A six-foot corridor between two concrete walls: what site geometry imposes on a central heat pump
In the photo from this Marieville project, in the Rouville RCM, the unit is installed in a narrow passage between two concrete block walls. The ground is a slab, the walls are stained and moss-covered, and direct sunlight clearly never reaches this spot.
This is the type of location that most quotes cover in a single line: “installation of the outdoor unit at the back of the yard.” Yet, on a site like this, the site's geometry has a greater effect on actual performance than three-tenths of a SEER 2 point.
Two phenomena are triggered as soon as a central heat pump is placed between two closely spaced hard surfaces: air recirculation and sound amplification. We address them before anchoring the support, not after the neighbor's first call.
Air recirculation: the efficiency that disappears without a trace
What happens
The outdoor unit in the UNIX R32 series discharges air through its front, via its two fans. In an open yard, this air moves away and dissipates. In a six-foot corridor, it hits the wall opposite and returns toward the unit.
The consequences are not the same depending on the season:
- In cooling mode, the unit expels hot air. If it draws that air back in, the temperature seen by the outdoor coil rises, condensing pressure increases, capacity drops, and consumption rises. The unit operates, but as if it were 40 °C outside when it is actually 28 °C.
- In heating mode, the opposite happens: the unit expels cold air and draws it back in. The coil sees air that is colder than the actual ambient air, frost buildup accelerates, and defrost cycles multiply just when the home needs heat the most.
In both cases, nothing breaks. There is no error code or unusual noise. The customer simply realizes, two years later, that their bill has not decreased as much as promised.
What we do
- Orient the discharge along the corridor's most open axis, never perpendicular to the nearest wall.
- Measure the manufacturer's clearances with a tape measure, giving priority to the front clearance.
- Raise the unit. In a confined corridor, air stagnates near the ground. A unit mounted higher up operates in a better-renewed layer of air.
- Check what closes off the corridor at both ends. A tarp, temporary shelter, or shed added later turns a ventilated passageway into a closed box.
The noise: 62 dB(A), but measured where
The outdoor unit's technical specifications state a sound pressure level of 62 dB(A). This value is established under standardized conditions, at a given distance, without a nearby reflective surface.
Place the same unit between two parallel concrete walls, and the perceived result changes. Each hard surface reflects sound energy rather than absorbing it, and the reflections add up. The difference amounts to a few decibels—around three to six depending on the configuration—which translates into a clearly perceptible difference to the ear.
What we check at a site like Marieville:
- The distance from nearby openings, particularly bedroom windows, on either side of the corridor.
- Structure-borne transmission. The unit rests on a freestanding support with adjustable feet and controlled tightening: a chassis rigidly bolted to a slab that touches a shared wall transmits compressor vibrations into the neighboring building.
- Municipal noise regulations. They vary from one municipality to another in Montérégie, and they apply at night, when the heat pump is also operating.
One reassuring point about this unit: DC Inverter technology with a two-stage, twin-cylinder compressor allows it to operate at reduced speed for most of the year. A modulating unit remains much quieter than a fixed-speed unit that starts and stops all night.
Permanent shade: an advantage in summer, a constraint in winter
The corridor receives no direct sunlight. This is visible on the walls, where moss has taken hold.
In summer, it is a real advantage. A condenser operating in the shade sees cooler ambient air than a unit exposed to full southern sun on a concrete slab. Cooling efficiency is therefore improved, provided recirculation is controlled.
In winter, this is a constraint. A location that never sees the sun does not dry out. Defrost water — and a 5-ton heat pump produces plenty of it — does not evaporate or melt between cycles. It accumulates as ice beneath the unit.
This is the main reason for the freestanding support with adjustable feet visible in the photo, rather than installing it directly on the slab. The unit is well above the area where ice accumulates, water can fall freely, and the underside remains accessible. The adjustable feet also compensate for the slab's slope and level the unit perfectly — a requirement for defrost water to drain where it is supposed to.
The unit and selected configuration
GREE UNIX R32, 5 tons, with cased coil
The building already had an air handler and a ductwork system in good condition. We therefore chose the cased coil configuration, which retains the existing blower and adds the heat pump coil to the plenum.
- Indoor unit: GCAC60H/NhA — Outdoor unit: GUD60W2/NhE-D(U)
- AHRI code : 216765694
- Cooling capacity : 52,000 BTU/h (15 600 – 57 200)
- Heating capacity : 53,000 BTU/h (16 200 – 59 400)
- SEER 2: 15.2 — EER 2: 9.5 — HSPF 2: 8.5 — COP at 8 °C: 3.10
- Airflow: 1,200 cfm
- Dehumidification capacity: 8.15 L/h, or approximately 17 pints per hour
- Condensate drain: 3/4 in
- Operating temperatures: heating from -30 °C to 24 °C; cooling from -15 °C to 54 °C
- R32 refrigerant, 4.6 kg charge — lines: 3/4 in suction, 3/8 in liquid
- Piping: standard length 24.6 ft, maximum 98.4 ft, maximum elevation 49.2 ft
- Electrical: 208-230 V / 60 Hz / single-phase — outdoor MCA 39.9 A, MOP 45 A
- Coil: 24 1/2 x 28 1/2 x 21 1/4 in, 110 lb — Outdoor unit: 35 25/64 x 49 19/32 x 13 25/64 in, 241.4 lb
- Integrated refrigerant leak detector, compatible with 24 VAC thermostat and RS485
- Ultra Heat: 100% heating capacity at -20 °C, stable operation at -30 °C
The most interesting figure on the specification sheet: 15,600 BTU
On a unit with a nominal capacity of 52,000 BTU/h, the 15,600 BTU/h modulation floor is what truly distinguishes this configuration.
That is less than one-third of the nominal capacity. In practical terms, the unit can run continuously at very low output on mild days in May and September—exactly the periods when a fixed-speed system would simply start and stop without ever dehumidifying.
In a shaded corridor where moisture does not dissipate naturally, the ability to run for long periods at low output matters more than peak efficiency.
Condensate, not to be underestimated
A coil added to an existing unit creates water production where there had never been any: up to 17 pints per hour at peak, discharged through a 3/4-inch drain.
Our requirements: a properly sized and primed trap at commissioning, a safety pan with a float switch when the coil is above a finished space, and accessible cleanout plugs, shown to the customer. This is the most common cause of water damage after adding a coil.
A2L refrigerant
R32 is classified as A2L, mildly flammable. All GREE Canada indoor units—from cased coils to air handler cabinets—are equipped with a refrigerant leak detector. We verify its position and test the shutdown logic during commissioning.
Mistakes to avoid on a confined site
- Treat a corridor like an open yard. The manufacturer's clearances are a minimum, not a target.
- Point the discharge toward the nearest wall because it is more convenient for the piping.
- Place the unit directly on the slab in a location that never dries out.
- Ignore nearby windows and municipal noise regulations.
- Close off the corridor afterward with a shelter, tarp, or shed. What was ventilated will no longer be.
- Forget about service access. A technician must be able to open the side panel and maneuver a cylinder through this passage in February.
Rebates
The Chauffez vert program ended on March 31, 2026. Hydro-Québec's LogisVert program remains the reference assistance program for a central heat pump: eligibility is based on the exact indoor/outdoor combination installed and its AHRI code — here, 216765694 —, on a contractor holding an RBQ licence and registered with the program, and on an application submitted within the prescribed period following invoicing. We validate the combination before signing, never afterward.
Maintenance in a narrow passage
Two points are added to the annual HVAC maintenance on a site like this: clearing the corridor, which has a strong tendency to fill with stored materials over the seasons, and inspecting the coil, which collects dust and leaves trapped between the two walls. Everything else — pressures, superheat, subcooling, airflow, tightening, indoor filters, and the condition of the support — remains part of the usual program.
Why homeowners in the Rouville RCM call us
At AirGreen, we install central heat pumps, wall-mounted heat pumps, mini split systems, air conditioners, and air exchangers in Montreal, Laval, Longueuil, on the North Shore, on the South Shore, and in the municipalities of the Richelieu Valley — Marieville, Richelieu, Chambly, Rougemont, Sainte-Angèle-de-Monnoir, and Saint-Mathias-sur-Richelieu.
A difficult location does not make an installation impossible. It makes preliminary work essential: measuring clearances, directing the discharge, choosing the right support, and warning the customer about what they must not add around their unit in the years to come.
If you need to install a central heat pump in a narrow yard, a shared driveway, or a service shaft, call us. We travel to your location, take measurements, calculate the load, and provide you with a clear proposal including actual performance ratings, the AHRI code, and eligibility for rebates already validated.
AirGreen — Air Conditioning & Heating. RBQ 5645-9605-01. (514) 316-2973