Condenser on a flat roof, raised for snow: a robust installation designed for Montreal's extreme cold
At AirGreen , we deployed a Sharp ZU1 series wall-mounted heat pump, R-32 refrigerant, Inverter in the heart of Villeray–Saint-Michel–Parc-Extension . The outdoor unit is installed on a flat roof and mounted on a raised support , to ensure reliable operation in winter and safe service access . The objective: to offer the customer stable heating at low temperatures and precise air conditioning in summer, without compromising on the durability or waterproofing of the roof.
The building and its climatic constraints
The accommodation is located in a typical plex of the area, with flat roofs, low acroteria, and various obstacles (air intakes, vents). In winter, the site experiences snow drifts and crosswinds that move powder snow. We designed the layout to:
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maintain large clearances around the condenser (faces and top),
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raise the device ~65–75 cm from the roof plane to stay out of the accumulation zone ,
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preserve the membrane and the building envelope ,
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simplify HVAC maintenance visits in all seasons.
Why the Sharp wall-mounted heat pump (R-32) here?
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Inverter technology : fine modulation, optimized consumption and silence .
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R-32 : better seasonal efficiency and lower GWP than older generations.
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ZU1 series extreme cold range : capacity maintenance when the mercury drops, adapted to the climate of Montreal , Laval and the North Shore/South Shore .
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Ideal compactness for installation on a raised roof frame .
Flat roof installation engineering
Galvanized raised support
The condenser rests on a galvanized steel frame with adjustable feet and anti-vibration pads . Distribution pads protect the membrane. This architecture:
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keeps the exchanger above snow and defrost water ,
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limits the suction of powder which clogs the fin,
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prevents encapsulating frost on the ground and stabilizes defrost cycles.
Lashing & sealing
The anchoring takes into account wind loads . The holes are treated with compatible flashings , appropriate mastication and reconstruction of the vapor barrier on the interior side. The structural fixings are bridged on load-bearing elements to avoid stressing the membrane.
Standard clearances and airflow
The unit is oriented to prevent air recirculation toward parapets/obstructions. Top and side clearances exceed the manufacturer's recommendations to ensure flow and heating capacity .
Refrigerated journey and crossings
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Short path from the interior technical column to reduce losses and fluid load.
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High-density continuous insulation , UV-stable outdoors, without thermal bridges .
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Waterproof roof passage with controlled slope , fire-resistant foam if required and clean finish on the ceiling side.
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Waterproof outdoor disconnect switch installed within easy reach for maintenance.
Frost, snow and wind management
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Snow-drift height : the free space under the unit allows defrost water to drain away without forming blocks of ice.
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Drainage path under the chassis to prevent accumulation and deformation of the support.
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Openwork snow guard (optional) if the building has recurring vortices depending on the wind orientation.
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Lightweight windbreak (optional) in case of extreme exposure, sized so as not to penalize static pressure .
Inside: wall-mounted headboard and discreet finishes
The wall-mounted head is placed high under the ceiling in the living area, clear of any obstacles. The connections follow a discreet white capping up to the crossing point. The installation respects the gravity slope of the condensate drain; if the configuration requires it, we offer a silent lifting pump integrated into the chute.
Commissioning: AirGreen method
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Brazing under nitrogen to protect the inside of the tubes.
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Nitrogen proof and deep vacuum (stable microns).
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Refrigerant opening and superheat/subcooling control.
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Heating tests in winter conditions: intensity, modulation, noise level and defrosting .
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Electrical checks : tightening torque, polarities, operation of the disconnector .
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Handing over instructions : optimal winter/summer use, HVAC maintenance and roof maintenance around the unit.
Results obtained
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Stable heating in cold weather thanks to inverter modulation.
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Reduced noise perceived in the home and from neighbors on adjacent roofs.
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Simple and secure service access , limiting the duration of interventions.
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Aesthetics respected on the roof, clean clearances and protected membrane .
Good practices and pitfalls to avoid
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Never place the unit directly on the membrane : ice forms and performance collapses.
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Avoid lines that are too long : favor a direct and isolated route , otherwise capacity will be lost.
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Refuse improvised roof passages : only suitable flashing guarantees longevity.
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Always allow 60–80 cm of free space around the unit after each storm.
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Clean the inner head filters every 6–8 weeks in season.
Recommended maintenance
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Annual inspection : exchanger cleaning, checking defrost cycles , electrical check, mechanical tightening, condition of flashings and chassis .
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Spring : visual inspection of the installation (pads, galvanized paint, screws).
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Winter : Gentle manual clearance around the chassis (no metal tools near the finning).
Key project data
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Type of equipment: wall-mounted heat pump (mini-split) .
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Brand/Range: Sharp – ZU1 series , R-32 , Inverter .
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Exterior installation: flat roof on raised galvanized support with anti-vibration pads .
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Clearance height under unit: ~ 65–75 cm .
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Cooling path: short , continuous UV-stable insulation.
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Power supply/control: waterproof disconnect switch nearby, protected sheath.
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Condensate/defrosting management: dedicated under-chassis drainage, area cleared of snow after storms.
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Compliance: CSA/RBQ best practices, CNESST working at height safety.
Grants and support
High-efficiency wall-mounted heat pumps may be eligible for assistance programs in effect in Quebec, subject to certified performance and cold climate performance . We support our customers in Montreal, Laval, Longueuil, North Shore and South Shore : eligibility validation, complete file , and quote .
Conclusion
This project in Villeray–Saint-Michel–Parc-Extension illustrates our approach: predicting snow , protecting the envelope , optimizing airflow and delivering a clean, durable and easy-to-maintain HVAC system . The Sharp ZU1 now provides four-season comfort with tangible energy savings for the customer.