A flat roof installation designed for the Montreal climate: stability, silence and four-season performance
Background and objectives
In a typical plex in Southwest Montreal , the owner wanted to modernize the comfort of the main floor without encroaching on the interior space or the facade. We proposed a Gree wall-mounted heat pump ( R-32 refrigerant) with a condenser installed on a flat roof . The challenge: to combine performance , sound discretion and durability in the face of prevailing winds, freeze/thaw cycles and snow accumulations.
The selected equipment
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Type : wall-mounted heat pump (mini-split) , one indoor head for the open living area.
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Brand : Gree .
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Range : R-32 generation with high seasonal efficiency.
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Target capacity : 12,000–15,000 BTU depending on the main zone load calculation.
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Key advantages : inverter compressor, low temperature capacity maintenance, reduced noise level, optimized defrost electronics, low GWP of R-32 refrigerant.
HVAC Installation Details – Rooftop Condenser
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Support : raised aluminum frame anchored on anti-vibration pads . The loads are distributed via protective soles to protect the roof membrane.
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Clearance : clearance under the device to limit the suction of gravel , facilitate the flow of winter condensates and prevent snow drifts.
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Refrigerated connections : protected path in a chute up to the parapet , then crossing under a waterproof cover. Reinforced UV insulation and taping to counteract sunlight and wind.
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Cabling : power and communication combined in the same route with anti-drip loop; service reserve for future maintenance.
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Estimated total length **: 8 to 12 m between the indoor head and the condenser, ideal length for a good compromise between pressure losses and technical access.
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Waterproofing : roof passage and vapor barrier sleeve at the parapet; membrane-compatible mastic to prevent any infiltration.
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Upgrade : fine adjustment of the frame for the defrost flow , orientation in accordance with the prevailing wind direction to protect the exchanger.
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Safety and maintenance : free space all around the device (≥ 30 cm on the sides, ≥ 60 cm on the front) for easy access to the electrical cabinet, valves and fan.
The inner head: diffusion and comfort
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High ceiling installation to promote minimal stratification and the Coanda effect.
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Wide-angle motorized sweep to cover living room, dining room and open kitchen.
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Gravity drainage to the exterior: continuous slope, air trap and anti-vibration collars to prevent gurgling. No condensate pump required, reducing maintenance risks and noise.
Commissioning procedure
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Nitrogen test and leak test at flared fittings.
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Deep vacuum < 500 microns, stabilized with rebound monitoring.
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Opening of the valves , superheating and subcooling readings in cooling mode then in heating mode.
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Checking the intensities , calibrating the settings , pairing the remote control and explaining the modes to the occupant.
Construction site challenges and our solutions
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Flat gravel roof exposed to the wind: high-rigidity frame and high-density pads to prevent any drift. Orientation studied to limit air recycling and whistling from the fan.
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Parapet crossing : use of a rigid waterproof cover , complete UV protection of the cold insulation, sealed connections for a lasting result.
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Access and handling : secure ascent by ladder with lifeline , handling of the unit using straps to avoid marking the sheet metal.
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Noise perceived inside : anti-vibration spacers and service loops on the lines to mechanically decouple the unit from the walls.
Results obtained
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Uniform cooling in summer and efficient supplementary heating in the off-season and in winter.
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Silence on the roof and inside thanks to vibration decoupling.
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Aesthetics preserved : no projection on the front facade; installation invisible from the street.
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Efficiency : fine modulation of the inverter , reducing on/off cycles and consumption.
Good usage practices
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Stable setpoint (21–23°C) to allow the inverter to optimize power.
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Sweeping : in summer, flap slightly upwards to diffuse without drafts; in winter, horizontal sweep to mix the stratified air.
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Doors open to extend comfort to hallway and adjacent rooms.
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Dehumidification mode as needed to improve humidity comfort without overcooling.
Recommended HVAC maintenance
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Filters : Rinse every 4–6 weeks during heavy use.
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Internal exchanger and turbine : annual professional cleaning.
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Roof condenser : dusting of the fins, checking of the anchors , inspection of the roof passage seals after freezing/thawing episodes.
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Annual inspection : performance readings, terminal tightening, defrosting and flow control.
Grants and Eligibility
High-performance R-32 wall-mounted heat pumps may be eligible for assistance based on their nominal efficiency and low-temperature capacity maintenance. We validate each file for our clients in Montreal, Laval, Longueuil, North Shore, and South Shore , by providing the required technical evidence and installation certification.
Mistakes to avoid (feedback)
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Installing a condenser on the roof too low : risk of sucking up gravel/snow and hindering the flow.
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Forget about UV protection on insulation in direct sunlight.
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Undersize capacity for an open living area.
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Neglecting deep vacuum and leak testing : major causes of early failures.
Why this solution for the Southwest?
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Urban density and flat roofs : roof installation frees up interior courtyards and respects the aesthetics of the alleyways.
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Local climate : defrosting electronics and inverter modulation provide stable comfort, even during cold snaps and thaws.
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Maintenance : generous clearances and clear paths facilitate maintenance, ensuring longevity.
Site sheet — summary
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Address : Le Sud-Ouest sector (Montreal) , flat-roofed plex.
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Appliance : Gree R-32 wall-mounted heat pump , 12–15k BTU depending on load.
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Condenser : on raised frame with anti-vibration pads, protective soles, wind orientation .
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Route : gully connections to the parapet , watertight crossing; length ~8–12 m.
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Internal drain : gravity ; no condensate pump .
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Commissioning : deep vacuum , nitrogen test, thermodynamic measurements, fine adjustments.
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Goal : four-season comfort with durable and discreet HVAC installation .
Need a similar project?
We size, install and maintain wall-mounted heat pumps on flat roofs or facades, according to the best practices of Greater Montreal . We intervene quickly in Montreal, Laval, Longueuil, North Shore and South Shore with complete support (selection, installation, HVAC maintenance , grant application).