Open panel, visible circuit board, and adapted ductwork: this installation in Sainte-Thérèse shows what a modern central furnace really contains
A modern central electric furnace is very different from the relatively simple units found in many Quebec homes a few decades ago. Our installation of this MIDEA EVOX G3 in Sainte-Thérèse, on the Montreal’s North Shore, provides a particularly interesting view: the photo was taken with the service panel removed, while our technicians were still working on integrating and commissioning the system.
This allows us to see what normally disappears behind the metal panel once the work is complete: control circuit board, terminal blocks, wiring harnesses, low-voltage connections, electrical components, fan section, and cabinet interior layout. Above the unit, a galvanized sheet-metal transition connects the new unit to the existing ductwork. On the right side, the insulated refrigerant line runs to the indoor unit in a space where every connection must be planned to preserve access to the components.
This installation clearly illustrates the difference between simply replacing a unit and carrying out a true central HVAC installation.
Midea’s EVOX G3 line is a family of central ducted Inverter systems, designed in particular to make residential heating upgrades easier. In an existing property in Sainte-Thérèse, this adaptability becomes especially useful: the walls, ductwork, and mechanical space are already in place, and our job is to integrate the new technology cleanly into this infrastructure.
The photo shows the part of the installation that the homeowner almost never sees
Once the front panel is closed, the furnace looks like a relatively understated metal cabinet. Yet behind this façade lies all the system’s operating logic.
In our jobsite photo, the large green circuit board installed in the upper section is immediately visible. It brings together the connections needed to manage various unit components. We can also see several wire harnesses organized inside the cabinet, removable connectors, control connections, and the upper section of the fan compartment.
This architecture is important because an MIDEA EVOX G3 is not merely a box containing electric heating elements.
The indoor unit must manage, among other things:
- the thermostat demand;
- fan operation;
- the different speeds or airflow setpoints;
- interaction with the outdoor heat pump;
- the auxiliary electric heating when required;
- certain communication parameters;
- the system's operating protections.
Midea documentation also provides several control methods. The EVOX can operate with 485 communication control or with a 24 V, including certain configurations using a thermostat from another manufacturer. Midea also provides wireless communication between certain compatible components to reduce the need for additional wiring in some renovations.
For an installation in an existing home, this flexibility can avoid turning a simple central-system upgrade into a major project involving finished walls.
Electric furnace, air handler, and heat pump: three functions that must work together
In everyday language in Quebec, the photographed indoor unit is often called an electric furnace. Technically, it also serves as an air handler for the central heat pump.
When the heat pump operates in heating mode, the energy transferred by the refrigerant reaches the indoor coil. The fan circulates the home's air through the unit and then redistributes this heat through the ducts.
In summer, the process is reversed: the indoor coil cools the air and also helps dehumidify it.
When more heating is needed, auxiliary electric elements can supplement the heat pump.
For the EVOX G3, Midea offers auxiliary heating kits rated at 10 kW, 15 kW, and up to 25 kW, with control that may include multiple stages to adjust electric heating to demand.
In the Sainte-Thérèse photo, we can see the open electrical compartment, but the exact kW output of the installed heating assembly cannot be identified reliably enough for us to state it based on the image alone.
This distinction is important. At AirGreen, we do not infer a furnace's electrical power solely from its external dimensions.
Why the number of kilowatts must be chosen carefully
A 10 kW auxiliary heater and a 25 kW auxiliary heater have very different electrical requirements.
Before determining the power to use, we must consider several parameters:
- the building's heat losses;
- the capacity of the low-temperature heat pump;
- the outdoor design temperature;
- the electrical panel capacity;
- the conductor gauge;
- the required circuit breakers;
- how the thermostat manages the auxiliary heating stages.
Installing the highest available heating element is therefore not automatically advantageous.
The goal is instead to enable the heat pump to efficiently provide a large portion of the heating while retaining enough auxiliary electric heating to maintain comfort when conditions require it.
A particularly useful feature in renovations: multivoltage power supply
Midea also designed the EVOX G3 to adapt to different electrical situations. The manufacturer indicates compatibility 115 V and 208/230 V for the indoor unit according to the configuration and explains that this approach is intended to facilitate certain replacements of existing systems.
However, this versatility should not be interpreted as permission to automatically reuse just any existing electrical circuit.
The power supply for the air handler and that for the electric heating must be checked according to the configuration actually installed. In several replacement projects involving electric furnace in Sainte-Thérèse, Laval, or Montreal, this verification is one of the fundamental steps before the final equipment order.
A duct transition fabricated for the actual building
Above the furnace, the photo shows a metal transition connecting the EVOX G3 to the existing ductwork.
This part of the work might seem secondary compared with the visible electronics in the cabinet. In reality, it directly affects how the system operates.
The air leaving the furnace must pass through the plenum without encountering an abrupt reduction or unnecessarily restrictive geometry. We must also limit leaks at the joints.
A properly constructed duct transition helps to:
- reduce air leaks in the mechanical space;
- limit turbulence;
- control static pressure;
- achieve more even distribution;
- reduce certain aerodynamic noises.
For a central replacement, we therefore work simultaneously on the equipment and how it interacts with the home's ductwork.
The EVOX G3 fan does not operate like an old fixed-speed motor
One of the important technical advantages of this platform is its advanced airflow management.
Midea calls this feature Computational Constant Airflow 2.0. According to the manufacturer's documentation, the system can adapt fan operation to duct-system conditions, including different resistance levels caused by ductwork or filtration. Midea indicates a capacity of up to approximately 1.2 in. of external static pressure, as well as an airflow setting offering up to 60 levels.
For an existing home in Sainte-Thérèse, this feature is particularly relevant.
Residential duct systems are not all identical. Some have long sections, multiple elbows, or more restrictive air returns than others. The unit's ability to adjust fan operation gives us more latitude during commissioning.
That does not mean a poor duct system can be ignored.
Excessive restriction, a crushed duct, a return that is much too small, or a clogged filter must be corrected. Constant airflow technology helps the system adapt; it does not replace proper ductwork design and verification.
EVOX G3 systems available in several capacities
Midea documentation covers various EVOX G3 configurations ranging from approximately 18,000 to 54,000 BTU/h. Depending on the indoor-outdoor combination, the manufacturer indicates performance of up to 19 SEER2, 12.5 EER2, 10.8 HSPF2, and a COP of 2.14 at 5 °F (-15 °C).
The product line includes 18,000, 24,000, 30,000, 36,000, 48,000, and 54,000 BTU/h models.
However, the complete number of the unit installed in Sainte-Thérèse is not legible enough in this photo to reliably assign a precise capacity.
We therefore prefer to present the documented capacities of the product line rather than inventing a tonnage.
To determine the exact performance of an installation, it is necessary to know the precise indoor unit model and the outdoor unit model, then verify the corresponding certified combination.
Heating down to -30 °C: what Midea claims for its Extreme Heat configurations
The EVOX G3 documentation describes certain Extreme Heat configurations capable of continuing to operate down to -30 °CMidea also explains that the compressor technology used is intended to retain more heating capacity when outdoor temperatures become very low.
This characteristic deserves particular attention in an installation with Sainte-Thérèse, where winter heating represents a major part of annual energy consumption.
For us, the important criterion is therefore not solely cooling efficiency.
We also look at:
- the capacity available at low temperatures;
- the COP as the temperature drops;
- the point at which auxiliary heating becomes necessary;
- the way the thermostat manages the transition between the heat pump and electric resistance heating.
A properly selected central heat pump must be evaluated as both a heating appliance and an air conditioner.
From the control board to airflow: the checks that turn installed equipment into a truly functional HVAC system
Access to the electronic compartment must remain possible after installation
The photo clearly shows the space required in front of the unit when adjustments or diagnostics need to be performed.
With the front panel completely removed, our technicians can access the control board, connections, and ventilation section.
This accessibility must be preserved after the work is completed.
An error we sometimes encounter on older installations is placing a conduit, plumbing, structure, or other equipment directly in front of the service panels. The system may operate perfectly at first, but the first repair becomes much more complicated.
When we install a central electric furnace, so we also consider the technician who may eventually need to return to it.
The refrigeration line visible on the right side also requires clean integration
A large insulated line enters from the right side of the unit and connects to the indoor refrigeration system.
Insulating this line is essential. During operation, copper temperatures can differ significantly from the ambient air temperature. Inadequate insulation can cause condensation, thermal losses, or moisture around the line passage.
The routing must also avoid overly tight bends and points that could damage the insulation.
In a central installation, we therefore seek to leave sufficient space between the lines and the cabinet components that will need to be removed during maintenance operationsHVAC maintenance.
R454B and A2L classification
The L’EVOX G3 is part of the new generation of systems using R454B refrigerant.
Midea states that it selected this refrigerant for its product line and assigns it a global warming potential, or GWP, of 466. R454B belongs to the A2L category.
This classification entails adapted installation and service procedures.
For our technicians, this notably concerns handling the refrigeration circuit, refrigerant detection and recovery, and the methods used during service.
The homeowner obviously does not have to manage these technical aspects themselves, but it is important to understand that R454B equipment must be installed and maintained according to the requirements specific to A2L systems.
Filtration: the furnace can also be configured for MERV 13
For the EVOX G3, Midea provides filtration solutions using 1, 2, or 4 inches, with compatibility MERV 13 depending on the configuration.
A higher-performance filter can improve the capture of dust, pollen, and particles, but its selection must be compatible with the ductwork and the desired airflow.
This is one of the reasons why measuring static pressure is so important after modifying the central system.
A homeowner can install an excellent filter and still get poor results if the filter surface is too small for the furnace’s airflow.
Thermostat and smart features: useful only when properly configured
In compatible communicating configurations, Midea also provides functions related to its thermostat and SmartHome app: scheduling, comfort control, monitoring of certain consumption data, as well as diagnostic or update functions.
But our priority during installation remains the system’s mechanical operation.
Before explaining an app’s features, we must make sure that:
- the airflow is correct;
- the system responds properly to commands;
- the auxiliary heating stages are configured;
- the heat pump and indoor unit communicate properly;
- the operating temperatures are consistent;
- the panels and connections are secure.
Smart technology complements a good installation; it cannot compensate for poor commissioning.
LogisVert: the subsidy depends on the complete system, not just the EVOX G3 furnace
For an installation carried out in 2026, the question of financial assistance Hydro-Québec’s LogisVert deserves to be carefully verified.
Since November 26, 2025, Hydro-Québec indicates that heat pumps must be ENERGY STAR certified to be eligible for the applicable measure.
When all program conditions are met, Hydro-Québec currently indicates assistance of $50 per 1,000 BTU/h at -8 °C for an ENERGY STAR heat pump and $120 per 1,000 BTU/h at -8 °C when it is recognized as a cold-climate heat pump. The amount is determined according to the installation date.
In the case of this MIDEA EVOX G3 installation in Sainte-Thérèse, the photo of the indoor unit is not enough to determine the exact subsidy amount.
We must confirm:
- the indoor model number;
- the exact model of the outdoor heat pump;
- the certified combination;
- its rated capacity at -8 °C;
- its ENERGY STAR or ENERGY STAR Cold Climate status;
- the program conditions in effect on the installation date.
It is this complete combination, rather than the EVOX G3 name alone, that makes it possible to properly determine eligibility and the amount.
What we take away from this installation in Sainte-Thérèse
This photo shows a stage that is rarely shown to the homeowner: the furnace open just before all its components become hidden behind the panels.
It shows the true complexity of a modern central system. The circuit board must be configured correctly. The cables must be organized. The fan must meet the needs of the ductwork. The duct transition must provide adequate airflow. The refrigerant line must be protected. The auxiliary heating must be sized according to the home and its electrical supply.
Every element affects the others.
That is why at AirGreen, we approach a MIDEA EVOX G3 electric furnace as a complete HVAC, rather than as a simple replacement of a metal cabinet.
To Sainte-Thérèse, as in our projects in Montréal, Laval, Longueuil, on the North Shore and the South Shore, our job is to adapt the technology to the actual building: its ductwork, electrical panel, heating needs, space constraints, and everyday use.
Once the panels are closed, the homeowner will no longer see this circuit board, the terminal blocks, or most of the settings shown in the photo. They will nevertheless feel their effects every time the system starts quietly, modulates its airflow, and distributes a stable temperature throughout the house.