Two new flat-roof units for a Montreal plex: winter performance, silence and clean installation by AirGreen
Context and objectives of the project
In a plex in Rosemont–La Petite-Patrie , the co-owners wanted to modernize their comfort without cluttering the facade. Our recommendation: two Sharp wall-mounted heat pumps (ZU1 series, R-32 refrigerant ) dedicated to separate zones, with condensers installed on the flat roof . The objective is twofold: stable air conditioning in the summer, efficient heating until the bitter cold in winter, while preserving the building's aesthetics.
Why the Sharp ZU1 series for Montreal
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Low GWP R-32 , more efficient than R-410A.
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Extreme cold design adapted to Greater Montreal winters.
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Very good noise level both outside and inside, ideal for dense areas (neighboring balconies, alleys).
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Reliability and locally accessible parts, a real plus for HVAC maintenance .
Reading the site: granulated roofs and clearances
The building has a gravel membrane with several outlets (chimneys, antennas, conduits). We note:
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Installation of the two condensers on weighted HDPE bases , aluminum rails and anti-vibration pads .
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Raised about 45 cm to clear blown snow and ensure good air circulation.
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Respect side and rear clearances for the flow, away from chimneys to avoid the suction of fumes and particles.
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Discreet routing of refrigerant lines and cables, sheathed and UV protected , running along the acroterion to the crossings.
Equipment selection and sizing
Each living area gets its own Sharp ZU1 unit. We size the BTU capacity from:
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The surface and orientation of the parts,
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Insulation (typical brick walls, roof),
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Summer solar gains and losses at −20°C and above.
Result: two single-zone circuits for fine modulation, appreciable redundancy and better seasonal efficiency than a single large, underutilized multi-zone.
Key Steps in HVAC Installation
1) Roof preparation and logistics
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Leveling of the bases on the gravel, addition of distribution slabs and retaining straps against gusts.
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Oriented layout to avoid cross-flow between units.
2) Drillings and crossings
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Waterproof cores with flashings and membrane-compatible mastic.
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Vapor barrier ducts inside, fire barriers on floors if required.
3) Lines and wiring
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Approximately 10 to 15 m per system between condenser and wall head.
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Continuous pipe insulation , tight taping, gravity routing for the interior drain to the exterior or the planned recovery point.
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Waterproof disconnect boxes installed within easy reach on the roof, dedicated 240V circuits from the panel.
4) Refrigeration procedures
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Nitrogen test and leak detection.
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Vacuum draw down to < 500 microns, stabilization.
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Adjust R-32 charge according to actual length.
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Start-up, superheat/subcooling readings and electrical checks.
Visible details that make the difference
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White rails placed on treated wooden bases and pads : limit the transmission of vibrations and protect the membrane.
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Neat grouping of connections in a black UV sheath: aesthetics and durability.
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Sufficient installation height for winter: the exchangers breathe even when snow accumulates on Montreal roofs.
Results for occupants
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Consistent comfort room by room thanks to inverter control .
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Very low noise outside: neighborhood preserved in the alleys.
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Significant energy savings compared to basic electric convectors.
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Possibility of integrating an optimized defrosting mode by programming according to habits.
Grants and Eligibility
High-performance R-32 wall-mounted heat pumps are generally eligible for provincial or municipal energy efficiency programs when they are open. We assist our customers to verify eligibility , prepare compliance photos , and complete forms as needed. As conditions may change, we perform a verification at the time of the quote .
Good practices and pitfalls to avoid on a flat roof
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Never place the units directly on the bass: always use bases/rails with anti-vibration.
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Avoid sucking in stale air (near vents, chimneys).
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Protect all connections against UV rays and shocks (feet, snow, tools).
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Provide a safe and clear service passage for maintenance .
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In winter: maintain a snow-free perimeter of 60 to 90 cm around the units.
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Inside: clean tappings , continuous slope for the drain (or condensate pump if necessary).
Maintenance recommended by AirGreen
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Clean the wall head filters every 2 to 3 months.
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Annual inspection: coils , fans , tightening of terminals, checking of static pressure and electronic parameters.
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Seasonal check of the bases , the sealing of the crossings and the UV sheath .
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At the start of winter: confirm the freedom of the grids and the condition of the pads .
Why entrust your HVAC installation to AirGreen?
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Local team accustomed to Montreal plexes , flat roofs and the peculiarities of alleys.
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Documented methodology (tests, photos, adjustment sheets) to ensure traceability and performance.
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Responsive after-sales service , available parts and suitable maintenance contracts .
Construction timeline (real Rosemont case)
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Technical visit and measurement: 60 minutes.
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Electrical validation (locations of disconnections, calibers).
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D-Day : delivery, installation of bases, drilling, drawing of lines, connections, refrigeration tests.
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Commissioning and occupant training (remote controls, modes, winter instructions).
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Sending of the end of work report with photos and parameters.
Comfort tips for summer and winter
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Summer: aim for 23–24°C continuously, Dry mode on humid days to reduce latent load.
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Mid-season: choose Heat mode with low ventilation for stable and quiet comfort.
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Winter: Keep units clear , schedule defrosts intelligently, and do not turn off power during periods of prolonged cold.
What if you're still hesitating between multi-zone and single-zone ?
In this building, two single zones offer:
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Better SEER/SCOP thanks to modulation closer to real needs.
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Redundancy : if one unit stops, the other takes over partially.
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Independent comfort per floor or per living area, useful in plexes.
AirGreen installs and maintains wall-mounted heat pumps throughout Montreal, Laval, Longueuil, the North Shore, and the South Shore . For a clear quote, up-to-date grant advice, and careful installation on flat roofs or facades, our team will assist you from design to commissioning.
Express FAQ
Q: Can we put a snow guard around the units?
A: On flat roofs, we prioritize height and clearance first. When the environment requires it, lightweight deflectors can be added without restricting airflow.
Q: Is there a risk of membrane overload?
A: Weighted bases distribute the load; we follow the roof manufacturer 's recommendations and, if in doubt, we validate the load-bearing capacity .
Q: Do I need a condensate pump?
A: Not always. When gravity draining to the outside or a disposal point is not possible, we install a silent pump with a flow limiter and alarm.
Conclusion
The Rosemont–La Petite-Patrie project illustrates a clean, sustainable and efficient integration of two Sharp ZU1s on a flat roof . The result: all-season comfort , acoustic discretion and infrastructure ready for Montreal winters. This is the AirGreen approach: technical, rigorous and designed for sustainability .