Installation of a 2-ton GREE UNIX R32 central heat pump with integrated auxiliary electric heating (electric furnace) in Otterburn Park, RCM of La Vallée-du-Richelieu

An unfinished basement, a chimney still standing, and 100 amps to distribute

On this Otterburn Park job, the equipment was not the challenge. The challenge was the electrical panel.

We installed a 24,000 BTU/h GREE UNIX R32 air handler, connected to a 36,000 BTU/h condenser, with an integrated supplemental electric heating kit installed in the air handler — this is the component most homeowners rightly call the electric furnace in their system. The assembly rests on a custom-built base plenum in an unfinished basement with concrete block walls, next to a water heater and a metal chimney flue left in place by the previous installation.

Three elements in this basement dictated the entire project: the electrical service, the existing ductwork, and the orphaned chimney flue. Here is how we addressed them, using the actual figures.

Otterburn Park: a housing stock that complicates electrical conversions

Otterburn Park is a small residential town in the La Vallée-du-Richelieu RCM, at the foot of Mount Saint-Hilaire, on the banks of the Richelieu River, next to Mont-Saint-Hilaire, McMasterville, and Beloeil. Part of its housing stock is older, with homes built well before central air conditioning became common, and sometimes originally used as seasonal cottages. On the South Shore, this is a profile we encounter often: wooded lots, unfinished basements, original ductwork, and a 100-amp electrical service that was perfectly adequate at a time when the home had neither a heat pump, an EV charger, nor an induction cooktop.

This is where a conversion succeeds or fails. Adding a central heat pump and supplemental electric heating to a home like this is not a refrigeration piping problem: it is a load calculation problem. So we address that before discussing equipment.

The installed system: a 24,000 BTU/h air handler on a 36,000 BTU/h condenser

The selected combination carries AHRI reference number 217120759:

• Indoor air handler: GUD24AH2/G-D(U)
• Outdoor unit: GUD36W2/NhE-D(U)
• Refrigerant: R32, factory charge of 2.9 kg (102.3 oz)
• Power supply: 208–230 V / 60 Hz / 1 phase

Why use a 2-ton cabinet with a 3-ton condenser

This detail goes unnoticed in the catalogs, yet it is the most interesting technical argument for this configuration. In the UNIX R32 series, the 24,000 BTU/h combination is designated “24000 (24/36)”: the indoor cabinet is 2 tons, but the outdoor unit is the 36,000 BTU/h condenser, exactly the same one used for the 3-ton combination.

The result can be seen in the performance ratings. This combination delivers the best EER 2 in the range, at 12.5, and the best COP at 8 °C, at 3.60 — above the 12.0 and 3.20 of the 3-ton version, and well above the 11.7 and 3.40 of the larger models. The reason is simple: a condenser that is never pushed to its limit operates with a heat exchanger generously sized for the load, lower condensing temperatures in cooling mode, and a more comfortable modulation range. The two-stage, two-cylinder compressor with DC Inverter technology therefore spends most of its life at partial load.

In homeowner terms: in Otterburn Park, this system provides about 3.6 units of heat per unit of electricity consumed under reference conditions, compared with exactly 1 to 1 for baseboard heaters or an electric element. That is the entire difference in the bill.

The savings are not visible at the electrical panel

Here is the downside, and we prefer to announce it before signing rather than afterward. Since the outdoor unit of the 2-ton system is the same condenser as the 3-ton system, its electrical requirements are identical: MCA of 27.7 A and MOP of 30 A. Choosing a smaller cabinet therefore frees up no capacity in the panel on the outdoor-unit side.

Many homeowners assume the opposite — “I’ll choose the smaller one; it will require less electricity.” Here, that is not the case. The only component for which sizing actually changes the electrical load is the auxiliary heat.

Integrated electric auxiliary heat: the electric furnace in the same cabinet

Unlike a setup in which the auxiliary heat is a duct heater installed separately in the ductwork, this project uses the electric element kit housed in the GREE cabinet. In the project photo, the upper electrical compartment, with the panel removed, clearly shows the difference: on the left, the heating kit circuit breakers mounted on their bracket, with the two rubber cable grommets for the power wiring; on the right, the control board and control terminal blocks.

Two real advantages of the integrated solution

• Only one appliance to service. One connection, one access point, one panel to remove for servicing. In an unfinished basement where the ductwork is old and sometimes difficult to access, that matters.
• The auxiliary heat is controlled by the cabinet’s control board, along with the manufacturer’s defrost and timing logic, rather than by an interlock assembly put together on site.

Recalculating MCA and MOP, without exception

The GREE technical data sheet includes a note we take seriously: “Optional auxiliary heat. Consult your certified technician to determine the MCA and MOP values required to use an additional electric element.”

In other words, the 4.7 A and 15 A values in the table no longer apply once an element is installed. By way of illustration, with a 10 kW at 240 V element:

• element current: 10,000 W ÷ 240 V ≈ 41.7 A;
• regulatory adjustment at 125%: approximately 52 A;
• adding the blower motor: approximately 57 A, therefore requiring a 60 A protective device and a copper conductor sized accordingly.

Add the 30 A on the outdoor side and you understand why, in a 100 A home in Otterburn Park with an electric range, dryer, and water heater, the conversation starts with a load calculation compliant with Chapter V of the Quebec Construction Code, not with a model choice. Heating and cooling loads are not simultaneous—we use the larger of the two—but the electric auxiliary heat remains, by far, the heaviest load in the project.

That is also why we size the element according to the building’s actual heat loss, never according to the maximum kilowattage offered in the catalog. An oversized element does not heat the house better: it costs more for wiring and circuit breakers, may require a service upgrade, and makes the load calculation harder to get approved.

Staging: where the savings are lost

A misconfigured auxiliary heater undermines the heat pump’s benefits. The selected setting:

• backup heat on the thermostat's second stage, never systematically in parallel with the compressor;
• outdoor-temperature lockout, so the element does not activate at -3 °C simply because the home is calling for heat more quickly than usual;
• controlled use during defrost cycles, to prevent the registers from blowing cool air without operating the element unnecessarily.

There is considerable leeway because the appliance heats down to -30 °C and retains 100% of its heating capacity at -20 °C thanks to the Ultra Heat function. With a winter design temperature of approximately -24 °C in this area of Montérégie, the backup heat becomes a peak-load supplement and a safeguard, not the primary source of heat for the winter.

What we found—and corrected—in the basement

The orphaned chimney

A metal chimney flue is still in place to the right of the appliance, next to the water heater. This is an extremely common situation when a combustion appliance is removed from a basement, and it is a check we never skip.

The rule we follow is this: when an appliance is removed from a chimney, we must determine what remains connected to it. If a natural-draft appliance remains as the sole appliance, the flue becomes oversized for it, heats poorly, drafts poorly, and may backdraft or condense. There are only two options: properly line the flue for the remaining appliance, or properly decommission it if it no longer serves anything. Leaving a partially abandoned flue behind a new appliance merely shifts the problem into the future.

The ductwork of an older furnace

The existing ductwork was reused—which is one of the advantages of the series, designed for retrofit applications—but not without verification. A principle of physics explains why.

At 760 CFM, a heating capacity of 25,000 BTU/h corresponds to a temperature rise of approximately:

25,000 ÷ (1.08 × 760) ≈ 30 °F, or approximately 17 °C

An older combustion furnace typically operated with a 60 to 80 °F temperature rise. The practical consequence is twofold. First, the air at the registers feels less hot to the touch but is blown for longer: this is normal—it is actually the principle behind efficiency—and we explain it to the customer before the first cold night, because this is the first service call this type of conversion generates. Second, a system designed for lower airflow and higher temperature must be measured before it is approved—especially the return air, which is regularly undersized in original installations.

We therefore measure the actual static pressure and compare it with the 125 Pa (0.5 in. w.c.) specified on the data sheet. The plenum and transition joints were sealed with aluminum tape, visible in the photo. A leaking duct system in an unfinished basement heats the basement, not the house.

The base plenum on the concrete slab

The cabinet does not sit directly on the slab: it is mounted on a custom-fabricated base plenum, sealed, which receives the return air and provides uniform support for the unit’s 61.5 kg. Two benefits: no direct vibration transfer to the slab, and clearance from the floor that protects the electronics in the event of water infiltration—a precaution that makes sense in an older home’s basement near the river.

Service valves accessible without removing the cabinet

An engineering detail that makes life easier for everyone: the UNIX R32 series places the service valves and electrical terminals on the outside. In the photo, the green-capped service port and brass flare fitting are directly accessible from the front of the lower panel. In practical terms, checking pressures, verifying the charge, or connecting gauges can be done without opening the coil compartment. Fewer manipulations mean less risk of damaging the insulation or moving a sensor.

The leak detector label

The lower panel bears a bilingual warning specifying the exact location of the refrigerant sensor. It is not decorative. R32 is classified as A2L, meaning it is mildly flammable, and all GREE Canada cabinets include a detection sensor whose effectiveness depends on its position. Repositioning a sensor “to make room” during servicing defeats the unit’s safety strategy. We systematically photograph this area after every service call.

The mistakes we see most often with this type of conversion

1. Install the auxiliary heat before performing the load calculation. Reversing the order can lead to a project halted by an electrician or to a non-compliant installation.
2. Believing that a smaller cabinet reduces the panel load. Here, the condenser still requires 30 A maximum overcurrent protection, regardless of whether you choose 24,000 or 34,000 BTU/h.
3. Do not oversize the electric heating element “to be safe,” only to pay for additional wire, a larger breaker, and sometimes a service upgrade.
4. Do not leave the supplemental heat running in parallel with the compressor without an outdoor-temperature lockout. This is the leading cause of disappointing bills after a conversion.
5. Do not reuse the duct network without measuring it, assuming that what worked with a 70 °F temperature rise will work with 30.
6. Do not ignore the chimney just because it is no longer part of the new system.
7. Do not explain to the customer that the air will feel less hot to the touch. A two-minute explanation during commissioning prevents a worried service call in January.

Rebate eligibility

The installed combination is AHRI-certified under code 217120759, the exact reference required by rebate programs to validate the declared performance. The criteria, amounts, and required documents vary by year and according to the nature of the replacement—the treatment is not the same for a home moving away from a fossil fuel as for a home that is already fully electric. We verify eligibility with the customer before signing, with the technical file in hand, rather than announcing an amount that may not correspond to their situation.

The result in Otterburn Park

The homeowner now has a modulating central heat pump that provides heating and air conditioning for the house with an efficiency of approximately 3.6 to 1 under reference conditions, properly sized and staged electric supplemental heat for winter peaks, a measured and sealed duct network rather than one that was simply reconnected, and a written commissioning report: pressures, temperatures, airflow, static pressure, verified refrigerant charge, and MCA and MOP values recalculated based on the installed component. This report makes all the difference during the first maintenance visit, five years later, when a different person is the one opening the panel.

At AirGreen

We carry out this type of HVAC installation in Otterburn Park, Mont-Saint-Hilaire, Beloeil, McMasterville, and throughout the Richelieu Valley, as well as in Montreal, Laval, Longueuil, on the North Shore, and on the South Shore. Central heat pumps, wall-mounted heat pumps, air conditioners, air exchangers, supplemental electric heating, HVAC maintenance: our teams use the same measurement and documentation process on every job, whether it is a new construction project or a concrete-block basement where the original chimney is still standing. RBQ: 5645-9605-01.