Installation of a MIDEA EVOX G3 electric furnace in Saint-Théodore-d’Acton, in Montérégie

Replacing a central system without rebuilding the entire mechanical room: a project where the existing ductwork dictated the installation

In Saint-Théodore-d’Acton, in the Montérégie region, we completed an installation of a MIDEA EVOX G3 electric furnace that clearly illustrates the challenges encountered when a modern central system must be installed in an existing home. Here, we did not have a new mechanical room designed around the equipment. We had to work with the existing structure, the large existing galvanized ducts, the available floor space, and a water heater located immediately beside the new unit.

The site photo immediately helps explain the logic behind our work. The MIDEA EVOX G3 is installed vertically, directly beneath the existing air-distribution ductwork. Above it, several galvanized sheet-metal duct sections change size and direction before connecting to the different branches throughout the house. On the right, a Giant water heater occupies a significant portion of the mechanical room. On the left, the framing remains open, allowing us to see the reality of an existing building rather than a demonstration installation carried out in an empty space.

That is precisely what makes this project interesting: the new furnace had to fit cleanly within these constraints without compromising airflow, service access, duct airtightness, or the ability to maintain the other equipment in the room.

A sheet-metal transition specially fabricated for this installation

At the base of the EVOX G3, we can see a new galvanized sheet-metal section fabricated to adapt the furnace to the existing ductwork.

A handwritten annotation, “21 1/4 × 20”, is still visible on the unit when the photo is taken. This is a typical detail of a real HVAC installation: before fabrication and final assembly, our technicians take actual measurements on site so the new equipment fits into the building instead of trying to force a standard connection that does not match.

This sheet-metal work plays a much more important role than its appearance might suggest.

When a new electric furnace does not have exactly the same width or depth as the old unit, a poorly designed transition can cause:

• a sudden reduction in the passage area;
• turbulence;
• an increase in static pressure;
• more noise in the ducts;
• insufficient airflow in certain rooms;
• an additional load on the blower motor.

Our objective is therefore to mechanically connect the unit while maintaining a coherent airflow path.

The old ducts remain in place, but they must be examined as an integral part of the new system

One of the advantages of a well-planned central replacement is that it is not always necessary to redo the entire duct network.

For this installation in Saint-Théodore-d’Acton, we were able to work with much of the existing network. The photo shows, in particular, a substantial main duct above the unit, a vertical transition, and a rounded section connected on the side.

However, “keeping the ducts” does not simply mean connecting the new unit to what was already there.

We must determine whether the network can carry the airflow required by the new installation. This involves considering:

• the dimensions of the main duct;
• the reductions in cross-sectional area;
• the elbows;
• the branches;
• the air returns;
• the filtration;
• the total static pressure;
• the airflow requirements corresponding to the selected capacity.

A central heat pump with Inverter technology can modulate its capacity, but it still needs an air-distribution network that allows it to breathe properly.

An EVOX G3 design particularly well suited to replacement projects

MIDEA developed the EVOX G3 with particular attention to renovations and the replacement of existing equipment.

The manufacturer indicates cabinet widths comparable to those of many traditional furnaces, ranging from approximately 14.5 to 21.5 inches depending on capacity, as well as a design capable of recognizing different power supplies, including 115 V and 208/230 V depending on the configuration.

In a mechanical room like the one in Saint-Théodore-d’Acton, this type of design can avoid much more extensive modifications.

The water heater is already in place. The building structure is fixed. The main ducts run overhead. Simply moving all these elements to accommodate a new unit would rarely be desirable.

Rather, we are looking for equipment that can be integrated intelligently into the existing configuration.

The fasteners visible in the center of the unit reveal the EVOX G3’s modular design

The photo clearly shows several mechanical fasteners on the front of the MIDEA unit. They are related to the platform’s modular architecture.

MIDEA calls this design Block N Lock. The documentation presents several installation orientations: upflow, downflow, right horizontal, left horizontal, and certain “low-boy” configurations. The manufacturer also highlights the possibility of handling the sections separately to facilitate installation in basements, attics, and other difficult-to-access spaces.

In this case, we chose a vertical configuration that fits perfectly with the ductwork layout.

Nevertheless, the benefits of this modularity remain important during installation, particularly for transporting the unit up stairs or through smaller openings.

The proximity of the water heater is not a minor detail

A Giant water heater can be seen on the right side of the photo.

When several mechanical systems share the same room, we cannot consider each appliance independently.

We need to think about future accessibility.

On the day of installation, the space may seem sufficient. But what will happen when it becomes necessary to:

• replace a water heater component;
• work on its connections;
• remove a furnace panel;
• access the blower motor;
• inspect the coil;
• work on the refrigeration connections;
• clean the drain?

A proper HVAC installation should remain serviceable for several years after commissioning.

That is why positioning the new unit takes into account not only the space available today, but also the work that may need to be carried out tomorrow.

Airflow, cold-weather heating, and efficiency: why the EVOX G3 is a good fit for a Quebec home

Computational Constant Airflow 2.0: particularly relevant when keeping existing ductwork

An important feature of the MIDEA EVOX G3 is its Computational Constant Airflow 2.0 system.

MIDEA indicates that the fan can adjust its power and speed to maintain the required airflow when system resistance changes. The manufacturer also states that it can operate at up to approximately 1.2 in. of external static pressure, with up to 60 airflow-volume adjustment levels.

This technology is particularly interesting on a project like this.

We are not starting with a new duct network designed exclusively for the new furnace. We must work with existing ducts whose sections, bends, and dimensions were determined when the house was built.

The ability to precisely adjust airflow gives us greater control during commissioning.

But a furnace capable of compensating does not make poor ductwork acceptable

This point must be made very clear.

Advanced ventilation technology does not replace a properly designed duct network.

If a return-air opening is too small, a duct is crushed, or a transition creates a major restriction, we must address the mechanical problem.

The EVOX G3 gives us greater adaptability. It does not change the fundamental principles of air distribution.

Different performance depending on the tonnage selected

The MIDEA-documented EVOX G3 line covers several capacities. The manufacturer presents systems ranging from approximately 18,000 to 54,000 BTU/h, with performance reaching up to 19 SEER2, 12.5 EER2, and 10.8 HSPF2, depending on the exact indoor and outdoor unit combination.

The MIDEA technical table includes configurations of:

• 18,000 BTUs;
• 24,000 BTUs;
• 30,000 BTUs;
• 36,000 BTUs;
• 48,000 BTUs;
• 54,000 BTUs.

For this installation in Saint-Théodore-d’Acton, the precise model is not readable in the photo. We therefore do not artificially assign a BTU rating to the installed unit.

To confirm the tonnage, efficiency, and eligibility for any financial assistance, the exact model number of the indoor unit and that of the associated outdoor heat pump must be used.

Why the number of BTUs should never be chosen based solely on square footage

Sizing a central system deserves more than a simple formula such as “X BTUs per square foot.”

We must consider, in particular:

• the building’s heat loss;
• insulation;
• windows;
• airtightness;
• ceiling height;
• the number of floors;
• exposure;
• the duct network;
• the maximum airflow these ducts can carry.

An oversized unit is not necessarily more comfortable.

In cooling, an oversized system can quickly reach the desired temperature and then shut down before sufficiently dehumidifying the home. In heating, a poor match between capacity and the distribution network can also cause fluctuations in airflow and temperature.

Performance designed for low temperatures

In a climate like Quebec’s, we place enormous importance on heating capacity when the outdoor temperature drops.

For the EVOX platform, MIDEA indicates continuous operation down to -30 °C. For the three-ton configuration used in the tests mentioned by the manufacturer, the documentation also shows up to 100% heating capacity at -25 °C, with a COP of approximately 1.9 under the published test conditions.

These data help explain why a modern central heat pump can play a much more important role in annual heating than an older generation of heat pump.

This does not mean that the capacity remains identical in all configurations. The exact performance must always be verified for the installed combination.

Auxiliary electric heating supplements the heat pump when necessary

The EVOX G3 indoor unit can accommodate a multi-stage auxiliary electric heating kit.

MIDEA indicates options of up to 25 kW, with activation and adjustment according to operating conditions.

However, we never select the maximum capacity simply because it is available.

The auxiliary heating must be selected based on:

• the heat loss calculation;
• the heat pump’s low-temperature capacity;
• the control strategy;
• the electrical panel capacity;
• the circuit breaker;
• the available wiring.

An oversized component can lead to unnecessary electrical work and significantly increase the instantaneous power demand.

R-454B: an important change in new central systems

The EVOX G3 platform presented in the documentation uses R-454B refrigerant, classified as A2L.

MIDEA indicates a global warming potential for this refrigerant of 466.

This generation of equipment requires installation and service practices tailored to it.

For our technicians, replacing an older R-410A system with a new R-454B platform is therefore not simply a matter of swapping equipment. The procedures specific to A2L equipment must be taken into account during installation, commissioning, and future service work.

Filtration up to MERV 13

MIDEA also provides for compatibility with 1-, 2-, or 4-inch filters, up to MERV 13 depending on the filtration configuration.

A higher-performance filter can help capture more:

• dust;
• pollen;
• particles;
• pet hair and dander.

However, increasing filtration can also increase resistance to airflow.

That is why the filter choice must always be compatible with the desired airflow and the duct system.

24 V thermostat or 485 communication: useful flexibility during a renovation

The EVOX G3 can operate with different control strategies. MIDEA specifically indicates compatibility with 485 communication or with certain configurations using a conventional 24 V thermostat.

During a replacement, this flexibility can be very useful when the existing wiring already runs through several walls and ceilings.

With the MIDEA communicating thermostat and the SmartHome app, the documentation also provides for features such as scheduling, comfort control, consumption monitoring, and certain remote diagnostic functions.

Subsidies and financial assistance: verify the combination, never just the brand

When a homeowner is looking for a central heat pump eligible for a subsidy in Quebec, it is important to distinguish the product line from the combination actually installed.

The name MIDEA EVOX G3 alone is not enough to confirm the amount of financial assistance.

We need to verify:

• the indoor model;
• the outdoor model;
• the applicable certified combination number;
• the performance of this combination;
• the criteria in effect at the time of the project.

This is the approach we prefer to prevent a homeowner from planning their budget around financial assistance that would not apply to their exact equipment.

What the Saint-Théodore-d’Acton photo shows better than a brochure

The technical specifications explain what the MIDEA EVOX G3 can do. The photo shows what must be done for it to work properly in a real home.

We see:

• a vertical unit integrated into an existing system;
• a new custom-fabricated metal transition;
• several changes in duct cross-section;
• a mechanical space shared with a water heater;
• an accessible drain at the bottom of the installation;
• clearances that must remain usable;
• an existing structure that we must work with rather than struggle against.

These are the details that distinguish equipment replacement from a truly professional HVAC installation.

The mistakes we seek to avoid when carrying out this type of installation

Replacing the furnace without evaluating the ductwork

A new system can only distribute the amount of air that the network is capable of carrying.

Making a transition that is too short or too restrictive

The sheet metal must allow for a reasonable transition in cross-section to avoid creating unnecessary turbulence.

Choosing capacity based solely on square footage

The building and ductwork must be considered together.

Installing the largest available electric heater

Auxiliary capacity must be sized according to actual needs and the electrical supply.

Blocking access to adjacent equipment

Both the furnace and the water heater will need to be maintained in the future.

Promising a rebate without verifying the exact models

The certification applies to a specific combination, not simply to the EVOX G3 name.

A central modernization designed around the home, not just around the equipment

This MIDEA EVOX G3 electric furnace installation in Saint-Théodore-d’Acton perfectly reflects our philosophy at AirGreen.

We never consider the furnace an independent box.

To achieve a consistent result, we must coordinate the heat pump, indoor unit, ventilation, ductwork, filtration, auxiliary heating, controls, and the building’s physical constraints.

On this project, success depended in particular on precisely adapting to the existing duct network and on a vertical layout that preserved a functional mechanical space despite the nearby water heater.

This is the same approach we apply to our central heat pump, electric furnace, and HVAC installation projects in the Greater Montreal area, including Montreal, Laval, Longueuil, the North Shore, and the South Shore, as well as in the Montérégie areas where we carry out installations.

The EVOX G3 technology offers several interesting tools. But it is the proper integration of this technology into the building that determines what occupants will actually experience: balanced airflow, stable temperature, and a central system that can be properly maintained for years.