Two condensers on a flat roof for controlled comfort, summer and winter
Context: a typical Montreal plex with a flat roof
In this mandate carried out in Rosemont–La Petite-Patrie , we are installing two Sharp outdoor units on a flat gravel roof of a plex. Objective: to ensure efficient heating and stable air conditioning for two dwellings, without noise or impact on the facade. The urban configuration requires vertical cooling paths via technical chimney , accessibility constraints and particular attention to the roof's waterproofing .
Why Sharp for this project?
Sharp 's Eco Inverter range is renowned for:
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fine modulation thanks to the inverter compressor (constant comfort, fewer on/off cycles);
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low noise level in continuous operation, crucial in dense environments;
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clear service accessibility (panels, valves, fittings) facilitating HVAC maintenance ;
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a robust design suitable for Montreal winters when properly sized and configured.
The selected capacities cover the usual needs of wall units for two 4.5–5.5-room dwellings. We always validate the capacity based on a load calculation (orientation, insulation, infiltration, glazing) in order to avoid under- or over-sizing.
Rooftop installation: stability, vibration, wind
Supports and anchors
Each condenser rests on an aluminum frame mounted on distribution pads (HDPE bases) and treated beams . This combination:
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distributes loads and protects the roof membrane ;
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limits the transmission of vibrations thanks to the silent blocks ;
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facilitates leveling to meet frost/defrost drainage clearance .
Air releases and recirculation
We maintain front and side clearances above the manufacturer's minimums to ensure good suction/discharge . The two condensers are spaced apart to avoid recirculation of hot air (winter) and to preserve full capacity during heat waves.
Wind and climatic loads
On an unobstructed roof, wind shear can cause resonances. Tightening to the prescribed torque, adequate silent blocks and the mass of the pads guarantee resistance to gusts . The passage of winter (snow, frost, defrosting) is anticipated by sufficiently raising the units.
Refrigeration connections and clean routing
The route follows the existing technical duct to the interior heads. The refrigerant lines (liquid/gas) are continuously insulated, protected and fixed at regular intervals to prevent buckling. The cumulative length per dwelling is average (≈ 12–15 m) , optimized to limit pressure losses and maintain high seasonal efficiency . The perforations are sealed with flashing and membrane-compatible sealants.
Electrical management and security
Each unit has its own dedicated circuit from the apartment panel, with a sealed external disconnect near the condenser. The wiring is installed in UV conduits and secured to ensure safe access during maintenance. Clear circuit labeling simplifies future maintenance.
Drainage, frost and “life on the roof”
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Defrosting : Water flows freely between the pads, away from stagnation areas, to prevent ice from forming around the support feet.
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Maintenance : Clearances allow gentle washing of the exchanger, checking of valves and pressure control without moving the equipment.
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Neighborhood : choosing a flat roof moves the sound source away from the windows, which improves acoustic perception inside.
Result for the occupants
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Uniform temperature in the main rooms; better controlled humidity in summer.
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Minimal noise pollution thanks to the inverter and rooftop installation.
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Low visual impact on the facade, criteria often appreciated by co-ownership syndicates .
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Easy maintenance: everything is accessible, marked, secure.
AirGreen Method: from submission to commissioning
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Thermal study of each dwelling (insulation, windows, internal contributions).
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Choice of capacity (9,000 to 18,000 BTU wall-mounted depending on the room and orientation) and verification of electrical compatibility.
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Layout plan : supports, routes, drilling, layout of fixings so as not to compromise the membrane.
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HVAC installation : nitrogen brazing, deep vacuum , leak testing, filling and setting of electronic cards (ventilation levels, defrost temperatures).
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Instrumented commissioning and submission of a report (photos, values, circuit numbers).
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Tips for using modulation (stable settings, auto mode avoided in winter, filter maintenance).
Best practices specific to Montreal flat roofs
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No unnecessary perforation : we reuse existing waterproofing paths and upstands where possible.
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UV protection on exposed connection insulation.
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Curvature radii respected to avoid micro-cracks and loss of performance.
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Manage cables away from drains and snow accumulation areas.
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Durable marking (engraved labels) to clearly identify each piece of equipment per dwelling.
Recommended Maintenance (and Why It Pays)
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Clean the internal filters every 4–8 weeks during use.
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Annual inspection : washing the external exchanger, checking connections, verifying operating pressures and temperatures, updating parameters if necessary.
Regular HVAC maintenance maintains performance and reduces electricity consumption throughout the life cycle.
Grants and Eligibility
Several high-efficiency wall-mounted heat pumps —including recent versions using new-generation refrigerants and certified for extreme cold —may be eligible for assistance programs. Eligibility depends on the indoor/outdoor unit pair and its certification. Upon submission, we confirm the amounts available for Montreal , Laval , Longueuil , the North Shore , and the South Shore .
Common Mistakes to Avoid (and What We Do Differently)
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Undersized supports : vibrations, noise, premature wear. → We size the structure and silent blocks according to load and wind.
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Air recirculation between two nearby machines. → Clearances greater than the minimum + orientation studied.
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Routes that are too long or have tight bends. → Optimized routes, reduced pressure losses.
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Neglected waterproofing on flat roof. → Flashings, compatible mastics, visual checks and photos at the end of the work.
What if your building looks like this?
Whether you're looking for a flat-roofed plex, a condo with a service duct, or a small rental building, we design and install your heat pump or wall-mounted air conditioner with the same meticulous care. Our team covers the entire Greater Montreal area and responds quickly to energy upgrades for existing buildings.
AirGreen, a trusted partner
Every day, we deliver clean, documented, and durable HVAC installations in Montreal , Laval , and Longueuil , as well as on the North and South Shores . Need an estimate for your flat roof or condominium? We come, we measure, we propose—and we install.