The context: flat-roofed building, technical access and requirement for silence
In a building in Mercier–Hochelaga-Maisonneuve, our client wanted a compact HVAC solution to air condition living areas on the top floor, with reliable heating backup during the off-season. The choice of a GREE (R-32) wall-mounted heat pump was obvious: a discreet indoor unit for daily comfort and an outdoor condenser neatly installed on the flat gravel roof , away from air intakes and obstacles.
Why GREE in R-32 for this project
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Efficient inverter compressor and fine modulation at low load.
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R-32 refrigerant: better heat transfer, lower charge at equivalent capacity.
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Good capacity maintenance in negative temperatures usual in Montreal .
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Wide range 9k–24k BTU suitable for condos and plexes; precise selection after load calculation (surface area, windows, orientation, infiltration).
Rooftop installation: stability, waterproofing and durability
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Rail supports with anti-vibration blocks: load distribution without puncturing the coating.
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Clearances respected around the exchanger for optimal air sweeping and efficient defrosting in winter.
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Waterproof technical path (roof passage) for refrigeration lines and power supply, with vapor barrier recovery and membrane-compatible sealing.
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Outdoor disconnect switch box in a weatherproof enclosure, within easy reach for maintenance and compliant with local electrical requirements.
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Protected line routing in a UV trunking to the interior descent; the bend radii are respected to preserve the flares and avoid any stress on the fittings.
AirGreen commissioning: documented protocol
We apply a rigorous protocol, identical to our sites in Montreal , Laval , Longueuil , North Shore and South Shore :
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Nitrogen leak test (controlled high pressure) with zero loss recording.
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Deep vacuum draw down to < 500 microns then stabilization (ascent test).
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Opening the valves and weighing/adjusting the charge if the refrigeration length deviates from the factory charge.
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Start-up and measurement log : pressures, intensity, inlet/outlet temperatures, ∆T at the blower outlet, defrost mode control.
Condensate path: reliability first
Drainage is designed using gravity when the geometry allows (continuous slope from the interior head to the discharge point). When the architecture requires a rise, we add a silent condensate pump with a safety tank and alarm. The goal: zero overflow, even during intense dehumidification .
Noise and vibrations: neighborhood preserved
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Anti-vibration pads on the rails and controlled hose tension to prevent any structural transmission.
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Fan orientation and distance from neighboring equipment to reduce air recirculation and noise felt on the terrace.
Capacity selection and comfort achieved
On this type of housing, the target power is generally between 12,000 and 18,000 BTU depending on the load calculation . Result obtained after adjustments:
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Even cooling of living spaces, without “cold snaps”.
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Efficient heating support in spring/autumn, with modulation to avoid short cycles.
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Controlled consumption thanks to the high seasonal efficiency of GREE models in R-32 .
What we particularly look out for on a flat roof
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Walking paths and winter maintenance: clearing snow around the condenser to preserve the air intake.
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Water management : positioning outside runoff path, anti-tilt wedges.
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UV protection for insulation and cables; stainless steel clamps and tape adapted to the climate.
Electricity and compliance
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Dedicated circuit from the panel with suitable circuit breaker, cold climate rated outdoor cable, and proximity disconnect switch .
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Check polarity/ground and tighten to the correct torque on terminal blocks.
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Documentation provided to the customer: single-line diagram, nameplates, serial number, commissioning records.
HVAC maintenance: maintaining performance
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Inner head filters : Clean every 4–6 weeks during use.
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Annual inspection by AirGreen: pressures, intensity, ventilation, drain control, coil cleaning and parameter updates.
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On the roof: check the fixings , condition of the membrane around the roof passage and clear any obstacles.
Pitfalls to avoid (feedback)
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Leaky air barrier opening : condensation and odors — we systematically restore the seal.
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Excessive refrigeration lengths without charge recalibration: declining efficiency — we adjust the charge and validate superheat/subcooling .
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Air recirculation in a hidden facade: capacity losses - hence our studied clearances and orientations.
What the customer gains in Hochelaga-Maisonneuve
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Four-season comfort with a recent R-32 heat pump .
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Discreet rooftop installation that frees up the facades and respects the aesthetics of the building.
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Measured and archived commissioning for seamless monitoring.
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Easy access for HVAC maintenance , ensuring longevity and low operating costs.
What about subsidies?
Depending on the chosen configuration and the presence of efficiency certifications (e.g., ENERGY STAR for extreme cold for certain power levels), this type of installation may be eligible for assistance in effect in Quebec. We validate eligibility and, where applicable, include the required certifications in the file.
Areas served : Montreal , Laval , Longueuil , North Shore , South Shore .
Need technical advice for a flat roof or condominium ? Our team sizes, installs, and maintains your GREE wall-mounted heat pump with a documented and transparent approach.