Installation of a GREE FLEXX R32 central heat pump to replace an electric furnace in Rougemont

When the old electric furnace becomes the starting point for a complete central system

At Rougemont, at the foot of the mountain and in the heart of the orchard country, the residential housing stock tells a simple story: homes built between 1970 and 1995, all-electric, heated by a forced-air electric furnace installed in the basement or a mechanical closet, with a galvanized sheet-metal duct system that has aged well. These furnaces do not fail spectacularly. They age, they are expensive to operate from November to April, and one day the homeowner looks at their Hydro-Québec bill and wonders why they are paying for heating at 100% efficiency while their neighbor gets 300%.

That is exactly the mandate we received for this project. At AirGreen, we replaced an end-of-life electric furnace with a GREE FLEXX R32 central system, while retaining electric backup capacity—a Thermolec add-on air heater mounted directly on the plenum. This is not a half measure. It is the most rational configuration available for an all-electric home in Montérégie.

Replacing an electric furnace is not a simple equipment swap

One point we repeat in every quote: removing an electric furnace to replace it with a central heat pump is not simply a matter of disconnecting one unit and bolting another onto the same plenum. The two machines do not behave the same way within the duct system.

An electric furnace produces high-temperature air. It tolerates a restrictive duct system, undersized returns, and high static pressure because it compensates with the heat of the air. A central heat pump does the opposite: it continuously produces a large volume of moderately warm air. If the system cannot allow this volume to pass through, efficiency collapses and the unit operates poorly for longer periods, consuming more than expected.

The 4-ton GUD48AH2/G-D(U) installed here moves 1,200 CFM at a nominal external static pressure of 125 Pa (0.5 in. w.c.). This is the figure around which the rest of the installation is organized.

What we measured before ordering the equipment

Before even confirming the model, we measured the existing system's static pressure with the old furnace running, then calculated the free area of the return air openings. The verdict was unsurprising for a house of this vintage: the main return was adequate, but the transition between the plenum and the unit, installed on site at the time, created an unnecessary restriction.

We rebuilt it. In the job-site photo, the new galvanized sheet-metal transition and custom-built filter cabinet are visible to the left of the unit, with the aluminum tape still freshly applied and the drill on the floor. This transition is not available in the catalog. It is made for that closet and that duct system.

The filter cabinet holds a 20 × 25 in pleated filter, providing approximately 3.5 sq. ft. of surface area. At 1,200 cu. ft./min, this results in an airflow velocity of approximately 345 ft./min—low enough that the filter itself does not become the main restriction as it loads up. A 16 × 20 in filter would have exceeded 650 ft./min and required monthly replacement.

The part few people explain: the air temperature at the registers

Here is the warning we give systematically before signing, because it prevents an unnecessary service call three weeks after commissioning.

An electric furnace delivers air at 50 or 60 °C to the registers. You can feel the heat coming out. A central heat pump in normal operation delivers air between 35 and 43 °C. That is warmer than skin temperature, but cooler than what the homeowner has been used to for twenty years. The body interprets this air as lukewarm, sometimes as cool.

The home reaches and maintains its setpoint. The thermostat is satisfied. But the sensation is different, and if no one has prepared the customer, they conclude that the system is not heating. We prefer to say so in advance, with the numbers, rather than defend it afterward.

The Thermolec air heater: why an electric resistance heater in a high-efficiency system

The question comes up with every all-electric project: if the heat pump operates down to -30 °C according to the FLEXX specification sheet, why add electric resistance heaters?

The answer lies in a distinction that the sales sheet fails to make. Operating at -30 °C and covering the home's heating load at -30 °C are two different things. A heat pump loses capacity as the outdoor temperature drops, while the home demands more. The two curves intersect at one point—the balance point. Above it, the heat pump is sufficient on its own. Below it, something is missing.

What is missing is the Thermolec auxiliary air heater visible on the plenum, with its white cover and circular opening for access to the wiring.

The air heater is not sized by guesswork

The FLEXX sales sheet gives the operating range (-30 to 24 °C in heating mode) but no capacity table based on outdoor temperature. These tables exist — they are in the manufacturer's extended technical documentation, not on the sales sheet. This is the documentation we consult.

The method is as follows:

1. House load calculation at the region's winter design temperature (a house in Rougemont, more continental than Montreal's suburbs, is calculated at a colder temperature than a Plateau plex).
2. Heat pump's declared capacity at that same temperature.
3. The difference is what the air heater must provide — no more.

Oversizing the air heater is a common and costly reflex. An oversized heater bank drives up the home's electrical load calculation, requires a larger conductor, a larger circuit breaker, and sometimes a complete service upgrade that was not necessary.

The electrical arithmetic, done correctly

For a 10 kW at 240 V air heater, arranged in two 5 kW stages:

• 10,000 W ÷ 240 V = 41.7 A
• Continuous load, increased by 125% = 52.1 A
• Protection: 60 A circuit breaker, #6 AWG copper conductor

In this project, the following are also added:

• Outdoor unit GUD60W2/NhE-D(U): MCA 39.9 A, MOCP 45 A
• Indoor unit GUD48AH2/G-D(U): MCA 7.1 A, MOCP 15 A

That is 120 A of connected HVAC load, before even counting the water heater, range, and dryer. On a 100 A service, this will not pass without a proper load calculation; on 200 A, it generally works well. The load calculation under the Quebec Construction Code, Chapter V — Electricity is carried out by the master electrician before the equipment is ordered, not afterward. We have seen too many job sites where the air heater arrives and no one has checked the panel.

The detail that makes the difference between an air heater that works and one that trips

An auxiliary air heater installed downstream of a variable-speed unit presents a problem that conventional furnaces do not.

The FLEXX is an inverter-driven system. In gentle heating mode, its fan can run well below its rated airflow. If the electric heaters engage while the fan is running at low speed, the temperature rise in the duct becomes excessive and the thermal limit switch trips.

The figures, for 10 kW (34,120 BTU/h):

The solution is not to reduce the air handler's capacity. It is to interlock the auxiliary heat call with a high fan speed, so the heating elements can never engage at low speed. This is a commissioning setting, not an accessory.

The air handler also retains its three independent protections: the airflow switch (which prevents the elements from being energized without airflow), the automatic-reset thermal limit, and the manual-reset backup limit. None of the three is optional, and none should be bypassed to “make the system work for now.”

The airflow direction, written by hand on the sheet metal

The air handler is installed in the supply plenum, downstream of the coil. Never in the return. An electric heater installed upstream of the coil heats the air before it reaches the heat pump, which degrades heating performance and makes cooling nonsensical.

In the job-site photos, you can see the “AIR FLOW” arrows drawn directly on the sheet metal with a marker. This is not decorative. In eight years, another technician will open this closet, and this indication will save them thirty seconds of uncertainty and a possible mistake if they need to disassemble a section.

The mechanical closet: where good installations stand out

This system is installed in a finished mechanical closet, on a hardwood floor, within the living area. That changes several parameters.

Condensate management above a finished floor

In air conditioning, the equipment produces water. In an unfinished basement with a floor drain, a condensate leak is an inconvenience. Above a hardwood floor, it is a disaster.

So we treated drainage as a critical item:

• Condensate trap properly sized for the cabinet's negative pressure, with accessible cleanout plugs
• Secondary drain pan beneath the unit—the galvanized base visible at the bottom of the unit
• Float switch in the secondary drain pan, wired to interrupt the 24 V circuit and stop the system before water reaches the floor
• Continuous slope toward the drain, checked with a level over the entire length

Every summer, we get called about water damage caused by improperly drained condensate. In nearly every case, the float switch was missing. It is the least expensive component in the entire installation.

A2L refrigerant in a confined space

The FLEXX uses R32, an A2L-classified refrigerant—slightly flammable. This unit contains 4.6 kg of factory charge, the largest in the range.

The system comes with a factory-installed A2L leak-detection sensor, and the unit's cabinet bears the corresponding safety label, clearly visible in the photo. The mitigation principle is simple: if a leak is detected, the controller starts the fan to disperse the refrigerant through the duct network and prevent any accumulation.

This has a practical consequence that is often overlooked. The reference volume for the safety calculation is not the closet's volume, but that of the space served by the ducts—precisely because dispersion occurs through the fan. This means that the unit's power supply must never be installed on a circuit that someone could switch off “because it isn't used in winter”. Mitigation requires the circuit to remain energized.

Service clearances, determined before construction is complete

The unit measures 24 4/5 × 52 1/16 × 21 1/4 in and weighs 199.5 lb. It occupies most of the closet.

The adjacent storage shelf, loaded with boxes, and a bag of insulation placed on top of the unit are already visible in the photo. That's the reality of every mechanical closet: they become storage spaces. We cannot prevent this, but we can ensure it does not become a problem.

What we protect, in practice:

• Front access to the coil panel and electrical box—the front must remain clear
• Access to the filter cabinet without having to move anything
• The top of the unit, where the power connection runs
• The path for removing the unit when it eventually needs to be replaced

We systematically provide the customer with written instructions: what may be stored, and where. It's more effective than a prohibition sticker that nobody reads.

The side refrigerant connection

The FLEXX's service valves and refrigerant connections are located on the right side of the cabinet, as the photo confirms: the black insulated line runs down along the right wall, and the two connections—3/8-inch liquid and 3/4-inch gas—are accessible from the front without removing a panel.

This detail dictates the unit's orientation in a narrow closet. Placed on the other side, the installation would have been functional, but the first service visit would have been unpleasant.

The factory charge covers 7.5 m (24.6 ft) of piping, the maximum length is 30 m (98.4 ft), and additional refrigerant is calculated at 0.22 oz/ft (20 g/m) for this size. The amount added is weighed on a scale and recorded on the charge label affixed to the outdoor unit.

Technical data for the system installed in Rougemont

The control strategy: make the heat pump work, not the heating elements

A poorly configured central heat pump with electric auxiliary heat can cost more to operate than an electric furnace. The mechanism is simple: if the thermostat calls for the heating elements at the slightest deviation from the setpoint, the home is heated at 100% efficiency by a machine that could do the job at 300%.

What we adjust during commissioning:

• Auxiliary-heat call differential — the heating elements engage only after a real, sustained deviation, not as soon as the temperature is off by one degree
• Outdoor auxiliary-heat lockout — above a specified outdoor temperature, the heating elements are physically disabled
• Compressor lockout in emergency mode only, never during normal operation
• Defrost recovery delay, to temper the supply air during the cycle without unnecessarily heating both floors
• Scheduled recovery — a thermostat that raises the setpoint by 3°C all at once in the morning will call for auxiliary heat every time; a gradual increase lets the heat pump do the work

These settings are not visible in a photo and do not appear on any invoice. Yet they determine the electricity bill for the next ten years.

Eligibility for rebate programs

The installed system carries ENERGY STAR certification and a certified AHRI number (217120761), the two elements that government and Crown corporation programs normally require to validate an application.

We deliberately remain cautious about amounts: eligibility requirements, performance thresholds, and budget envelopes change from year to year, and a conversion from an electric furnace is not treated the same way as a conversion from a fuel-fired system. We verify the file's actual eligibility before signing, using the exact model numbers, and provide the required documentation. A stated performance rating that does not match the outdoor-indoor combination actually installed is the most common reason for rejection, and it is entirely preventable.

Our approach, from Rougemont to Montreal

This Rougemont project resembles a hundred others we complete each year in Montérégie, on the South Shore, in Longueuil, Montreal, Laval, and on the North Shore. Converting an electric furnace to a central heat pump is now one of the most cost-effective projects a Quebec homeowner with an all-electric home can undertake.

However, it requires three things that we refuse to treat as optional: a genuine load calculation, a check of the existing ductwork, and documented commissioning with the auxiliary-electric-heat settings recorded in writing.

At AirGreen, HVAC installation does not end when the equipment starts up. It ends when the customer understands what they have, knows what was adjusted, and has the figures needed to verify it.

The mistakes we see most often with this type of conversion

• Reusing the ductwork without measuring static pressure beforehand
• Installing the air handler in the return rather than the supply
• Sizing the electric auxiliary heat “to be safe” and triggering an unnecessary electrical service upgrade
• Omitting the float switch on the secondary drain pan in a closet above a finished floor
• Leaving the thermostat's auxiliary-heat settings at their defaults, which almost always favor electric resistance heating
• Failing to explain the supply-air temperature to the customer and turning a successful installation into a service call

For an electric furnace replacement, central heat pump installation, or HVAC maintenance project in Rougemont, Montérégie, or Greater Montreal, our team comes to your property, takes measurements, and provides a quote based on actual figures.