A flat roof heat pump designed for the Montreal climate and mansard-roofed buildings
At AirGreen , we regularly work on plexes in the Plateau-Mont-Royal with flat roofs and skylights. This configuration, emblematic of Montreal, requires a rigorous HVAC installation to guarantee efficiency , silence and durability in all seasons. On this project, we are installing a Midea wall-mounted heat pump (new R-454B range , high performance in cold weather) with the condenser positioned on the roof to free up the facade and ensure optimal air circulation.
Architectural context: flat gravelled roof, dormers and acroteria
The building has a flat roof covered with gravel , glazed skylights facing the courtyard and a peripheral metal acroterion . This type of envelope requires special precautions:
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Compliance with permissible loads and distribution of supports on the membrane.
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Preservation of waterproofing (no punching, no friction).
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Management of service roads for future maintenance.
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Control of defrost discharges in winter to prevent ice from forming near skylights.
Our mission: to integrate the heat pump without altering the roof or compromising access security.
Why Midea (R-454B) for a Montreal plex?
In the family of new generation wall-mounted heat pumps , the Midea R-454B stands out for:
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An inverter compressor that finely modulates power to maintain a stable temperature.
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High seasonal yields and excellent cold weather performance, suitable for Greater Montreal winters.
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A new generation refrigeration (R-454B) with low GWP, meeting evolving standards.
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Quiet operation thanks to the fan and optimized acoustic profile.
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A wide capacity range (9k to 24k/33k BTU) covering apartments and full floors.
This choice allows you to combine four-season comfort , energy savings and eligibility for efficiency programs often available in Montreal, Laval, Longueuil, on the North Shore and the South Shore (depending on the final configuration and the criteria in force).
Roof installation methodology
1) Technical study and implementation plan
We begin with an inspection of the roof : condition of the membrane, slope, drainage points, obstacles (skylights, vents, parapets). We then validate:
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The necessary blowing template around the condenser (side and top clearances).
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The route of the refrigeration connections to the interior head (as direct as possible to limit losses).
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Electrical proximity for a secure and aesthetic connection.
2) Supports without membrane perforation
The condenser is placed on an aluminum frame fixed to distributor pads mounted on wooden soles protected by SBS/puncture-proof self-adhesive strips. This assembly:
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Prevents membrane perforation .
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Distributes the load over a sufficient area.
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Facilitates unit leveling and alignment.
Anti-vibration spacers limit the transmission of vibrations to the structure.
3) Refrigerant connections and condensate management
The copper pipes are insulated along their entire length with a UV-resistant sheath , reinforced with butyl tape in the areas of direct exposure. The route runs along the acroterion, then descends towards the technical duct. Condensates are managed by gravity to the planned evacuation area, with a continuous slope, anti-float collars and frost protection on the exposed segments.
4) Outdoor electrical connection
A waterproof disconnect box is installed near the unit, at working height. The power cable follows a protected route, fixed at regular intervals, with a rain loop before penetration.
5) Commissioning
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Deep vacuum , stabilization and leak test.
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Check for superheat/subcooling .
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Acoustic and vibration control.
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Validation of air flow rates and calibration of the remote control.
AirGreen Project Challenges and Responses
Exposure to winds : the roofs of the Plateau are more exposed. We secure the whole thing by bracing the frame , checking the tearing forces and positioning it along the acroterion to break the wind.
Proximity to skylights : to avoid any recycling of hot air towards the windows and to preserve the peace of mind of the occupants, the unit is offset and oriented so that the blowing is free and directed towards an open area.
Defrost management : In winter, the unit periodically switches to defrost. We install an outlet away from the pathways, preventing ice from forming near the skylights and the access ladder.
Waterproofing : Each contact point is protected by interface strips to avoid damaging the membrane. No through-anchoring is carried out without agreement and waterproofing details.
Inside: precise comfort and sobriety
The Midea wall head associated with this condenser finely regulates:
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Rapid rise in summer to lower the temperature smoothly.
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Stable maintenance in intermediate heating and extreme cold, thanks to the inverter.
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Adjustable filtration and blowing direction to avoid drafts.
The noise level is contained to respect the tranquility of the living areas. The result: uniform comfort , particularly appreciated in the typical dual-aspect accommodation of the Plateau.
Best practices specific to Montreal flat roofs
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Clearances : Maintain clear space around the condenser for maintenance and air circulation, away from snow edges.
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Service path : mark out a path (slabs or compacted gravel path) to avoid damaging the membrane during maintenance visits.
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UV protection : use black/UV insulation on the connections and renew the sleeves if necessary.
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Reasonable snow removal : gently clear the area around the unit after heavy snowfall without piling the snow against the condenser.
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Spring monitoring : when thawing, check the flow of condensate and the condition of the pads.
These points, systematically applied by our teams, extend the lifespan of the installation and preserve the watertightness of the roof.
HVAC Maintenance: What We Do Every Year
AirGreen offers targeted annual maintenance for rooftop installations:
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Cleaning of the batteries (internal/external) and checking of the fins.
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Checking pressures , load and inverter settings.
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Electrical control (tightening, circuit breaker, proximity circuit breaker).
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Inspection of the chassis , distribution pads and membrane interfaces.
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Defrost and flow test; slope correction if necessary.
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Updated usage recommendations based on weather history.
This maintenance guarantees energy performance and limits seasonal breakdowns .
Measurable results for the owner
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Energy savings compared to electric baseboard heaters or a window air conditioner.
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Four-season comfort covering the essentials of mid-season heating and summer air conditioning.
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Controlled noise : the rooftop location, away from the bedrooms, improves acoustic comfort.
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Preserved facade : no influence on the exposed masonry on the street side.
AirGreen Expert Advice Before Choosing a Rooftop Installation
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Check access (trapdoor, ladder, guardrail). Access determines safety and maintenance costs.
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Anticipate the route of the connections: the shorter and more direct it is, the better the performance .
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Analyze the roof with an HVAC inspection: slopes, valleys, drains, shaded areas and snow accumulation.
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Planning for winter : location and management of defrost water to avoid ice patches.
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Choose a range adapted to cold weather : Midea's new generation R-454B wall-mounted heat pumps offer excellent resistance to low temperatures, making them ideal for Montreal.
AirGreen: local support throughout Greater Montreal
Our teams operate weekly in Montreal, Laval, Longueuil , as well as on the North Shore and South Shore . We are experts in the specificities of Montreal's flat roofs , from the narrow streets of the Plateau to buildings in central districts . Each project benefits from tailored installation engineering , precise thermal calibration , and documented commissioning .
In short
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Equipment type : Midea wall-mounted heat pump ( R-454B range, high efficiency).
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Installation : condenser on flat roof , aluminum frame, pads on protected soles, UV insulated connections.
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Location : Plateau-Mont-Royal (Montreal) .
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Key advantages : four-season comfort, controlled consumption, intact facade, easy maintenance.
For a similar project or to assess the feasibility of an HVAC installation on a flat roof, our team will advise, size and install with the rigor that AirGreen is known for.