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

Installing a central system in a house that has never had a single duct

At Mont-Saint-Hilaire, much of the residential housing stock was built without an air-distribution system. Heating with electric baseboard heaters, room by room, thermostat by thermostat. It is simple, quiet, and durable — and completely unable to provide air conditioning, filtration, or air circulation.

The project discussed here falls into this category. A mountainside house, a basement undergoing renovation, no ductwork anywhere, and owners who wanted three things at once: central air conditioning, a lower heating bill, and an end to radiators beneath the windows. At AirGreen, this type of conversion represents a growing share of our work on the South Shore, and it is also the most demanding from a design standpoint — because the real project is not the appliance, but the network that must be designed around it.

The starting point: no furnace to copy

For a conventional replacement, there is an existing appliance whose nameplate can be read. Here, there is nothing. And the most common temptation is to add up the capacity of the installed baseboard heaters and use it to determine the size of the central system.

It is a mistake, and it systematically leads to oversizing. Electric baseboard heaters are installed according to generous construction practices: a 1,400 sq. ft. house often has 12 to 15 kW, even though its actual load at -23 °C is more likely between 8 and 10 kW. Installed capacity is a ceiling, not a measurement.

What we use instead:

• A room-by-room load calculation, based on the actual building envelope: insulation, window area and orientation, airtightness, and heated volume.
• The consumption history in kWh provided by the utility, which gives a direct reading of what the house actually consumed, month by month.
• The design temperature for the Montérégie region, around -23 °C, not the coldest day ever recorded.
• The client's projects: a basement being made habitable, windows to be replaced, insulation to be redone. The load is calculated for the house that will exist, not the one being demolished.

Why the 2-ton GREE UNIX R32

The selected configuration is the smallest in the lineup: indoor unit GUD24AH2/G-D(U), condenser GUD36W2/NhE-D(U), AHRI 217120759 code.

A detail few people check

The four figures printed prominently on the cover of the UNIX R32 documentation—18.0 SEER 2, 12.5 EER 2, 10.0 HSPF 2, and a COP of 3.60—are not lineup-wide values. They correspond exactly, and only, to this 24,000 BTU/h column. The 3-, 4-, and 5-ton models show COPs of 3.20 to 3.40 and EER 2 ratings of 11.7 to 12.0.

In other words, the model installed here is the most efficient in the series. We mention this because the opposite is more common: on many sales sheets, the coverage figures belong to the model the customer will not buy. Our rule is to verify performance using the AHRI code for the exact indoor-outdoor combination, never the coverage page.

The narrowest cabinet in the lineup

At 460 mm wide, this cabinet is nearly 7 inches slimmer than the 4- or 5-ton model. In a basement renovation where every square foot has already been allocated, that difference determines whether the unit fits in an enclosed utility room or encroaches on the family room. The weight follows suit: 61.5 kg versus 90.5 kg for the larger models, which also changes the trip down the stairs on delivery day—and the trip back up in twelve years.

The sizing question, asked honestly

A 2-ton system retains 100% of its heating capacity down to -20°C thanks to Ultra Heat technology and operates steadily down to -30°C. At peak modulation, it reaches 30,000 BTU/h.

Is that sufficient on its own at −25°C in the Richelieu Valley? No, not in this house. And that is precisely the purpose of the built-in electric element in the air handler, which takes over during the few dozen coldest hours of the year. We prefer this approach to the reflex of installing 4 tons: an oversized unit spends the winter modulating poorly, stopping and restarting, and in summer loses the ability to drop to 12,000 BTU/h—which is exactly what is needed to dry the air in a house located a few hundred meters from the river.

Designing the duct network before choosing the route

This is where the project's success is determined. The unit operates at 760 ft³/min against a nominal external static pressure of 125 Pa (0.5 in. w.g.). This figure is not something we observe afterward: it is the budget used to design the network.

The main trunk and its route

In the jobsite photo, the new rectangular trunk runs beneath the joists, made of galvanized sheet metal fabricated and assembled on site, with a second branch turning at an angle toward the other end of the basement and a branch connection in insulated flexible duct. Three decisions were made before the first cut:

1. The routing. The trunk follows the line where the finished ceiling will be lowest anyway—along a load-bearing wall—rather than crossing the middle of the future family room.
2. The gradual reduction. A trunk that maintains the same cross-section along its entire length wastes pressure and unbalances the last outlets. Ours is reduced after each group of branch ducts.
3. The risers to the upper floor. In a house without ductwork, these are what make or break the project. We identify them before selling the system: stacked closets, interior wall cavities, a corner of a wardrobe. A single impossible riser can rule out an entire room.

Lost headroom, calculated in advance

A main trunk and its insulation typically take 8 to 10 inches below the joists. In a 7-foot-6-inch basement, that is not a minor detail—it is the difference between a comfortable finished ceiling and a low corridor. We provide this figure to the client and their renovation contractor before the drywall is ordered. On this project, coordination with the work already underway allowed the ducts to be installed while the structure was still open, with no rework at all.

The way back

This is the most common oversight when converting from baseboard heating. A central system works only if air can return. Bedroom doors closed at night, no return duct upstairs, and the room becomes pressurized while the rest of the house depressurizes. Depending on the configuration, we add transfer grilles, door undercuts, or a dedicated high return. A single central return is acceptable only if the return paths are genuinely unobstructed.

The refrigerant path inside the building

On this project, the refrigerant lines do not run along the exterior wall: they enter the side of the cabinet, form a wide curve, and rise vertically through the structure to the exit point. Three requirements apply to this type of interior routing:

• Continuous, uninterrupted insulation on the suction line. In cooling mode, this line is cold. An uninsulated section inside a wall cavity produces condensation in a place where no one will see it until a stain appears on the ceiling of the floor below.
• Bend radii maintained. A pinched line cannot be repaired; it must be replaced—and it will be inside the wall.
• Controlled lengths. The factory charge covers 7.5 m of piping, and the maximum permitted length is 30 m with a maximum elevation difference of 15 m. Any additional length requires refrigerant to be added, weighed, and recorded.

The entire assembly is sleeved where it passes through the floor, protecting the insulation and allowing future replacement without opening the structure.

Condensate, R32, and the electrical system

The condensate drain was installed with a trap, cleaning plugs, and continuous slope, along with a high-level safety switch that shuts off the unit before the water overflows. In a basement that is going to become habitable space, this is not optional.

All GREE Canada indoor units in this series include a refrigerant leak detection sensor. R32 is a low-global-warming-potential A2L refrigerant; the volume analysis is based on the space served by the duct network, with the unit fully connected.

On the electrical side, the bare cabinet shows an MCA of 4.7 A and an MOP of 15 A. These values are no longer valid once the supplemental heating element is installed: the manufacturer’s documentation states this explicitly, and the MCA and MOP must then be recalculated according to the installation manual, along with the resulting circuit, conductor size, and protection. Conversely, the gradual removal of the baseboards frees up capacity at the panel—a point to document with the master electrician before concluding that the panel is full.

The outdoor unit at the foot of the mountain

The 990 × 960 × 370 mm, 85 kg, 60 dB(A) condenser was positioned with three local realities of Mont-Saint-Hilaire in mind: leaves and pollen from wooded lots and orchards, which can clog a coil in a single season if the unit is placed under a tree; snow sliding off a sloped roof; and meltwater from the defrost cycle, which must drain somewhere other than onto a walkway. Property-line clearances were validated in advance, as several municipalities in the Richelieu Valley regulate noise from outdoor mechanical equipment.

From baseboards to a single thermostat: the conversation you need to have before signing

This is the point we systematically discuss with clients moving away from electric baseboards, because it cannot be resolved after installation.

What you gain, what you lose

With baseboards, each room has its own thermostat. With a single-zone central system, the entire house follows one setpoint, and comfort now depends on balancing the system rather than on a button in every bedroom.

What you gain in return: air conditioning, filtration, heating that costs three times less in mild weather, an end to curtains turning brown, and a much more stable temperature over time—baseboards operate in short cycles with fluctuations the body can perceive.

Our approach: don't remove everything

We rarely recommend removing all the baseboards on the first day. The strategy we applied here:

• Keep the bedroom and basement baseboards as local supplemental heating for at least one full winter.
• Lower their thermostats a few degrees below the central setpoint so they only activate if the room actually falls behind.
• Balance the system according to the measured flow rate, using the balancing dampers installed on each branch—not by randomly closing vents.
• Reassess after one season and remove anything that was never activated.

This approach costs a little more to configure and provides much greater peace of mind. Above all, it avoids the classic situation: baseboards removed in June and an uncomfortable north-facing bedroom in February.

Mistakes to avoid in this type of conversion

1. Choosing the equipment before designing the duct network. The reverse order is the only defensible one: the load, then the duct network, then the equipment that matches the airflow the network can actually deliver.
2. Adding up the baseboard kilowatts to estimate the system size.
3. Running the main trunk through the only area where the client wanted a high finished ceiling.
4. Neglecting the return-air path in the bedrooms.
5. Interrupting the insulation on the suction line inside a wall cavity or floor void.
6. Using uninsulated flexible ductwork in a cold basement, or installing excessive lengths that sag between the joists.
7. Coordinating the installation after the drywall has been installed, turning a clean project into a series of repairs.

Financial assistance and verification

Replacing fully resistance-based heating with an efficient heat pump is exactly the situation targeted by Quebec assistance programs for customers heated with electricity, led by Hydro-Québec's LogisVert program. The amounts, minimum efficiency criteria, and deadlines change from year to year: we verify eligibility using the AHRI code for the installed combination—217120759 here—rather than the model's commercial name, because this is the number listed in the reference directories.

Our experience in the Richelieu Valley

Each conversion has its own dominant constraint. We reused an existing duct network when replacing an electric furnace in Beloeil, installed a complete system in a 42-inch crawl space in Saint-Mathias-sur-Richelieu, built a retrofit around a coil in a cabinet in Saint-Liboire, and installed an outdoor unit on a raised slab that could not be drilled in Sainte-Madeleine. The equipment changes little; the design changes every time.

Our teams serve Mont-Saint-Hilaire, Beloeil, Otterburn Park, McMasterville, Saint-Basile-le-Grand, Chambly, and the entire South Shore, as well as Montreal, Laval, Longueuil, and the North Shore. For a home heated with electric baseboards, the first step is neither a quote nor a model: it is a load calculation and a ductwork layout. Contact us to schedule this visit before your basement is closed in.