A flat roof installation designed to last: snow management, membrane protection and optimized refrigerant path.
Context: a Plateau plex, four-season comfort and roof access
At AirGreen , we are modernizing the comfort of an apartment in Plateau-Mont-Royal . The indoor unit is wall-mounted (single-zone) and the condenser is installed on the flat roof typical of Montreal plexes. The occupants' priorities: stable heating in mid-season and winter , quiet air conditioning in summer , and an installation that respects the roof membrane while remaining easy to access for maintenance.
We are choosing a Midea28 (R-454B) with 12,000 to 18,000 BTU depending on the load, appreciated for its heating range down to −30 °C , its fine modulation and its high seasonal efficiencies. This generation reduces the environmental footprint compared to R-410A and meets the criteria of Quebec assistance programs when the efficiencies are there.
Implementation strategy: a raised, protected and stable condenser
Membrane supports and protection
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Installation of a structure on EPDM pads with a large support surface, in order to distribute the loads without puncturing the elastomer membrane.
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Precise timing and leveling to ensure proper flow of defrost water and avoid any unwanted vibration.
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Interposition of a geotextile and inspection of the membrane before/during/after the work.
Clearances and air circulation
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Peripheral clearance respected for suction/discharge (side brick wall and parapets taken into account).
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Orientation of the discharge away from air stagnation areas and rainwater inlets, in order to optimize COP in winter and SEER in summer.
Snow and Ice Management
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Raising the condenser for winter defrosting; creating a flow path to the roof drain.
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Addition, if required by the exposure, of a snow guard and a deflector to prevent burial during accumulations.
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Checking access guardrails and anchor points to enable safe maintenance.
Refrigerant path: short, protected and maintainable
Lines and insulation
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Short to medium line lengths from the interior head to the roof; controlled bend radii to preserve compression and limit pressure losses.
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Continuous insulation of both lines with closed cell foam, UV tape and clear paint on exposed sections to reduce solar absorption.
External chute and sealing
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Use of an exterior grade UV chute up to the flashing; continuous slope for gravity drainage of condensate from the indoor unit.
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Single penetration with mechanical flashing and roof -compatible vapor barrier ; sealed with non-shrinking mastic to maintain air and water tightness.
Electricity and control
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Dedicated circuit to the panel, circuit breaker rating prescribed by Midea; service switch near the condenser.
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Cable routing in the duct, stainless steel fixings and expansion loops for resistance to thermal cycles.
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Complete polarity and grounding test before commissioning.
Commissioning: what we systematically check
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Nitrogen pressure testing and flush brazing to prevent internal oxidation.
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Deep vacuum until target pressure is reached and vacuum gauge stability is achieved .
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Control of superheat/subcooling , blowing temperatures , intensities and pressures in cooling and heating modes.
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Adjust the shutters and flow rate to prevent drafts in the living room; educate occupants on Auto/Heat/Cool modes and timers.
Result for the occupants
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Quiet and consistent : the Midea28 low module for mid-season, ideal for teleworking and quiet nights.
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Winter comfort : maintains good capacity down to −30°C , useful during Montreal cold spells.
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Durable finish : intact membrane, cushioned supports, UV-protected lines — the basis of an installation that lasts over time.
AirGreen Best Practices on Montreal Flat Roofs
To do
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Raise the condenser above the snow plane.
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Direct the defrost water to the drain; if necessary, provide a retention tank or drainage trench .
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Protect the refrigerant insulation from the sun and wildlife (birds/squirrels).
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Plan access : secure ladder, circulation path, clearance around the unit for maintenance.
To avoid
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Lay directly on aggregate or on bare wood which may retain moisture or mark the membrane.
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Too long line paths with unnecessary loops that penalize performance.
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Internal condensate pumps not essential (source of noise and maintenance) when gravity is possible.
Sizing and capacity selection
In the Plateau plexes, the envelope is often renovated but the internal gains (kitchen, south-facing windows) are marked. A 12 kBTU is often sufficient for an open living room-kitchen; an 18 kBTU is retained if the volume also serves a corridor or an adjacent bedroom. Our load calculation considers the orientation, the glazing and the sealing, then validates the modulation range so that the machine operates most of the time at low speed .
Grants and Eligibility
High-efficiency wall-mounted heat pumps using R-454B/R-32 may be eligible for assistance programs depending on certified performance and installation method. We prepare technical data sheets and installation certificates for applications in Montreal , Laval , Longueuil , the North Shore and the South Shore .
HVAC Maintenance: Keeping Performance at Peak
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Filters : monthly rinsing during periods of use; replacement/maintenance depending on condition.
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Annual inspection : electrical tightening, leak test, verification of supports and chute.
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Roof : clearing drains , removing debris around the condenser, checking after episodes of high winds.
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Winter : Ensure that defrost water does not freeze around the unit; maintain a clear path.
Construction site technical sheet
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Type : single-zone wall-mounted heat pump
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Brand/Range : Midea28 (R-454B)
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Installation : flat roof on EPDM pads, free discharge orientation
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Route : short lines, UV insulation, external trunking, sealed holes
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Condensate : gravity for the indoor unit; free defrost drain on the roof
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Compliance : dedicated circuit, service switch , pressure + deep vacuum tests
And for you?
Whether you are in Plateau-Mont-Royal , Villeray , Verdun or on the South Shore , we design robust and careful HVAC installations — on walls, floors or flat roofs — with one obsession: lasting comfort and a preserved roof .