Installation of a GREE UNIX R32 central heat pump with an auxiliary electric furnace in Beloeil, Vallée-du-Richelieu

What really happens when an electric furnace is removed from the basement of a bungalow on the South Shore

The mechanical room of this Beloeil home told the whole story before we even opened a panel: an electric furnace nearing the end of its service life, an electric water heater covered with an insulating blanket, a central vacuum attached to the joists, a washer and dryer three feet from the return air, and a galvanized sheet-metal duct network installed with the house. No air conditioning. Every summer, the family brought out two window air conditioners; every winter, the electricity bill climbed without anyone fully understanding why.

At AirGreen, we see this setup almost every week in the La Vallée-du-Richelieu RCM. Replacing an electric furnace with a central heat pump is one of the most cost-effective HVAC projects in Quebec—and one of the most poorly executed when people simply connect a new unit to old ductwork.

The context: an all-electric home and an appliance that could do only one thing

The existing electric furnace did its job: it turned one kilowatt-hour into one kilowatt-hour of heat. Nothing more, nothing less. A 100% efficiency rating, which sounds excellent until you realize that a heat pump delivers three times that amount of heat for the same electricity in mild weather.

What the furnace did not do:

• No cooling. The existing duct network served only six months of the year.
• No modulation. The heating elements ran at full power or not at all, with short cycles and noticeable temperature differences from one room to another.
• No serious filtration. A 1-inch filter in an improvised slot beside a dryer.

The mandate was clear: preserve the duct network if possible, add air conditioning, reduce heating consumption, and maintain electric backup capacity for January nights at -25 °C.

Why we chose the GREE UNIX R32 central system

The GREE UNIX R32 is a central system designed precisely for this type of conversion. It is available in two indoor unit formats: a complete air handler cabinet (the one installed here) or a cased coil installed on top of an existing furnace. Since the electric furnace was headed for scrap, the air handler cabinet was the obvious choice.

The technical overview of the installed system

Selected configuration: 3 tons, indoor unit GUD36AH2/G-D(U) and condenser GUD36W2/NhE-D(U), reference code AHRI 217120760.

Two features weighed heavily in the choice. First, the Ultra Heat series: the unit retains 100% of its heating capacity at -20 °C and operates steadily down to -30 °C. In the Richelieu Valley, where episodes below -25 °C rarely last more than a few days, this means the electric backup remains a backup rather than becoming the main heating mode in January.

Next is the two-stage, twin-cylinder compressor controlled by a DC Inverter. The 18,000–38,000 BTU/h range matters more than the published COP: a home in Beloeil spends most of its heating season between -5 °C and -12 °C, meaning at partial load. A unit capable of dropping to 18,000 BTU/h heats continuously at low speed instead of starting and stopping—that is where comfort and kilowatt-hours are gained.

Why 3 tons rather than 4

It wasn't the floor area that determined the choice, but the duct network. The 3-ton cabinet is designed around 1,000 ft³/min at 125 Pa; the 4-ton model requires 1,200. The existing ducts could not deliver 1,200 ft³/min without exceeding their pressure budget, and an oversized unit that is throttled loses exactly what we came for: the ability to modulate down.

The real challenge in the replacement: ductwork designed for an electric furnace

The good news first: the ductwork of an electric furnace is generally better suited to the needs of a heat pump than that of a gas furnace. The issue lies elsewhere, and it comes down to a formula we apply to every conversion.

The temperature-difference rule

The temperature difference, in °F, is calculated as follows: capacity (BTU/h) ÷ (1.08 × airflow in ft³/min).

• Former 15 kW electric furnace at 1,000 ft³/min: approximately a 26 °C difference, meaning supply air around 46 °C.
• UNIX R32 at 34,000 BTU/h and the same airflow: approximately a 17 °C difference, meaning supply air around 38 °C.
• The same unit at low modulation, at 18,000 BTU/h: approximately 9 °C of temperature difference, meaning supply air around 30 °C.

Remember this last figure; we will return to it below—it explains the only complaint we hear after this type of conversion.

Immediate technical consequence: the furnace tolerated a restrictive duct system because it compensated with a huge temperature rise. The heat pump does not have that margin. Its capacity depends directly on airflow. A system that chokes the unit does more than cause discomfort: it lowers actual efficiency below the certified value.

125 Pa: the number to respect

The cabinet's nominal external static pressure is 125 Pa (0.5 in. w.c.). This is the total available budget for the supply, return, filter, and all accessories. We systematically measure static pressure before and after installation, using a manometer and probes placed on either side of the cabinet.

On this Beloeil job, the corrections were as follows:

1. Complete reconstruction of the supply plenum in new sheet metal, with a gradual transition to the existing main duct rather than an abrupt connection.
2. Enlarging the return air, systematically the weak point of electric furnace installations from the 1980s.
3. Choosing the filter media after measuring, never before. A properly sized deep filter creates less pressure drop than a clogged thin filter, but only if the cabinet is designed for it.
4. Aluminum-tape sealing of every reworked joint, visible on the new surfaces in the photo.

The installation, step by step

The base and base plenum

The cabinet was installed in a vertical configuration on a sheet-metal base plenum set on treated-wood sleepers, serving three purposes: keeping the unit off the water on a basement slab, allowing the condensate drain to slope, and isolating vibrations from the concrete. The UNIX R32 is also compatible with downflow applications, providing flexibility in homes with raised floors.

The external service valves and electrical terminals

This is a design detail we appreciate about this series: the service valves and electrical terminals are external. In the photo, the two copper fittings with green and red caps extend from the bottom right of the cabinet, accessible without removing a panel. In eight years, when a technician needs to take pressure readings or check a connection, they won't have to remove a hatch wedged between the wall and a dryer. Future serviceability is decided on the day of installation.

Condensate in a shared mechanical room

The condensate drain was installed with a trap and cleanout plugs, at a continuous slope, and connected so that it can never discharge into a pan or space not intended for that purpose. We have already handled a water-damage case caused by a condensate drain discharging into a water heater pan: our rule is strict—condensate must go to a floor drain or a dedicated pump with a high-level safety switch, never to an improvised solution.

R32 and the A2L leak detector

All GREE Canada indoor units in this series are equipped with a refrigerant leak detection sensor. R32 is an A2L refrigerant, mildly flammable, with a significantly lower global warming potential than R410A. In a basement, the volume analysis is based on the space served by the duct network, not the volume of the mechanical room—the unit being fully connected to ducts. The 2.9 kg factory charge and line length under 7.5 m allow us to work here without adding or removing refrigerant.

Electricity: the furnace circuit becomes the system's circuit

That is the understated advantage of these conversions. A home heated by an electric furnace already has a high-capacity dedicated circuit at the electrical panel. That circuit is freed up and becomes available for the new system.

The order of magnitude deserves to be stated clearly: a 15 kW electric furnace draws approximately 62 A at peak. The 3-ton UNIX R32 has a rated current of 25.6 A in heating mode, with a 30 A MOP at the outdoor unit. The home's peak demand is transformed as a result.

One warning, however, is stated clearly in the manufacturer's documentation: as soon as an auxiliary electrical element is added to the air handler, the MCA and MOP values must be recalculated. The 5.3 A / 15 A values in the table apply to the bare cabinet. A 10 kW kit adds roughly forty amps on its own and requires its own circuit, conductor size, and overcurrent protection. This calculation must be made according to the installation manual, not the product data sheet.

The outdoor unit

The 990 × 960 × 370 mm, 85 kg condenser was positioned with consideration for defrost runoff, clearance for air circulation, and the path of snow sliding from the roof. At 61 dB(A), the unit remains unobtrusive, but we always check the distances from property lines: several municipalities on the South Shore regulate noise from mechanical equipment, and Beloeil is no exception.

The “less hot” air: the only thing that surprises all our customers, and how we address it

Let's return to the figure mentioned above. At low modulation, the supply air is around 30 °C. Skin temperature is around 33 °C. In other words, a hand placed in front of an air register feels cool air even though the system is heating the house properly.

This is physically normal, and it is the first thing we explain—before installation, never afterward.

What changes in practice

• The cycles are long, sometimes continuous. This is the intended operating mode, not a fault. A heat pump running for eight hours straight at low speed uses less energy than one that starts and stops twenty times.
• The fan runs more often. The sensation of moving air is more noticeable than with a furnace, making the location and orientation of the registers much more critical.
• The temperature becomes stable. The difference between rooms narrows, something the furnace, with its short and aggressive cycles, never achieved.

Set the auxiliary heat so that it remains auxiliary

A poorly configured hybrid system costs more than an old furnace. The settings we program during commissioning:

• Balance point determined according to the home's actual heating load, rather than a thermostat default value.
• Lock out the electric auxiliary heat above this point: as long as the heat pump is sufficient, the elements do not turn on.
• Recovery delay after defrosting, to prevent each defrost cycle from unnecessarily activating the heating element.
• Emergency mode explained to the customer: it is for breakdowns, not cold snaps.
• 24 VAC communication with the wired thermostat, with the UNIX R32 series being compatible with most standard thermostats on the market, as well as with the RS485 protocol.

Mistakes to avoid

1. Reuse the ductwork without measuring static pressure. This is the leading cause of disappointment after a conversion.
2. Program aggressive nighttime temperature setbacks. With a furnace, the morning recovery came at no comfort cost. With a heat pump, a 4 °C setback triggers electric auxiliary heat during recovery and cancels out the overnight savings. Two degrees maximum.
3. Leave the thermostat in emergency mode all winter because “it heats faster.”
4. Close the registers in unoccupied rooms, which increases static pressure and reduces capacity.
5. Placing the dryer facing the return air without an airtight exhaust duct: lint clogs the filter within a few weeks.
6. Forgetting to recalculate MCA and MOP after adding the electric heating element.

Maintenance in a shared mechanical room

A mechanical room that also houses the washer, dryer, water heater, and central vacuum is a dusty environment. Here, we recommend checking the filter every three months rather than every six, keeping the area in front of the access panel clear, and scheduling annual HVAC maintenance that includes measuring pressures, checking the tightness of electrical connections, cleaning the coil, and flushing the condensate drain.

What this changes on the bill

We remain cautious about the figures because they depend on the building envelope, habits, and subscribed rate. What we can say is that replacing fully resistive heating with an Ultra Heat heat pump that maintains its full capacity at -20 °C shifts the vast majority of heating hours to a mode that is three times more efficient.

Two checks are worth making before signing anything: eligibility for incentive programs intended for efficient heat pumps installed to replace electric heating—with Hydro-Québec's LogisVert being the most relevant in this situation—and whether a dynamic rate makes sense, which is only worthwhile if electric backup is actually locked out during winter peaks. Amounts and criteria change over time, so we always validate eligibility using the AHRI number for the exact configuration, here 217120760, rather than the model's commercial name.

Our experience in the Richelieu Valley and Greater Montréal

Every basement comes with its own constraints. We installed this same equipment family in a 42-inch crawl space in Saint-Mathias-sur-Richelieu, on a raised slab that could not be drilled in Sainte-Madeleine, as a retrofit on a coil in a cabinet in Saint-Liboire, and in an adjoining garage ceiling in Saint-Sébastien. The common denominator is never the equipment—it is what we do around it.

Our teams cover Beloeil, McMasterville, Mont-Saint-Hilaire, Otterburn Park, Saint-Basile-le-Grand, Chambly, and the entire South Shore, as well as Montréal, Laval, Longueuil, and the North Shore. For an assessment of your ductwork before replacing an electric furnace, contact us: static pressure is measured in a single visit and determines everything else about the project.