Installation of a GREE FLEXX R32 ULTRA dual-energy central heat pump (by Dettson) on a cantilevered platform in Saint-Damase, Les Maskoutains RCM

No ground-level footprint, a natural gas connection to work around, and commissioning completed by work light

In the photo of this project, two details tell the whole story. The first is what you cannot see: there is no ground surface beneath the unit. The second is the yellow line running along the foundation, on the right side of the frame. This is the home's natural gas connection.

These two elements determined the entire project: the mounting method, the choice of equipment combination, and above all, the selected heating configuration. At Saint-Damase, in the Les Maskoutains RCM, we installed a GREE FLEXX R32 ULTRA central heat pump, distributed in Quebec by Dettson, in a dual-fuel configuration with the existing gas furnace.

The Land That Did Not Exist

The strip of land along this wall was completely occupied by an exterior staircase descending to the basement, closed off by a metal hatch. This staircase is an exit and a service access point: it could not be covered, obstructed, or narrowed.

Three options remained, two of which were rejected:

• Move the unit to the back of the building. Rejected: the refrigerant piping run would have become excessive, and the route would have passed beneath a traffic area.
• Build a base above the stairs. Rejected: this would have blocked access.
• Mount the unit on the wall, cantilevered above the void. Selected.

The selected equipment: 48,000 BTU/h and 19 SEER2

This combination choice is not neutral, and we return to it below: in a natural-gas home designed to operate in dual-fuel mode, the 19 TRÉS2 value works hardest for the homeowner, not the heating efficiency in very cold weather.

The cantilevered platform: 241 pounds above the void

Suspending a unit of this mass from the side of a building is anything but ordinary. The difference between a safe installation and a worrying one comes down to four points.

The lever arm

A 241 lb unit whose center of gravity is a certain distance from the wall does not exert a simple vertical load: it exerts a moment, meaning a pullout force on the upper anchors and a compressive force on the lower ones.

The farther the unit is from the wall, the greater this force becomes, without its mass changing by a single gram. This is the purpose of the diagonal braces visible beneath the platform: they transfer part of the load toward the bottom of the wall and reduce pullout at the top.

A platform without diagonal bracing is not an acceptable installation for a unit of this size.

Anchoring into poured concrete

All anchors were installed in the poured concrete foundation. This is the only part of this wall capable of withstanding sustained pullout forces in a building subjected to fifteen years of freeze-thaw cycles and vibrations.

What is unsuitable, regardless of how “solid” the result may look: facing brick, hollow block without through-anchoring, and any nonstructural cladding element.

Every drilled hole was sealed. A foundation drilled without sealant creates a path for water, and a path for water in a foundation always eventually makes itself felt indoors.

Clearance beneath the unit

This was the point that the configuration made mandatory rather than merely desirable: the mounting height had to leave the stairs fully usable, with the hatch open and a person standing underneath.

This constraint produced an appreciable secondary benefit. In winter, defrost water falls freely, and no accumulation of ice on the ground can reach the coil. This is the structural advantage of the suspended installation, and it is why we favor it even when the ground is available but poorly drained.

Vibration isolation

A steel platform bolted to a foundation transmits low-frequency vibrations throughout the structure. Without treatment, the compressor produces a continuous hum that can be heard in the basement and sometimes upstairs.

Anti-vibration pads were installed between the unit’s feet and the platform, and the unit never comes into direct contact with the wall.

The natural gas inlet: required clearances

The yellow line running along the foundation imposes its own rules, and they are not negotiable.

A gas inlet, a meter, and their regulator vents require minimum clearances from ignition sources, electrical equipment, and openings. An electrical disconnect switch, junction box, or outdoor unit improperly positioned in relation to these elements constitutes a code violation, and a violation of this kind is not a matter of paperwork.

The disconnect switch was therefore installed within sight of the unit, at service height, while observing the applicable clearances from the gas inlet. The wall penetration for the refrigerant piping was made with an elbow, continuous insulation, and downward-facing sealing.

This kind of verification takes twenty minutes during the inspection. Done afterward, it takes a day.

Dual energy: what the DT rate really changes

This is the heart of the project, and it is the part that most natural gas homeowners in Montérégie approach with only a rough understanding.

What a dual-energy configuration is

The FLEXX is explicitly designed for this application: the technical specifications indicate compatibility with Dual Fuel configurations, and the unit is controlled by a conventional 24 VAC thermostat, which considerably simplifies integration with an existing gas furnace.

The principle: the heat pump provides heating as long as the outdoor temperature permits, then the gas furnace takes over below a set threshold. The two units never operate at the same time.

How the DT rate works

Hydro-Québec's DT rate is the residential dual-energy rate. Its operation is simple to explain but demanding to follow:

• The switchover occurs at -12 °C or -15 °C, depending on the region. Above the threshold, electricity is billed at the tariff's lower rate; below it, at a significantly higher rate, making the fuel advantageous.
• Hydro-Québec provides an outdoor temperature sensor that automatically controls the switchover.
• A dual-energy meter records consumption at both price levels.
• An automatic transfer switch must handle the transfer between the two sources. Manual switches are possible but discouraged—for an obvious reason: no one gets up at 3 a.m. to switch their house over.

The eligibility requirements include a few surprising points:

• Electricity must be the primary source, with fuel as the backup source.
• The system must be able to provide sufficient heating without simultaneous use of both sources.
• The contract must be eligible for rate D, DP, or DM.
• Electrical installations of 200 A or 400 A and higher are eligible; 320 A installations are not. This is a specific exclusion, often discovered too late.
• The rate is not available in off-grid systems.

The prices for the two tiers were adjusted on April 1, 2026; we verify the rates in effect at the time of each quote rather than citing a figure that will quickly become outdated.

Why the 19 TRÉS2 combination in a gas-heated home

Here is the reasoning we presented to the homeowner, and it runs counter to the usual sales pitch.

In an all-electric configuration, the goal is to maximize heating performance in cold weather because the heat pump must handle the most demanding periods. CPSC2 becomes the determining value.

In a dual-energy configuration, the gas furnace handles precisely the coldest hours. The heat pump operates during the shoulder seasons, in the fall, in the spring, and throughout the cooling season. Its performance at -25 °C has almost no effect on the annual bill because it does not operate at -25 °C.

It is the TRÉS2 that becomes the most cost-effective value—and the selected combination delivers 19 TRÉS2, the best in the FLEXX lineup.

The same outdoor unit, paired with the 54,000 BTU/h indoor unit, would offer a better CPSC2 and a slightly lower TRÉS2. That would be the right choice in an all-electric home. It was not the right choice here.

What dual-energy is not

Three misunderstandings come up constantly:

1. It is not “both at the same time.” The rate specifically requires the opposite, and running both simultaneously eliminates the economic advantage.
2. This is not a choice that can be handled at the thermostat alone. It requires the Hydro-Québec sensor, a dual-energy meter, changeover controls, and an eligible electrical installation.
3. It is not automatically the best choice for everyone. A home with gas heating and a furnace nearing the end of its service life may benefit from considering other scenarios. The calculation is based on the building's actual consumption, not a general rule.

The system's changeover point, distinct from the rate threshold

Important technical nuance: the DT rate threshold (-12 °C or -15 °C) and the heat pump's balance point are two different things.

The balance point is the temperature at which the unit's capacity matches the home's heat loss. The tariff threshold is a contractual rule. Properly aligning them requires knowing the building's actual load and the system's low-temperature capacity, rather than leaving a default value in a thermostat.

We establish this setting during commissioning and validate it through readings in the following weeks, with remote adjustment thanks to the factory-installed Wi-Fi.

Finishing a job at night

The photo was taken by work light, and that deserves a frank explanation rather than staging.

A conversion job is finished when it is finished. A crew that leaves at 5 p.m. with a system only half connected means a house without heating or air conditioning overnight, and sometimes for the weekend.

What does not change just because it is dark:

• Evacuation to below 500 microns using an electronic micron gauge, with a hold test with the valves closed.
• The additional charge weighed on a scale. The unit is precharged for 24.6 ft (7.5 m); beyond that, 0.22 oz per foot (20 g/m) must be added for this model.
• Static pressure and airflow readings on the existing ductwork.
• The photo of the outdoor unit's nameplate, taken while the equipment is accessible — a document required for the financial assistance application and impossible to capture properly once the unit is suspended at height.

What changes: work lighting becomes a safety tool, not an accessory. And the final visual inspection — alignment, clean joints, seal integrity — is repeated in daylight during the follow-up visit.

The tree above the unit

A broadleaf tree directly overhangs the unit. In September and October, the leaves fall into the cabinet and onto the coil.

We warned the owner that fall cleaning would now be part of their routine, just like replacing the indoor filters. A coil covered with a layer of leaves gradually loses capacity without ever triggering an error code — it is the most insidious deterioration we see in HVAC maintenance.

The branches in direct contact with the cabinet were cleared away: a branch that rubs transfers its movement to the structure and wears down the finish.

Six mistakes specific to cantilevered installations and dual-fuel conversions

1. Installing a platform without diagonal bracing for equipment weighing over 200 lb.
2. Anchoring anywhere other than in poured concrete or a verified structural element.
3. Reducing the clearance to an access point or exit to save space.
4. Ignoring the applicable clearances around a gas service entrance and its meter.
5. Choosing the equipment combination based on CPSC2 in a home intended for dual energy.
6. Assuming eligibility for the DT rate without checking the capacity of the electrical service entrance—320 A is not eligible.

Where we work

Our teams serve the Les Maskoutains RCM—Saint-Damase, Saint-Hyacinthe, Saint-Pie, Sainte-Madeleine, La Présentation, Saint-Simon, Saint-Barnabé-Sud—and the entire Montérégie region, as far as Granby, Sorel-Tracy, and Saint-Jean-sur-Richelieu.

Dual-energy conversions represent a significant part of our work on the South Shore—Longueuil, Boucherville, Brossard, Saint-Lambert—as well as in Montreal and Laval, where the natural gas network is widespread in residential neighbourhoods. We also work on the North Shore, from Terrebonne to Saint-Jérôme.

The Saint-Damase homeowner asked us a direct question when we prepared the quote: “Should I disconnect my gas?” Based on the figures for his home, the answer was no. His furnace still had plenty of life left, and dual energy made the most of both systems.

Let's move on to your project

If your home is connected to natural gas, your furnace is still working well, and you want to add central air conditioning while reducing your fuel consumption, dual energy deserves a thorough assessment before any decision to fully convert.

At AirGreen, every HVAC installation project of this type includes an analysis of your actual consumption, load calculations, verification of eligibility for the dual-energy rate, electrical load calculations, and validation of the applicable clearances. Contact us about your central heat pump project in Saint-Damase, in the Les Maskoutains RCM, in Montérégie, on the South Shore, in Montreal, in Laval, in Longueuil, or on the North Shore.