Installation of a GREE UNIX R32 central heat pump in a horizontal configuration with electric backup in Saint-Antoine-sur-Richelieu (La Vallée-du-Richelieu RCM, Montérégie)

When basement height determines the unit's orientation

Most articles about central heat pumps focus on performance, rebates, and tonnage. In the field, the first constraint is often much more prosaic: the distance between the slab and the underside of the joists. In Saint-Antoine-sur-Richelieu, this distance dictated the entire project.

We installed a GREE UNIX R32 air handler horizontally, on wooden supports, beneath a basement ceiling that was too low for the unit to be installed upright. This orientation is not a last-minute compromise: it changes the condensate pan drainage point, the required position of the refrigerant detection sensor, service access, and how the unit is leveled. Here is how we handled it.

Saint-Antoine-sur-Richelieu: a heritage village with basements that were not

Saint-Antoine-sur-Richelieu is part of the Association of the Most Beautiful Villages of Quebec and is located in the La Vallée-du-Richelieu RCM, on the east bank of the river, opposite Saint-Denis. The village core includes old houses, some dating to before Confederation, whose basements were never designed as habitable spaces: limited headroom, full-dimension solid-wood joists, a slab poured later over a dirt floor, and a duct network added in stages over the course of three or four generations of homeowners.

This situation is found just as often in Saint-Denis-sur-Richelieu and Saint-Marc, in Verchères, and in the old neighborhoods of the South Shore and the North Shore. It consistently creates the same problem: the 3-ton air handler is 1,224 mm high, or just over 48 inches, to which a base, a return-air plenum, a supply-air plenum, and the required service clearance above must be added. Upright, the unit does not fit. On its side, it fits—provided the work is done in the right order.

What the survey revealed before the work

Our survey established what the photo shows in part:

• Insufficient clearance for a vertical installation with plenums.
• An existing galvanized sheet-metal duct system, with a black insulated flexible duct dropping diagonally across the space.
• An existing appliance to the left of the selected location, which had to be retained and worked around.
• A sound but uneven concrete slab, with no usable floor drain nearby.
• An exposed wood frame limiting the passage width and prohibiting any appliance more than 24 inches wide at that location.

The 3-ton UNIX R32 air handler is 540 mm wide (21-17/64 in) and 540 mm deep. When laid on its side, it occupies 540 mm in height instead of 1,224 mm. This arithmetic alone made the project feasible without excavating or notching the joists.

The selected equipment: GREE UNIX R32, 3-ton configuration

We chose the air-handler option rather than the cased coil option, and we explain below why the figures support this choice.

Technical specifications for the installed configuration

“36000 (36/36)”: the model name and certified capacity do not say the same thing

The GREE specification sheet identifies this configuration as 36000 (36/36). The certified capacity, however, is 34,000 BTU/h in both cooling and heating. The discrepancy is not a misprint: “36” is a nominal tonnage class—a commercial convention—whereas 34,000 BTU/h is the measured value published under AHRI code 217120760.

The distinction has concrete consequences. A load calculation concluding that 35,000 BTU/h is needed at the design temperature is not covered by a “3-ton” unit in this range, despite its name. In that case, you must move to the 4-ton configuration (48,000 BTU/h certified) or accept that the electric backup heat will operate more often. We prefer to have this conversation before signing rather than on January 1.

Conversely, the 18,000 to 38,000 BTU/h heating modulation range gives the unit genuine latitude: it is not condemned to short-cycle in a home that needs only 15,000 BTU/h in October.

Ventilation cabinet or cased coil: the 3-ton figures

GREE offers two ways to build a central UNIX R32 system. The difference in certified performance is not marginal:

The cased coil still has a legitimate use: it connects to an existing furnace and reduces the cost of a retrofit project, which GREE explicitly identifies as option B for installation flexibility. But it costs 2 points of SEER2 and 1.5 points of HSPF2. In an electrically heated home in the Richelieu Valley, that HSPF2 gap translates into kilowatt-hours every winter, not just on paper. The complete cabinet, with its factory-matched fan and heat exchanger, is the route we recommend when the room's geometry allows it—and here, it did, provided the unit was laid on its side.

A note for contractors consulting the same data sheet: the cased coil table published by GREE contains cells that are clearly incomplete or carried over from one column to another—notably the airflow and dehumidification capacity for the 36,000 column, and identical power entries for the 24,000 and 32,000 BTU/h columns. We systematically validate these values with the manufacturer rather than copying them into a quote.

Laying a ventilation cabinet on its side: what the orientation really changes

This is the heart of the project. A cabinet laid on its side is not an upright cabinet simply placed differently.

The factory label you must not ignore: the A2L sensor relocates

On the face of the cabinet, GREE affixes a bilingual label that reads as follows: if the unit discharges air from the side, as shown in the illustration printed on the label, the refrigerant leak sensor must be placed in the indicated location. In other words, the manufacturer anticipates side-discharge installation and requires a sensor position different from the factory position.

The reason is physical. R32 is denser than air. The detection sensor with which all GREE Canada indoor units come standard is valuable only if it is located where the refrigerant would actually accumulate in the event of a leak. When the cabinet is rotated 90 degrees, the lowest point of the unit is no longer the same: a sensor left in its factory position ends up at the top of the volume, where an R32 leak will never pass.

This is the kind of detail that no commercial brochure mentions and that can only be found in the installation manual and on the label affixed to the unit. An HVAC installation that overlooks this relocation delivers a unit whose A2L safety device is functional on paper but ineffective in practice. We check this point on every horizontal cabinet and record it on the commissioning sheet.

The condensate pan no longer has the same low point

A vertical cabinet drains by gravity toward the bottom of the coil. When laid horizontally, that same coil causes its primary pan to tilt: the drain connection to use is no longer the original one, and the pan must drain toward what has become its actual lowest point.

Two rules govern what follows:

1. Leveling is transverse; slope is longitudinal. The unit must be level along the axis perpendicular to the drainage flow and slightly inclined toward the drain connection. A cabinet that is “more or less level” retains a few millimeters of water in its pan permanently: that is how odors, biological deposits, and, two years later, an overflow are created.
2. The secondary pan is only mandatory in certain situations. When a horizontal unit is suspended above a finished area — a living-room ceiling or an attic space above a bedroom — a secondary drip pan with an independent drain or safety switch is required. On this job, the unit rests on the basement slab: there is no finished space below it, so the secondary pan was not required. We mention this because the opposite — omitting the secondary pan on a suspended unit — is the most costly mistake in the trade.

The condensate trap in horizontal configuration: depth, clearance, and access panels

The cabinet's fan draws air through the coil, placing the condensate pan under negative pressure. Without a sufficiently deep trap, this negative pressure holds the water back instead of letting it drain, and the pan overflows even when the piping is completely clear.

The rule we apply: the trap's water column must comfortably exceed the unit's static pressure. On a cabinet rated at 125 Pa (0.5 in. of water column), a trap with less than 25 mm of water seal is a trap that will not do its job. We systematically aim for twice that.

On this installation, three choices are worth noting:

• A clear-bodied trap, which makes it possible to check at a glance that the water seal is present, without taking anything apart. A trap that has lost its seal in winter—the water evaporates when the unit does not cool for six months—allows basement air into the pan.
• Two cleanouts with caps, placed on either side of the trap, so that future HVAC maintenance can flush and brush the line without cutting the PVC.
• A short route, inside the heated space, never against a foundation wall exposed to the north.

The wooden sleepers are not there for looks

The unit rests on pieces of wood laid on the slab. Three reasons, in order of importance:

1. Adjusting the slope. A basement slab in an older house is never level. The sleepers allow the unit to be set to the desired slope toward the drain, which would be impossible if it were placed flat on the concrete.
2. Breaking contact with the concrete. The fan transmits low-frequency vibrations that the slab spreads throughout the structure. Wood, with a damping material beneath the unit, interrupts this path.
3. Height. Even a modest clearance beneath the unit keeps the sheet metal away from slab moisture and allows the electrical line and drain to pass without being crushed.

We never use untreated wood in direct, prolonged contact with a damp slab, and we never place a 74 kg cabinet on improvised shims: the supports must be continuous beneath the chassis rails, not isolated points under the center of a sheet-metal panel.

Service access: the panel that must be removable ten years from now

In the photo, the side panel has been removed, revealing the fan compartment, coil, and wiring. This is exactly the access a technician will need in five or ten years to replace a motor, clean a coil, or replace a control board.

A cabinet placed against a wall, with its access panel facing the masonry, becomes a unit that must be removed for servicing. We therefore position the unit based on two simultaneous clearances: the service-panel clearance and the filter clearance. In a system that must move 1,000 CFM at 125 Pa, the filter is not an accessory—it is part of the static-pressure budget and must be replaceable without tools.

The refrigerant connection: two insulated lines, not one

The lines visible in the photo are individually insulated along their entire length, including the joints, with sealing tape at the connections. This is a distinction between an air conditioner and a heat pump that many installations miss.

In an air conditioner, only the suction line is cold: it is insulated, while the liquid line remains bare. In a central heat pump, the cycle reverses in heating mode: the larger line becomes a hot-gas line, and the smaller line also operates at temperatures that justify insulation. Leaving the 3/8 in. line bare in a cold basement means losing energy six months of the year and creating condensation during the other six.

The diameters are specified: ø 19 mm (3/4 in.) for the suction line, ø 9.52 mm (3/8 in.) for the liquid line. The standard length is 7.5 m, the maximum length is 30 m, and the maximum elevation difference is 15 m. Beyond the standard length, the charge must be adjusted—and this adjustment must be documented somewhere, not left to the technician's memory.

Electric supplemental heating and the distribution panel

The MCA 5.3 A and MOP 15 A values in the table above apply to the cabinet without a heating element. GREE specifies this in a footnote: as soon as an electric supplemental heater is added, these values change and must be recalculated by a certified technician.

In the village core of Saint-Antoine-sur-Richelieu, as in many older municipalities on the South Shore, a 100 A electrical service remains common. The panel load calculation, performed before the work, determines three things at once: the rating of the supplemental heater that can be installed, whether or not a service upgrade is required, and the rating of the conductors to the outdoor unit (MCA 27.7 A, MOP 30 A).

Backup heat is not a disguised primary heating system. With stable operation advertised down to -30 °C and 100% heating capacity at -20 °C, the heat pump carries the season. The electric element handles peak demand, tempers the supply air during defrost cycles, and serves as a backup. An oversized backup system is expensive to install and even more expensive to operate because a poorly configured thermostat will always call for it too early.

The Errors We Most Often Correct on Horizontally Installed Cabinets

We regularly take over horizontal installations completed by others in Montreal, Laval, Longueuil, and the municipalities of the Richelieu Valley. The same defects keep recurring:

• The A2L detection sensor left in its factory position even though the unit was laid on its side. The device is present, powered, and will never detect an R32 leak.
• The unit installed level in both directions, without a slope toward the drain, leaving a permanent layer of water in the primary pan.
• A trap that is too short, or worse, no trap at all, on a pan placed under negative pressure by the blower.
• No cleanout access on the condensate line, turning the first maintenance visit into plumbing work.
• No secondary drain pan beneath a suspended unit installed above a finished area.
• The uninsulated liquid line, a habit inherited from air-conditioning work.
• The service panel facing a wall, a duct, or a column.
• The original duct network reused without measuring static pressure: a cabinet certified at 125 Pa that must deliver 1,000 CFM through an older home's ductwork that has been expanded three times loses airflow, then capacity, and therefore the certified performance under which it was sold.
• The condensate drain connected without a backflow preventer to a sewer drain, causing odors to return to the basement as soon as the trap dries out.

Subsidies, AHRI Code, and Administrative Pitfalls

A central heat pump with this level of performance is generally eligible for the financial assistance programs offered in Quebec, subject to the criteria in effect at the time of application. The determining factor remains the AHRI reference code for the exact installed combination — here, 217120760 — not the model number of the outdoor unit alone.

This point deserves particular emphasis on this project: the GUD36W2/NhE-D(U) condenser serves both the 2-ton and 3-ton configurations, and it also appears in combinations with a cased coil, whose AHRI codes and performance ratings are different. A rebate application prepared using only the outdoor unit number is incomplete. We provide the complete combination, its AHRI code, and the commissioning sheet, and we recommend validating the current criteria before signing the contract.

What the customer received at the end of the work

• The exact installed combination, with its AHRI code and certified performance ratings.
• Written confirmation of the relocated position of the refrigerant detection sensor, specific to the horizontal installation.
• The measured slope of the unit and the trap's water seal.
• The measured piping length and details of any charge adjustment.
• Commissioning readings: pressures, entering and leaving air temperatures, amperage draw, and measured external static pressure of the duct system.
• The rating of the installed auxiliary heating element and the recalculated MCA and MOP values.
• The procedure for maintaining the filter, trap, and cleanout openings.

AirGreen in the Vallée-du-Richelieu and Greater Montréal

Horizontal installations, low basements, older homes, and duct networks built up over time make up a significant portion of our work in Montérégie. We serve Saint-Antoine-sur-Richelieu and the entire MRC de La Vallée-du-Richelieu, as well as Montréal, Laval, Longueuil, the North Shore, and the South Shore, for both HVAC installation and HVAC maintenance of existing systems.

If you are considering a central heat pump, a wall-mounted air conditioner, a mini-split, or replacing a central system in a home where basement height is an issue, our team assesses the space, ductwork, and electrical capacity before recommending a unit. A properly completed assessment takes an hour. Installing a cabinet in an unsuitable orientation costs much more.