Installation of a MIDEA EVOX G3 electric furnace in a horizontal configuration in an attic in Saint-Philippe, on Montreal’s South Shore

In Saint-Philippe, the main challenge was not only choosing the equipment: we had to successfully complete a full central installation in the attic

This MIDEA EVOX G3 electric furnace installation in Saint-Philippe immediately stands apart from the central installations we carry out in a basement or traditional mechanical room. Here, the indoor unit is placed directly in the attic, in a horizontal position, amid the roof trusses, existing ducts, and blown-in insulation.

The project photograph clearly shows the reality of this type of project. The MIDEA unit is installed along its entire length beneath the roof structure, with visible metal support components, a connection to the duct network on the right side, and several flexible ducts running above and around the unit. The workspace is limited, access is between the structural elements, and much of the attic floor is covered with insulation.

In this context, an HVAC installation cannot be approached as simply replacing one box with another. Even before connecting the equipment, we must consider its orientation, accessibility, airflow path, ductwork, condensate drainage, refrigerant lines, and the possibility of servicing it several years later.

The modular design of the MIDEA EVOX G3 gives us precisely the flexibility needed for this type of project. MIDEA provides six installation orientations, including right-horizontal and left-horizontal configurations, in addition to the vertical and low-boy positions. The manufacturer also states that the modular construction makes it easier to handle the unit in difficult-to-access areas such as attics and basements.

A horizontal configuration particularly well suited to this attic

In a traditional basement installation, a central furnace is often positioned vertically, with the return air on one side and the supply plenum above.

In this Saint-Philippe attic, that approach would not have been logical.

The available height is determined by the roof pitch and the position of the trusses. A vertical installation would have required much more clearance and would have made connecting to the ductwork significantly more complex.

We therefore used the EVOX G3 in horizontal configuration, with the various modules aligned along the same axis.

In the photo, the unit forms a long, compact assembly that can fit beneath the roof framing without unnecessarily encroaching on the available space.

This arrangement offers several practical advantages:

• it reduces the height required for installation;
• it allows the ductwork to follow its natural route;
• it facilitates the use of an attic space that would be difficult to utilize with a conventional upright furnace;
• it allows the technical connections to remain accessible from the service side;
• it limits major modifications to the existing structure.

The modularity of the EVOX G3 really comes into its own when the equipment has to be moved into an attic

A conventional central furnace can be bulky and heavy.

In a basement accessible by a wide staircase, this is already a challenge. In an attic, the issue becomes even more significant.

The MIDEA brochure presents the Block N Lock architecture, which allows the air handler's modules to be separated and reconnected. The manufacturer specifically states that this design facilitates transporting the equipment into difficult spaces such as attics, or entretoits.

In the field, this feature can completely change how we prepare the job site.

Instead of trying to move a very large single-piece cabinet through a restricted access point, we can work with sections that are easier to handle, then reassemble the unit in the designated mechanical space.

For the homeowner, this difference is rarely visible once the installation is complete. For our technicians, however, it can prevent much more invasive work on the building.

Installing in an attic requires a different approach to accessibility

The photo shows a very characteristic environment: exposed structural lumber, blown-in insulation on the floor, flexible ducts, cables, and very few truly clear surfaces.

An appliance installed here may eventually need to be inspected or serviced.

We must therefore avoid positioning the service panels directly against a roof truss or in an orientation that would make access to an important component impossible.

We are particularly considering future access:

• to the electronic control boards;
• to the fan motor;
• to the coil;
• the refrigerant connections;
• the electrical connections;
• the drainage system;
• the panels required for diagnosis.

A proper electric furnace installation in an attic must be planned both for the day of commissioning and for any service work that may be required five or ten years later.

The duct network visible around the unit is an essential part of the system

The photo shows several insulated flexible ducts running through the attic, as well as a sheet-metal connection at the right end of the MIDEA unit.

The central equipment may have excellent performance on paper, but all its energy must then be conveyed through this network.

A significant restriction can increase static pressure and affect:

• the airflow;
• noise level;
• heating capacity;
• cooling capacity;
• motor operation;
• comfort in the most distant rooms.

The EVOX G3 incorporates Computational Constant Airflow 2.0 technology. According to MIDEA, the fan can adjust its output to the network conditions and filtration requirements. The documentation indicates a capacity of up to 1.2 in. of external static pressure under the specified conditions, as well as up to 60 air-volume adjustment levels.

This capability is particularly relevant in a renovation where part of the duct network already exists.

However, this does not mean that we can ignore a poor-quality duct.

If a flexible section is crushed, if a return is too small, or if a transition is unnecessarily restrictive, it is always better to correct the problem than to ask the motor to compensate continuously.

Flexible ducts must be installed carefully

In an attic, flexible ducts are frequently used because they make it possible to work around the framing and reach the various rooms without building a large rigid network throughout.

However, they have their own constraints.

A flexible duct that is too compressed or has several tight bends can create much more resistance than a properly stretched and supported duct.

During our central installations on the South Shore, we therefore pay particular attention to:

• the radius of the bends;
• the length of the runs;
• the mechanical support;
• the diameter;
• the insulation;
• the quality of the connections;
• the airtightness around the collars.

The performance of a new central heat pump depends directly on what is located downstream from the indoor unit outlet.

Why condensate drainage becomes critical in an attic

When a central unit is installed in a basement on a concrete slab, even a small condensate leak can already cause damage.

In an attic, the consequences can be much more serious.

In cooling mode, the indoor coil produces condensation water. This water must be discharged with an appropriate slope and a drainage system designed to remain functional.

We must therefore consider:

• the main condensate discharge;
• the slope of the line;
• cleanout fittings;
• overflow prevention;
• drain accessibility;
• the risks associated with an obstruction.

In the photograph, various technical sections can be seen around the unit, but it does not show the entire drainage strategy clearly enough to detail each component. We therefore prefer not to attribute elements to the image that are not visually confirmed.

This caution is important: a technical article should describe what is actually present, rather than invent details because they are common on other installations.

EVOX G3 performance, cold-climate heating, and technical points to verify before choosing the exact combination

A range of capacities, not a single tonnage

The MIDEA EVOX G3 is available in several capacities.

The technical sheet provided by MIDEA presents combinations ranging from 18,000 to 54,000 BTU/h, including several indoor and outdoor units. Depending on the combination, the range reaches up to 19 SEER2, 12.5 EER2, and 10.8 HSPF2.

The technical table on page 11 details systems rated at 18,000, 24,000, 30,000, 36,000, 48,000, and 54,000 BTU/h, among others. Performance is not identical from one capacity to another.

The photograph of the Saint-Philippe installation does not show a nameplate that is legible enough to determine the exact tonnage of the installed equipment with certainty.

We therefore avoid making it up.

The proper way to identify a central heat pump remains to verify:

1. the exact indoor unit model;
2. the exact outdoor unit model;
3. the certified combination;
4. the AHRI number;
5. heating capacity at temperatures relevant to Quebec.

Down to -30 °C: a particularly important feature on the South Shore

MIDEA documentation presents the EVOX G3 Extreme Heat as a platform capable of continuing to operate in heating mode down to -30 °C.

MIDEA also cites tests on a three-ton system with heating capacity reaching 100% around -25 °C and a COP reaching approximately 1.9 under the specified test conditions.

For a residence in Saint-Philippe, this information is much more relevant than a simple summer cooling capacity.

Our winters require the heat pump to continue producing heat when the temperature drops significantly.

However, two concepts must be distinguished:

• minimum operating temperature;
• capacity actually available at that temperature.

The fact that a heat pump can operate at -30 °C does not automatically mean that it retains its full rated capacity at -30 °C.

That is why we review the data specific to the selected combination before sizing the auxiliary heating.

Auxiliary electric heating must be selected according to the home, not according to the maximum available

The EVOX G3 unit can receive a three-stage auxiliary electric heating kit.

MIDEA indicates capacities of up to 25 kW, with staged management that adjusts the electrical input according to conditions.

For an electric furnace installation in Quebec, the question is not simply: “How many kilowatts can we install?”

We need to determine how many are actually required.

A properly sized auxiliary element must take into account:

• of the home's heat loss;
• of the heat pump's capacity at -8 °C, -15 °C, and lower temperatures;
• of the electrical panel capacity;
• of the conductor ampacity;
• of the airflow;
• of the thermostat strategy.

A modern central heat pump should generally provide a large share of the heating before the electric elements are called on more heavily.

The EVOX G3 uses R-454B refrigerant

The EVOX G3 range uses R-454B, classified as A2L.

MIDEA states that this refrigerant has a global warming potential, or GWP, of 466.

For a homeowner, this does not change how the temperature is selected at the thermostat.

For our technicians, however, this requires methods adapted to A2L equipment, particularly for connection, leak testing, evacuation, refrigerant handling, and commissioning.

In 2026, this expertise becomes particularly important because new central systems are increasingly using this new generation of refrigerants.

Several control options for renovations

The EVOX G3 platform supports different control strategies.

According to MIDEA documentation, the equipment can operate with 485 communication or with 24 V controls, depending on the configuration used. The manufacturer also provides Sub-1 GHz communication with certain EVOX components to reduce the need for communication wiring between the pieces of equipment.

This flexibility can be very useful in an existing home.

In an attic like the one in Saint-Philippe, running new wires to the thermostat can sometimes require much more work than in a new build.

What remains important is to properly configure the heating stages, fan settings, and heat pump logic.

Filtration: the MERV rating alone is not enough

MIDEA also indicates compatibility with 1-, 2-, or 4-inch filters, including MERV 13 in applications specified by the manufacturer.

A more efficient filter can capture more particles, but it can also create more resistance if its surface area or design does not match the required airflow.

We therefore always check the following together:

• the filter size;
• its thickness;
• the airflow;
• the static pressure;
• the replacement frequency.

In a system installed in the attic, where the ducts may already have several changes in direction, it is particularly important not to add an unnecessary restriction to the return air.

What the MIDEA brochure cannot confirm about Québec subsidies

The documentation provided includes several references to U.S. programs, but it does not confirm a specific combination’s eligibility for Hydro-Québec’s LogisVert program.

We therefore must not infer a Québec subsidy solely from the name “MIDEA EVOX G3.”

To confirm a financial incentive for an actual installation in Saint-Philippe, it is normally necessary to have at least:

• the exact indoor model;
• the exact outdoor model;
• the AHRI number of the combination;
• its applicable certification;
• its rated capacity at the temperature used by the program;
• the rules in effect at the time of installation.

The MIDEA brochure can document the general features and performance of the product line, but it cannot confirm the amount of a Québec financial incentive for this specific installation.

Mistakes we want to avoid in a central installation located in the attic

An installation like this reminds us of several practical points.

Installing the equipment before considering future servicing

A horizontal system can easily become inaccessible if its panels are oriented toward a roof truss.

Installing flexible ducts without considering their resistance

A long compressed section or several tight bends can significantly reduce airflow.

Neglecting drainage because the unit is out of sight

A leak in the attic can damage the ceiling long before the homeowner sees the source of the problem.

Choosing the tonnage solely based on the old system

A modern heat pump must be sized according to the residence and the actual heating capacity required.

Unnecessarily oversizing the electric heating

Greater auxiliary capacity does not automatically mean better comfort or greater efficiency.

Forgetting that the attic is a demanding mechanical environment

The location, insulation, ducts, drainage, and service access must all be considered as a whole.

An installation that demonstrates the true value of the MIDEA EVOX G3’s modular design

The most interesting feature of this Saint-Philippe project is ultimately not an efficiency figure.

This is how we were able to install a complete central system in a location where a conventional vertical furnace would have been much less practical.

The photo clearly shows:

• an EVOX G3 installed horizontally in the attic;
• integration between the roof trusses;
• several existing ducts around the system;
• a sheet-metal connection to the main network;
• technical points remaining accessible during installation;
• an environment covered with insulation where every movement and modification must be carefully planned.

This is exactly the type of project where field experience matters just as much as the technical specifications.

At AirGreen, our installations of electric furnaces, central heat pumps, and HVAC systems in Saint-Philippe, Longueuil, Montreal, Laval, on the North Shore and the South Shore are planned around the actual building.

We must determine how to bring the equipment in, how to position it, how to ensure airflow, how to reach the existing network, and how to allow for future maintenance.

In this Saint-Philippe residence, the MIDEA EVOX G3 in a horizontal configuration gave us the flexibility needed to use the attic without imposing a vertical layout that did not suit the building.

The desired result remains the one we pursue with every central installation: a system properly integrated into the network, accessible, adjustable, and capable of providing the expected heating and cooling under the real conditions of Quebec’s climate.