the system can incorporate several air-quality features. HITACHI notably offers FrostWash technology, which uses a freeze-and-thaw cycle to clean the indoor heat exchanger coil. The Mold Guard function runs the fan after cooling or dehumidification operations to help dry the internal components and limit moisture-related odors.
Filtration options vary according to the type of indoor unit. Some units use a PM2.5 activated carbon filter, while the mini-cassettes are paired with the ViroSense S filter.
These features do not replace HVAC maintenance. Filters must still be inspected and cleaned periodically. The drain pan, coil, blower wheel, and condensate line must also remain clean. A self-cleaning function can slow the buildup of dirt, but it does not eliminate the need for professional maintenance.
Smart control and remote scheduling
An optional airCloud Go interface may enable remote control of the system. Users can schedule operating periods, adjust settings, and view certain information from a compatible device.
Some indoor units may also offer a motion detector. It reduces the output or stops the unit when the room remains unoccupied. This feature can be useful in a zone whose use changes frequently, such as an office, guest room, or family room.
Smart control is beneficial, but it cannot compensate for incorrect sizing. Efficiency always starts with properly selecting the capacities, correctly positioning the indoor units, and carrying out the refrigeration installation according to the rules.
Mistakes to avoid when installing a multi-zone system on a roof
Our experience with projects in Saint-Constant, Montreal, Laval, Longueuil, on the North Shore and the South Shore enables us to identify several mistakes that can reduce the lifespan or performance of a heat pump.
Installing the unit directly on the membrane
A metal base or rigid support should not exert concentrated pressure directly on the roof. A load-distribution method and a protective layer are necessary.
Underestimating defrost water
A heat pump used for heating produces water during its defrost cycles. A unit that is too low may become surrounded by ice.
Blocking air discharge
A parapet, chimney, or another unit that is too close can cause air recirculation and reduce efficiency.
Choosing capacities based solely on floor area
Two rooms of the same size may have very different needs. Glazing, orientation, and insulation must be analyzed.
Neglecting line length
The airHome Multi range imposes minimum and maximum line lengths. For the dual-zone model, the documentation specifies a maximum total length of 165 feet, a maximum length of 82 feet between the units, a minimum length of 16 feet, and a maximum total elevation difference of 66 feet.
Forgetting service access
An appliance placed too close to an obstacle becomes difficult to inspect. The space needed to remove the panels must be maintained.
Assuming that both zones can operate in opposite modes
A single outdoor unit normally cannot heat one zone while actively cooling the other. This limitation should be understood before purchase.
A clean installation that also facilitates future maintenance
The quality of an installation is not measured only on the day it is commissioned. We must be able to return several years later to access the connections, clean the heat exchanger, check the pressures, or replace a component without unnecessarily dismantling the structure.
The elevated support visible in this Saint-Constant installation provides access beneath the unit and around the panels. The lines arrive without excessively tight bends. The fan remains unobstructed. The unit is positioned a reasonable distance from vents and other rooftop obstacles.
These details are not very visible from inside the building, but they directly affect reliability, noise levels, and the cost of future service calls.
A relevant solution for several types of properties on the South Shore
A dual-zone HITACHI airHome Multi heat pump may be suitable for several configurations:
- a house with an open ground floor and a primary bedroom;
- a duplex requiring two comfort zones within the same dwelling unit;
- a home with one floor that is warmer than the rest of the building;
- a business with two enclosed offices;
- a property with limited ground-level space;
- a building whose mechanical equipment is already grouped on the roof.
However, the roof is not automatically the best location. We also assess accessibility, structural considerations, noise transmitted to the building, line length, and winter maintenance conditions. In some cases, a wall-mounted or ground-level installation remains preferable.
AirGreen’s approach to a durable multizone heat pump
For every project, we strive to balance comfort, performance, and the building’s physical realities. This HITACHI airHome Multi multizone heat pump installation in Saint-Constant illustrates this approach well.
Choosing a dual-zone configuration makes it possible to condition two spaces separately. A rooftop installation frees up the outdoor areas used by occupants. The elevated support protects the membrane and improves clearance beneath the unit. The lines are insulated and organized. The location maintains sufficient airflow and reasonable access for maintenance.
An efficient heat pump can only reach its full potential when it is properly sized and installed. At AirGreen, we apply the same rigor to our wall-mounted air conditioner, multizone heat pump, central system, and HVAC installation projects throughout Greater Montreal, particularly in Montreal, Laval, Longueuil, Saint-Constant, the North Shore, and the South Shore.