A 30-inch mechanical room, an electric furnace nearing the end of its service life, and a home that had never had central air conditioning
The homeowner wrote to us in February, after an electricity bill had exceeded the psychological threshold of $700 for a two-month billing cycle. His Saint-Paul-d'Abbotsford home, a house built in the early 1990s with approximately 1,750 square feet spread over two levels, was heated by an original electric furnace connected to a galvanized sheet-metal ductwork system that was still in good condition. The unit was still working. That is precisely what made the decision difficult: replacing something that works requires a better reason than a breakdown.
The reason in this case came down to one sentence: an electric furnace converts one kilowatt-hour into one kilowatt-hour of heat, period. A central heat pump delivers three or four for the same kilowatt-hour consumed during most of Quebec's heating season. At AirGreen, we therefore proposed a complete conversion to a GREE FLEXX R32 system, distributed in Quebec by Dettson, while keeping the electric components as backup. Here's how the project unfolded, what caused complications, and what we are taking away for future replacements of the same type on the South Shore, in Montérégie, and in the greater Montreal area.
The context: a 100% electric home with a sound ductwork system
The preliminary inspection is the step that too many contractors skip. We spent nearly two hours on it.
What we found:
- Existing ductwork in good condition, an insulated supply plenum, and a generously sized main return—favorable conditions, which is not the norm.
- Cramped mechanical room: a service cabinet with approximately 30 inches of usable width, wedged between a drywall wall and the return air cabinet, with a hinged door that limited entry clearance.
- A White-Rodgers Comfort Plus HPT2700 humidifier mounted on the plenum, still operational, with its humidistat installed on the duct.
- A White-Rodgers electronic air filter integrated into the return air cabinet, beneath the plenum.
- No floor drain in the immediate vicinity of the future indoor unit location.
- An electrical panel with available capacity, but not unlimited capacity.
Each of these points influenced the equipment selection. The room's width, in particular, immediately ruled out several competing air handlers whose cabinets exceed 24 inches.
Why We Selected the GREE FLEXX R32
The FLEXX R32 is a horizontal-airflow (side-discharge) central system, available from 2 to 5 tons, designed for both existing duct networks and new construction. Three features weighed heavily in the balance for this specific project.
1. Heating range down to -30 °C
This is the most important figure for Saint-Paul-d'Abbotsford, where January nights regularly hover around -25 °C. The FLEXX R32 technical specifications state a heating range of -30 °C to 24 °C and a cooling range of -15 °C to 54 °C. In practice, the compressor continues producing heat through nearly the entire winter, delaying the use of supplemental electric heating elements rather than calling on them at -12 °C, as previous generations of central systems did.
2. Rated efficiencies
For the selected model—the GUD36AH2/G-D(U) indoor unit paired with the GUD36W2/NhE-D(U) outdoor unit, with a nominal capacity of 34,000 BTU/h in cooling and 34,000 BTU/h in heating—the specification sheet indicates:
- 18 SEER2 (SEER2)
- 10 CPSC2 (HSPF2)
- 12 EER2 (EER2)
- COP of 3.2
- AHRI Number 217120760
- ENERGY STAR Certification
The AHRI number is not an administrative detail. It is what validates the indoor-outdoor combination with rebate programs. An uncertified pairing, even if it works mechanically, makes the rebate application ineligible.
3. R32 Refrigerant and the Leak Detection Sensor
The FLEXX R32 uses R32, an A2L-class refrigerant with a global warming potential approximately three times lower than that of the R410A it replaces. The factory charge for this model is 2.9 lb (102.3 oz), with a precharge covering 24.6 feet (7.5 m) of piping and an additional 0.32 oz per extra foot. An A2L leak detection sensor is included from the factory—something we routinely check during commissioning, because an improperly positioned or connected sensor causes nuisance lockouts that are then incorrectly attributed to an equipment defect.
Let's add three features that make the owner's life easier: a 24 VAC supply compatible with a conventional thermostat, factory-installed Wi-Fi, and a standard 10-year warranty, extendable by an additional 2 years when the unit is registered with proof of installation.
The installation: what actually required work
Getting a 74 kg enclosure into a 30-inch cabinet
The GUD36AH2 indoor unit measures 21 1/4 × 48 1/5 × 21 1/4 inches (540 × 1224 × 540 mm) and weighs 163 lb (74 kg) net. On paper, it fit. In reality, the side clearance for maneuvering the unit was no more than three inches on each side.
We temporarily removed the room door, placed the enclosure on sliding skids, and then had two technicians set it upright once it was in position. The unit rests on a raised base with a sound-isolation pad, an inexpensive precaution that prevents fan vibrations from transferring into the floor structure—a common defect in quickly executed replacements.
The electrical supply and fused disconnect
This is where the distinction between a “heat pump” and an “electric furnace” becomes meaningful. The FLEXX indoor unit consumes very little on its own: MCA of 5.3 A, MOCP of 15 A for the blower and controls section. The electric heating elements, however, require their own power supply.
We installed a factory-installed electric heat kit on the unit, protected by a front-mounted fused disconnect split across two circuits (60 A and 30 A). This disconnect, visible on top of the enclosure, allows the power to the heating elements to be cut without touching the main panel—a real time-saver during servicing and a safety requirement we apply without exception.
The outdoor unit has an MCA of 27.7 A and an MOCP of 30 A, which allowed us to power it on a dedicated 30 A circuit without major work at the panel.
The refrigerant line
The distance between the mechanical room and the selected outdoor-unit location was approximately 22 feet, below the 24.6-foot factory-charge threshold—so no refrigerant addition was required. The FLEXX R32 allows up to 98.4 feet (30 m) of piping and 49.2 feet (15 m) of elevation difference between the two units, leaving comfortable leeway for more challenging configurations.
The selected diameters are those specified: 3/8 in. for the liquid line, 3/4 in. for the gas line, insulated along their entire length, including inside the mechanical room. We performed an evacuation below 500 microns with a standing vacuum test, a non-negotiable procedure on an A2L system.
Condensate, with no nearby floor drain
No drain nearby: we installed a PVC drainage system with a compliant P-trap, two accessible cleanout plugs, and a continuous slope toward the existing drain point. The red plugs visible at the base of the unit are not decorative—they allow the homeowner or technician to flush the line during annual maintenance. A clogged condensate drain remains one of the most common causes of water damage in basements, and one of the easiest to prevent.
Keeping the humidifier and electronic air cleaner
The Comfort Plus HPT2700 and electronic air cleaner were retained, cleaned, and rewired to the appropriate terminals on the new controller. Many contractors simply disconnect them during a replacement because they do not want to deal with the interface. The homeowner notices six months later, in the middle of a dry winter.
One technical point is worth emphasizing: with a central heat pump, the supply air is more moderate in temperature and the fan runs longer at low speed than with an electric furnace. The humidistat must be readjusted accordingly; otherwise, the humidifier will activate too often. We recalibrated it during commissioning.
The actual schedule
- Day 1, morning: removal of the old electric furnace, recovery of the wiring, and preparation of the base.
- Day 1, afternoon: positioning of the indoor unit, connection to the supply plenum and return-air cabinet, and sealing of the transitions.
- Day 2, morning: installation of the outdoor unit on its base, refrigerant piping, control wiring, and evacuation.
- Day 2, afternoon: commissioning, thermostat configuration, testing of auxiliary heating elements, verification of the A2L sensor, humidistat adjustment, and customer training.
Two business days, without a prolonged interruption of heating.
The mistakes we see most often—and what this project confirmed
Five pitfalls to avoid when converting an electric furnace
- Oversizing by default. Replacing a 20 kW electric furnace with a 5-ton heat pump “to be safe” results in a unit that short-cycles, dehumidifies poorly in summer, and wears out prematurely. Sizing must be based on a load calculation, not on the capacity of the old unit.
- Neglecting the ductwork. A central heat pump requires sustained, continuous airflow. An undersized return, tolerable with an electric furnace, becomes a source of noise, reduced efficiency, and coil freeze-up.
- Forgetting to lock out the auxiliary heating elements. If the thermostat activates the electric elements at the same time as the compressor without load-shedding logic, the promised savings disappear. This is the main cause of the disappointments reported after installation.
- Underestimating drainage. See above. A missing or improperly oriented trap on a negative-pressure fan unit causes overflow during the very first heat wave.
- Installing without the AHRI number for the exact combination. The rebate application will be refused, and correcting it afterward is rarely possible.
Rebates: what this type of project may qualify for
In 2026, this type of conversion may be eligible for Hydro-Québec's LogisVert program, which provides an amount based on each 1,000 BTU/h increment for approved ENERGY STAR central air-source systems, as well as for the Rénoclimat program's energy assessment component.
The eligibility requirements are strict: an existing home served by Hydro-Québec, ENERGY STAR-certified equipment, a valid AHRI number that exactly matches the installed combination, installation by an RBQ-licensed contractor registered with the program, and submission of the application within the prescribed period following the billing date. Since amounts and terms are revised periodically, we systematically verify eligibility before signing the contract rather than afterward. We should also clarify that a home already heated with electricity is not eligible for the Chauffez vert program, which is intended to replace oil- or propane-fired systems.
Maintenance to plan
- Filter: check every three months; clean the electronic filter cells at the same frequency.
- Outdoor coil: annual rinsing, with snow and ice cleared in winter while keeping the area around the unit unobstructed.
- Condensate drain: annual flushing through the cleaning ports.
- A2L sensor: functional check at every maintenance visit.
- Pressure and overheating: annual inspection by a qualified technician.
Our experience with comparable projects
This configuration—replacing an electric furnace with a central FLEXX system while retaining the backup heating elements—accounts for a growing share of our projects. We have completed it in bungalows in Longueuil and Saint-Hubert, cottages in Laval and Blainville on the North Shore, townhouses in Montreal where the mechanical room is reduced to a closet, and several municipalities in Montérégie, including Granby, Saint-Hyacinthe, Marieville, and Saint-Paul-d'Abbotsford.
The constraints vary from one area to another: tighter regulatory clearances in urban Montreal, longer piping distances in country homes, and electrical panel capacity that is often limiting in buildings from the 1970s. What does not change is the method: load calculation, ductwork inspection, AHRI-certified matching, and documented commissioning.
The result
The homeowner now has a single system that heats in winter, cools in summer, and humidifies during the cold season, controlled by one thermostat and accessible from their phone. The central air conditioning, which had been absent since the house was built, was added without installing new ductwork or carrying out finishing work.
At AirGreen, we design, install, and maintain HVAC systems in Montreal, Laval, Longueuil, the North Shore, the South Shore, and Montérégie. For an assessment of your electric furnace replacement or the installation of a GREE FLEXX R32 central heat pump, our team comes to your property, takes measurements, performs the calculations, and provides you with a proposal based on your actual ductwork—not a generic model.