On a condo rooftop terrace: a clean, safe HVAC integration ready for our winters
At AirGreen , we regularly work in Montreal condominiums where floor space is scarce and facades are protected. This project, carried out in a contemporary building in the Lachine sector, illustrates a rooftop HVAC installation : a Midea wall-mounted heat pump – R-454B extreme cold range designed to provide stable comfort year-round, while respecting the roof membrane and condominium standards.
The technical choice: Midea R-454B for efficiency and extreme cold
Here we are choosing a Midea wall-mounted heat pump of the new generation using R-454B , a refrigerant with low GWP and excellent seasonal efficiency. This cutting-edge technology is essential for three major reasons:
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Low temperature heating performance : the inverter compressor and defrost electronics provide sustained power in negative temperatures, ideal for the exposed shores of Greater Montreal .
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High energy efficiency (SEER/HSPF higher than previous generation R-410A), meaning savings on bills and a reduced carbon footprint.
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Eligibility for municipal and provincial support programs when efficiency criteria are met — a real asset for co-owners in Montreal, Laval, Longueuil, North Shore and South Shore .
We size the capacity (9,000 to 18,000 BTU depending on common cases in condos) from a load calculation taking into account the orientation, the glazed surface, air infiltration and the insulation of the roof slab.
Context: co-ownership, shared spaces, TPO/EPDM membrane to be protected
Flat condo roofs impose strict rules: no uncontrolled penetration, protection of the membrane , respect for access and clearances. Our mission is to deliver an HVAC installation that heats and cools efficiently without compromising the building envelope .
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Refrigerated path : short and direct route to the technical column of the accommodation, under black UV sheathing to protect the refrigerated insulation (Armaflex) from rays and freeze/thaw cycles.
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Slope and snow management : the equipment is placed away from prevailing gusts of wind, with a clearance of 30–40 cm under the chassis to allow air circulation and facilitate the evacuation of ice during defrost cycles.
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Maintenance access : positioned near the access hatch, in a safe area, without obstructing drains or roof vents.
Roof support: stability, load distribution and zero perforation
To preserve the membrane, we use a raised aluminum support placed on distribution soles . Here we distinguish:
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Treated wooden rails resting on high-density foam distribution pads : they diffuse the condenser load and protect the TPO/EPDM membrane.
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Adjustable feet with anti-vibration pads : they limit the transmission of vibrations to the structure and allow precise leveling of the device, essential for the flow of condensates.
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No perforation : the mechanical fixing is not anchored to the slab; stability results from load distribution and frame bracing — a solution recommended by most condominium associations.
This system is complemented by a cleared road surface for our technicians, to ensure safe work in both winter and summer.
Condensate and frost management: avoiding ice patches
Wall-mounted heat pumps in heating mode periodically generate frost on the outdoor heat exchanger. We anticipate:
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A clear clearance under the unit so that water flows towards the natural drainage areas of the roof, away from the drains to avoid icicles around the grilles.
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A discreet deflector under the housing (when required) which channels runoff from defrosting.
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A controlled inclination of the chassis (a few millimeters) to promote flow, verified electronically during commissioning.
Electricity and compliance: safety first
On roofs, exposure to the elements requires impeccable execution:
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External disconnection in a waterproof, accessible and visible box.
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Metal conduits and cables rated for outdoor use, compressed joints and sealed edges.
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Checking the currents and adjusting the circuit breaker according to the nameplate; checking the direction of rotation of the fan and the defrost sequence .
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Compliance with RBQ and building engineering requirements; grounding and insulation testing before charging.
Refrigeration: vacuum, charge and fineness of connections
We install new refrigeration lines (annealed copper), insulated and sleeved against UV rays. The key steps:
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Nitrogen brazing (or flared fittings calibrated according to the Midea technical data sheet) with visual inspection and nitrogen pressure test.
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Deep vacuum < 300 microns, resistance test and validation by sensors.
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Opening the circuit and adjusting the additional load if the length exceeds the factory load.
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Control of subcooling and superheating , temperature/pressure readings in cold and hot mode, then acoustic verification (bearing, turbine, parasitic vibrations).
Challenges of this project… and our solutions
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Snow on the ground and meltwater : we planned the intervention during a stable weather window and secured the work area with non-slip mats ; the distribution rails on skids protect the membrane from freezing/thawing punctures.
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Visible route on the roof : the technical ducting groups together the connections (refrigerator + communication + power supply), reduces the visual footprint and simplifies maintenance .
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Old equipment nearby (condenser of a previous brand seen on the roof): disconnection and clean decommissioning , avoiding any interference with the new device.
Measured results: comfort, silence and savings
After commissioning , the readings show:
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In negative temperature heating mode, remarkable blowing stability and short defrost cycles, imperceptible on the housing side.
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In air conditioning mode, a contained exterior noise level (important for the peace and quiet of the neighbors) and fine modulation adapted to the partial loads of summer evenings along the Lachine Canal .
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Reduced electricity consumption compared to the old system, thanks to R-454B and the inverter, with predictable savings over the season.
AirGreen Best Practices for a Rooftop Heat Pump
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Always distribute the load on suitable rails/pads, never directly on the membrane.
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Allow 12–18 inches of clearance under the base for snow and ice.
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Position the rear of the unit away from prevailing winds; limit recirculation near guardrails.
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Protect connections from UV and shocks; inspect collars and seals annually.
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Schedule HVAC maintenance before winter: cleaning the coil, checking the fans, updating the firmware if necessary, and validating the defrost sequence .
Grants and administrative support
Depending on the chosen configuration and performance, the installation may be eligible for energy efficiency grants . Our team assists co-owners in preparing files and validating criteria (power, efficiency, cold climate). Whether you are in Montreal, Laval, Longueuil, on the North Shore or the South Shore , we guide you from the thermal assessment to claiming grants when eligible.
Why entrust your project to AirGreen?
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Specialists in HVAC installation on flat roofs, balconies, backyards and tight spaces.
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Mastery of reference brands , including Midea in R-454B extreme cold.
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Quality procedure : load calculation, route study, documented vacuum draw, test sheets and maintenance booklet given to the client/union.
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Local after-sales service , rapid response and stock of common parts for peak season.
And now, time for your comfort
This Midea wall-mounted heat pump installation in Lachine combines performance, energy efficiency, and roof protection . The result: a comfortable four-season home, a reassured condominium, and a sustainable solution, ready to face our winters.
Are you considering a wall-mounted heat pump on your roof, balcony, or slab? Our team operates throughout Greater Montreal . Contact AirGreen : we analyze your building, recommend the right capacity (BTU) , and deliver a clean, compliant, and sustainable installation .