A flat roof installation designed to last, without compromising on performance or aesthetics
At AirGreen , we design each HVAC installation based on the building and the occupants' lifestyle. In this typical Villeray–Saint-Michel–Parc-Extension duplex, we are installing a new-generation GREE wall-mounted heat pump with R-32 refrigerant , with the outdoor unit installed on the flat gravel roof . The goal: to ensure four-season comfort in Montreal while preserving interior tranquility and the integrity of the building envelope.
Project context: four-season comfort and urban constraints
The owner wanted a solution:
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Quiet , so as not to disturb the backyard or the neighbors;
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Effective in Montreal winters , maintaining heating capacity in cold weather;
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Discreet , avoiding a visible unit in the alley or on the terrace;
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Easy to maintain , despite ladder access to the roof.
Taking these priorities into account, we recommended a GREE R-32 wall-mounted heat pump (model from the recent range) , known for its stable performance at low temperatures , its energy efficiency and the rapid availability of parts in Quebec.
What we implement on a Montreal flat roof
Support structure and membrane protection
The outdoor unit is raised on an aluminum base placed on two load-bearing pads with protective soles. This configuration:
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Distributes the load on the gravel and membrane;
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Adds 30–40 cm of ground clearance , limiting snow accumulation and allowing water to drain away;
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Reduces vibration transmission thanks to elastomeric interfaces;
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Facilitates annual inspection and frost/thaw removal in heating mode.
Refrigerated and electrical transport
The refrigeration lines and the electrical supply run through a watertight roof passage with a protective collar and cap, away from the edge to prevent water backflow and wind lifting. We favor:
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Soft elbows and continuous insulation (high density cellular) to limit losses;
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UV sleeved on all exposed sections;
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Vapor barrier strip at each penetration of the envelope;
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Wiring in sheath with weather stripping for resistance to frost and sunlight.
Condensate management, winter and summer
On a flat roof, the challenge isn't just in the summer. In heating mode , defrost cycles produce water. We plan:
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Gravity drain to a roof drainage area;
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Clearance under the unit to prevent re-icing on the exchanger;
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Heating wire option on request when the environment is particularly windy or shaded.
Wind safety and maintenance access
Montreal experiences sustained gusts , especially along the edges of built-up areas. The base is anchored and braced according to the manufacturer's recommendations and local best practices. We maintain peripheral clearance for airflow and maintenance, and we define an access path (step tiles or protection panel) to preserve the membrane during maintenance visits.
Why a GREE R-32 wall-mounted heat pump for this project in Villeray?
Cold climate performance
GREE R-32 wall-mounted ranges offer reliable heating below zero , with fine modulation of the inverter to maintain comfort without overconsumption. In air conditioning, the equipment displays an advantageous COP/SEER , ideal for a medium-sized Montreal home.
R-32 Refrigerant: Efficiency and Responsibility
R-32 reduces GWP (Global Warming Potential) compared to older R-410A fluids and improves heat exchange , resulting in:
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Lower consumption ;
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Stable capacity in cold weather;
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Easier eligibility for current aid programs when performance criteria are met.
Acoustic comfort and durability
The GREE wall-mounted unit design incorporates a balanced external fan and electronic speed control . Combined with our detached bracket, these elements provide a very low noise level , which is appreciated on roofs where reverberation is high. Exposed components (casing, screws, connections) receive an anti-corrosion treatment suitable for freeze/thaw cycles.
The installation process: our key steps
1) Survey and preparation
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Checking the structure (admissible load, condition of the membrane, drains).
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Choice of positioning : away from kitchen/bathroom outlets to avoid grease and vapors; sufficient clearance around the exchanger.
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Definition of the shortest interior route to the wall head and the roof passage .
2) Setting up the support
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Load-distributing bearing pads , placed on protective soles;
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Anchored anti-corrosion aluminum frame ;
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Checking the level to optimize condensate flow.
3) Refrigeration connection and vacuum drawing
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Cutting, flaring and fittings to the prescribed tightening torque;
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Deep vacuum and extended leak test;
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Refrigerant charge validated according to the actual length of the lines.
4) Commissioning and adjustments
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Testing of hot/cold modes , measurement of temperature and intensity differences;
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Setting speeds , inverter steps and checking sensors ;
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Customer advice: filter maintenance , clearance around the unit, maintenance plan .
Results: comfort, silence and measurable savings
From the very first cycles, thermal stability and rapid temperature rise confirm the correct sizing. Residents benefit from responsive air conditioning in the summer and efficient heating even in the cold periods of Montreal's winter. The rooftop installation frees up floor space and protects the unit from impacts and deposits from the alley.
Grants and compliance: what we systematically check
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Potential eligibility for aid ( Montreal, Laval, Longueuil, North Shore, South Shore ) according to the power , seasonal performance and extreme cold thresholds of the installed range;
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Electrical compliance (dedicated circuit breaker, disconnect within reach, cable gauge) and RBQ/CSA standards ;
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Documentation provided for reimbursement files and professional installation certificate.
Practical tips for Montreal flat roofs
Good practices to remember
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Minimum clearance around the unit (blowing/suction) and sufficient height for snow;
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Distance from hood outlets and vents;
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Non-slip service path to limit membrane wear;
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Pre-winter inspection : tightening of anchors, checking of insulation and collars;
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Annual HVAC maintenance by a certified technician to preserve the manufacturer's warranty.
Mistakes to avoid
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Place directly on the membrane without load distribution ;
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Neglect the direction of the prevailing winds and the turbulence generated by the walls;
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Allow defrost water to stagnate under the unit in winter;
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Forget about disconnect and maintenance clearances .
The AirGreen commitment
Our specialized HVAC installation teams in Montreal work weekly on duplex and triplex flat roofs . Our method prioritizes: cleanliness of the layout , quiet operation , accessibility for maintenance , and energy optimization . With a correctly sized GREE R-32 heat pump , your home becomes more comfortable , and your bills benefit.