Installation of a GREE UNIX R32 central heat pump with Thermolec electric heating backup in Carignan (MRC de La Vallée-du-Richelieu)

When the mechanical room is also the home's storage area

The Carignan project discussed here stands out neither for its size nor for any spectacular tonnage. It stands out because of a closet. A finished closet, right in the living area, with hardwood flooring, a black-handled door, and metal shelves loaded with boxes from the basement to the ceiling—and in the middle of it all, a 3-ton GREE UNIX R32 central heat pump paired with a Thermolec duct-mounted electric heater for supplemental heat.

This is exactly the kind of installation where the technical data sheet is not enough. A 48-inch-high unit on a basic plenum, in a room where the family will store suitcases and Christmas decorations, requires decisions that do not appear in any catalog: service clearances, noise, condensate above a finished floor, available static pressure, and filter access. We detail each of these decisions here because they are what make a system last twelve years rather than four.

Carignan: all-electric homes, compact houses, and a winter that does not forgive

Carignan is part of the La Vallée-du-Richelieu RCM, between Chambly and Saint-Mathias-sur-Richelieu, on Montreal's South Shore. As in much of Montérégie, natural gas is not the norm in residential areas: homes are heated with electricity, often with baseboard heaters, an aging electric furnace, or a central system with electric heating elements. The winter design temperature used in this area is around -24°C, with lower extremes a few nights each year.

Two practical consequences that we repeat with every estimate on Montreal's South Shore:

• Heating accounts for most of the annual bill, so heating efficiency (HSPF 2, COP) matters more than cooling efficiency.
• The electrical panel is already under load. Adding equipment without performing a load calculation is the best way to turn a beautiful installation into an electrician's problem.

The selected system: GREE UNIX R32, 3 tons, in air-handler cabinet configuration

We installed the following combination, certified under AHRI code 217120760:

• Outdoor unit: GUD36W2/NhE-D(U)
• Indoor air handler cabinet: GUD36AH2/G-D(U)
• Refrigerant: R32, factory charge of 2.9 kg (102.3 oz, approximately 6.4 lb)
• Power supply: 208-230 V / 60 Hz / 1 phase

The figures that matter to a homeowner, not just a technician:

Two characteristics of the UNIX R32 series weighed in the decision. First, the two-stage, twin-cylinder compressor with DC Inverter technology, which modulates instead of operating in an all-or-nothing manner: in Carignan, most heating hours occur between -5 °C and +5 °C, a range in which a modulating unit operates at partial load, quietly, with efficiency higher than its rated value. Second, its low-temperature heating capacity—100% capacity at -20 °C and stable operation down to -30 °C—completely changes the role of the electric backup heat, as we explain below.

The cabinet is also equipped with a refrigerant leak detector, standard on all GREE Canada indoor units. This is not a gimmick: R32 is classified as A2L, slightly flammable, and the sensor is part of the unit's standardized safety strategy.

Why choose a Thermolec duct heater instead of an integrated backup coil

The GREE cabinet accepts an optional electric backup element. We instead selected a Thermolec duct heater, installed in the forced-air duct downstream of the coil. Thermolec is a Montreal-based manufacturer active since 1973, specializing precisely in this type of equipment, and is credited with introducing the electronic airflow sensor in 1998. Three reasons motivated this choice.

A dedicated circuit and a cleaner load calculation

Without an integrated element, the indoor unit remains at MCA 5.3 A / MOP 15 A—a virtually negligible load at the panel. The backup heat, meanwhile, gets its own dedicated circuit, sized according to its power in kW. The result: two clearly separated loads in the load calculation, an identifiable circuit breaker, and much simpler diagnostics five years from now. When everything is stacked in a single cabinet, an element fault and a fan fault look the same to the customer—a system that no longer heats.

The GREE documentation is explicit: the MCA and MOP values must be recalculated whenever an additional electrical element is added. This is not an administrative formality; it determines the wire and circuit breaker ratings.

Proof of airflow: the real key to safety

A duct heater must never be energized without moving air. This is the fundamental principle of the device: the elements dissipate their heat into an airflow, and without that airflow, the temperature rises until the limit switches trip. A correct installation therefore includes:

• an interlock with the cabinet blower, so that air circulation starts before the elements are energized;
• an airflow sensor or switch that cuts power if airflow drops;
• an automatic-reset thermal limit and a backup manual-reset limit.

At 1,000 CFM, we have ample airflow for the installed capacity. But that airflow must be maintained: a clogged filter, a closed damper, or a storage box pressed against a return grille reduces airflow and makes the limit switches work harder. That is why we emphasize filter maintenance so much with customers—here, it is not a matter of comfort, but of safety.

The direction of airflow, marked by hand on the cabinet

On this jobsite, “Air Flow” and two arrows were written in marker on the cabinet, next to the serial number label. It may seem rudimentary. On the contrary, it is one of the best practices in the trade. A duct heater installed backward, or worse, installed on the return side, is a real error that we encounter in existing systems. An arrow visible from the closet door survives every change of ownership and every technician who comes after us.

Installing a complete central system in a finished closet: the constraints we had to resolve

Here, in the order in which they arose on the jobsite, are the challenges specific to this location.

Service clearances versus storage needs

The cabinet measures 21 1/4 in. wide by 21 1/4 in. deep and 48 3/16 in. high, plus the base plenum. In the jobsite photo, the front panels have been removed: the control board occupies the top, the blower the center, and the coil the bottom. Each of these three compartments must be accessible from the front, without removing a shelf or emptying a shelf of boxes.

We therefore set a rule with the client at commissioning and repeat it in writing: the floor area in front of the cabinet, across its entire width, must remain clear. Shelves begin beyond it. This is not contractor rigidity: a technician who has to move a family's belongings before taking out a multimeter bills for that time, or does the job less thoroughly.

Noise in a room opening onto the living area

At 51 dB(A), the cabinet is not loud, but it is not silent either, and it is behind a door, in a finished space, on a hardwood floor. Three measures were applied:

• custom-built, sealed base plenum rather than an improvised vibrating connection;
• gradual transitions to the main trunk to prevent turbulence whistling at 1,000 CFM;
• unit level, evenly supported, with no rigid contact point transmitting vibration to the floor structure.

The major advantage of a modulating system is evident here: most of the time, the fan does not run at maximum speed. An oversized unit that starts and stops at full power can be heard through a closet door at every cycle.

Condensate above a finished floor

In cooling mode, this coil produces water continuously for months. In a concrete basement, a clogged drain makes a puddle. Here, it would cause a warped hardwood floor and, depending on the closet's location, a stained ceiling on the floor below.

Our approach for this type of location: a properly sized trap with a cleaning access, a continuous slope verified with a level, a float safety switch wired to shut the unit down before the water overflows, and a drain routed to a real drainage point — not to a pipe running through a finished room with the hope that gravity will take care of the rest. The float switch costs a fraction of what a floor costs.

Static pressure with a duct heater in the circuit

This is the point most often overlooked. The GREE data sheet specifies a nominal external static pressure of 125 Pa (0.5 in. w.c.) at 1,000 CFM. This allowance must cover everything: the filter, the main duct, elbows, grilles — and the duct heater itself, which adds pressure loss. An electric heating cabinet is not transparent to airflow.

We therefore measure the static pressure before and after installation, and choose the filter media based on the result, not on what is on sale. An overly restrictive filter in this setup does more than reduce airflow: it brings the auxiliary heater closer to its trip threshold.

R32 and the A2L analysis of a fully ducted unit

The closet is small, but the unit is fully connected to a ductwork system. The A2L analysis therefore concerns the volume served by the system, not the volume of the closet, since a leak would be carried into the ductwork by the fan. The 2.9 kg charge is well within the parameters for a single-family home. The integrated detector provides additional protection: if a leak is detected, the unit's sequence uses the fan to disperse the refrigerant rather than allowing it to accumulate.

One detail specific to this location is worth mentioning: this closet contains household products and cardboard. We systematically ask that aerosol containers, solvents, or combustibles not be stored in the immediate vicinity of equipment containing heating elements. This recommendation has nothing to do with R32—it would apply to any heat source.

How the two heat sources share the winter in Carignan

This is the question customers on the South Shore ask most often: “If I still have electric heat, what is the heat pump for?”

The answer lies in the operating range. This system provides heating down to -30 °C and maintains 100% of its capacity at -20 °C. In other words, electric supplemental heat is not the primary heating source for the winter: it is a supplement for peak demand, a way to temper the air during defrost cycles, and a backup in the event of a refrigeration-circuit failure. In Carignan, the vast majority of annual heating hours occur above -15 °C, meaning the heat pump operates in the range where it delivers approximately 3 units of heat per unit of electricity consumed, compared with a 1-to-1 ratio for electric heating elements.

Thermostat settings matter just as much as the equipment. The UNIX R32 series is compatible with standard 24 V wired thermostats and RS485 communication. With a conventional 24 V thermostat, we configure the supplemental heat as the second stage, with a time delay and an outdoor-temperature lockout, so it does not come on simply because the house calls for heat a little faster. Improperly configured supplemental heat can, by itself, cancel out the savings promised by the heat pump—and it is by far the most common cause of disappointing bills after a conversion.

The errors we most often correct on this type of installation

1. Reuse the old ductwork without measuring. A system designed for an electric furnace operating with high supply-air temperatures is not automatically suitable for 1,000 CFM at 0.5 in. w.g.
2. Installing backup heat without proof of airflow. A simple parallel connection to the heating demand, without interlocking it with the blower, is unacceptable.
3. Forgetting to recalculate MCA/MOP when backup heat is added, and leaving in place a wire size selected for the heat pump alone.
4. Sealing the closet airtight, or conversely, installing a return-air grille that draws dust and odors from the storage area into the ductwork.
5. Relying on gravity for condensate drainage, without an accessible trap or safety device.
6. Stacking boxes against the unit as soon as the week after installation. We now leave written instructions on site.

Subsidy eligibility

The UNIX R32 series combinations are AHRI certified — 217120760 for the configuration installed here — and this reference is what subsidy programs require to verify the reported performance. Eligibility criteria, amounts, and documentation requirements change from year to year and differ depending on whether it is a fuel-fired system replacement or a conversion from a fully electric system. We verify eligibility with the customer before signing, based on the AHRI number and technical data sheet, rather than promising an amount that may not apply to their situation.

The result in Carignan

The customer gets quiet, variable-capacity central air conditioning they did not have before, a primary heating system whose output is approximately three times that of their old heating elements, electric backup heat retained for peak demand and emergencies, and a closet that remains usable for storage. The commissioning readings — pressures, temperatures, airflow, static pressure, and verified refrigerant charge — were provided to them in writing. This is the document the next technician will request, and it is worth more than a warranty on paper.

At AirGreen

We perform this type of HVAC installation in Carignan, Chambly, Saint-Mathias-sur-Richelieu, and throughout the Vallée-du-Richelieu, as well as in Montreal, Laval, Longueuil, on the North Shore, and on the South Shore. Central heat pumps, ductless wall-mounted heat pumps, air conditioners, heat recovery ventilators, electric backup heat, HVAC maintenance: our teams follow the same measurement and documentation requirements on every job, whether it involves an open basement or a 21-inch closet. RBQ: 5645-9605-01.