A tight urban construction site, a clean and sustainable HVAC solution: how we optimize under-stair location without compromising on performance
Project background
In a garden-level apartment of a plex in Mercier–Hochelaga-Maisonneuve, the client wanted to modernize its summer and winter comfort, reduce its energy bill, and limit noise for the neighborhood. The available outdoor space was a recess under a concrete staircase, typical of buildings in the area. The goal: to install a Sharp wall-mounted heat pump (ZU1 range, R-32 refrigerant) with the shortest possible cooling path, a clean installation, and compliant air clearances despite the slab above.
Site constraints
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Limited height and concrete ceiling : risk of recirculation of hot air in heating mode and obstruction of the condenser airflow.
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Narrow passage : traffic flow must be maintained for access to the basement and storage areas.
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Uneven masonry wall : Flatness is not perfect, requiring corrections for a level HVAC installation .
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Defrost water management : under the slab, avoid puddles and splashes in winter.
The AirGreen answer
We select a robust galvanized steel wall mount, on anti-vibration brackets , and position the unit at the right height for snow and maintenance. The refrigeration path — insulated ducts visible at the top — remains short (≈ 3 to 5 m) , which limits pressure losses and optimizes seasonal efficiency. The power supply is prepared for a dedicated 240 V circuit, in coordination with the customer's licensed electrician. We leave the required space around the condenser to guarantee frontal airflow and lateral clearances.
Installation details and technical choices
Support and fixing
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Wall brackets with a higher load capacity than the unit, anchored in concrete with mechanical anchors.
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Decoupling silent blocks to reduce vibration transmission to the structure.
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Precise leveling: the front grille must remain perfectly horizontal to promote defrost flow and fan stability.
Refrigerated route
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Set of continuously insulated copper lines (oil return respected), with bending radius controlled by pliers.
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Single drilling as close as possible to the interior evaporator (party wall), in order to reduce lengths and bends.
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Waterproofing of the wall penetration with vapor barrier, air barrier foam and external cap.
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If necessary, we provide aluminum caching (white or anthracite) to protect and standardize the visible exit.
Condensate and defrost management
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In air conditioning mode , the condensates are managed internally (gravity drain prioritized, pump only if the slope is impossible).
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In heating mode , the condenser defrosts periodically: we orient the unit and the floor so that the flow is free, without dripping towards the door or freezing in sheets under the stairs. A dispersion channel can be added if the passage is used intensively.
Clearances and air circulation
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Front face clear across the entire width: no obstacles within 60–90 cm depending on the power.
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Air reflux : the slab above can trap warm air in winter; we move the unit slightly back from the wall and adjust the height to promote lateral evacuation.
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We avoid directing the blower towards closed corners.
Electricity and protection
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Circuit breaker calibrated according to the nameplate, external cable FT4 or equivalent, disconnect in conformity with the local regulations.
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Grounding verified; cable glands and seals to keep out moisture and dust.
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In busy areas, mechanical protection sheath on the electrical downpipe.
Why the Sharp ZU1 (R-32) range for this context
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Four-season performance : a recent R-32 heat pump ensures stable heating at low temperatures and quiet cooling in the summer.
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Energy efficiency : reduced lengths and a clean exchanger under the slab protected from the wind improve the COP in mid-season.
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Controlled noise : the concrete structure and our vibration decoupling reduce sound propagation in the stairwell and towards neighbors.
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Easy maintenance : front access, sufficient side clearances, clear service panels.
The result: consistent comfort, energy savings and a discreet layout, suited to Montreal's urban plexes .
Key steps of our method
1) Technical visit and location validation
We confirm with the client the flow rates, the usual snow depth and the permissible distances. We check the feasibility of an internal gravity drain .
2) Installation of the support and preparation of the drilling
Local straightening of the wall if necessary (stainless steel spacers), sized expansion anchors , tensile test. Marking of the drilling at a 2–3° slope towards the outside.
3) Brazing, vacuum drawing, and testing
Nitrogen brazing, dry nitrogen pressure testing, deep vacuum ≤ 500 microns, stabilization, valve opening, verification of suction/discharge temperatures and currents.
4) Finishes and cleanliness
Stainless steel fixings, protective caps, UV tape on insulation, possibility of adding aluminum capping if the customer prefers perfect aesthetics in this recess.
What the customer gains on a daily basis
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Immediate comfort : rapid temperature rise without overheating the corridor.
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Silence : the modern external turbine and the position between walls reduce noise perception.
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Reduced bill : transferring additional kWh to a high-efficiency heat pump reduces costs compared to electric baseboard heaters.
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Simplified maintenance : seasonal rinsing of the external battery and cleaning of the internal filters maintain efficiency.
Cold Weather Operating Tips in Montreal
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Leave the front of the unit completely clear (no objects, no stacking under the stairs).
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In the event of a storm, clear the base to prevent snow and ice from accumulating under the volute.
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Avoid cutting off the power supply in winter: defrost cycles are automatic.
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Schedule annual HVAC maintenance : pressure/probe check, mild chemical cleaning, electrical tightening, condensate test.
Grants and eligibility (to be validated depending on the configuration)
Recent high-efficiency R-32 wall-mounted heat pumps are generally eligible for assistance depending on performance and the building. In Greater Montreal (Montreal, Laval , Longueuil , North Shore , South Shore ), we assist our clients to verify the criteria (efficiency, nominal temperatures, Energy Star, proof of installation). Our team prepares the documents (photos, serial numbers, detailed invoices) to simplify the filing.
Good practices in confined spaces (under stairs, loggias, courtyards)
To do
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Allow ≥ 30 cm at the back, side and front clearances in accordance with the manual.
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Add snow guards or deflectors if the roof descent will water the unit.
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Fix an anti-icing strip to the ground if the passage is pedestrian and the defrosting water may freeze.
To avoid
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Enclose the unit in an airtight container.
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Hang objects on the brackets or place boards in front of the grid.
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Leave the line insulation exposed to UV without tape/sheathing: it degrades more quickly.
Why choose us for your HVAC installation in Montreal
At AirGreen, we combine site analysis , commissioning rigor, and aesthetic care. Our experience with Montreal plexes (exterior stairs, block walls, tight spaces) allows us to deliver durable, clean, and easily maintained installations . We recommend the right machine—Sharp, Fujitsu, Gree , Midea , and others—based on the housing morphology, heating/cooling objectives, and grant opportunities.
Annual interview: the small gesture that maintains big results
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Cleaning of exchangers (inside/outside)
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Checking the silent blocks and the tightening of the brackets
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Crawl space and defrost drain control
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Remote control update (modes, eco settings, timers)
Regular maintenance means a peaceful winter season, quieter air conditioning in the summer, and performance maintained at its highest.
Conclusion
This Sharp wall-mounted heat pump installation in a recess under the stairs in Mercier–Hochelaga-Maisonneuve illustrates our approach: respecting urban constraints, guaranteeing air clearances, simplifying the refrigeration path , and delivering a reliable, aesthetic and economical solution. For similar projects in Montreal , Laval , Longueuil , on the North Shore or the South Shore , our team implements the same technical requirements — from the first drilling to the last performance test.