Installation of a MIDEA EVOX G3 central heat pump on a flat roof in Godmanchester, in the Haut-Saint-Laurent region
In Godmanchester, AirGreen installs a MIDEA EVOX G3 central heat pump on a raised rooftop structure: winter clearance, inverter technology, R-454B, and HVAC installation adapted to Quebec.
In summer, the outdoor unit rejects the house's heat outside.
Generic illustration of this type of installation, not a survey of this job site. Tap a number.
It captures or rejects heat outside. It sits on a level base, above the snow, with free space all around.
The insulated refrigerant lines enter the house through a sealed opening and run to the indoor coil.
A shut-off switch near the outdoor unit isolates it safely for service.
Sitting on the indoor module, it moves heat between the house air and the refrigerant.
Electric furnace or air handler: its fan pushes air through the ducts. The electric backup takes over in extreme cold.
Supply ducts bring air to the rooms; returns bring it back to the unit. Their condition matters as much as the unit's.
It protects the coil and the fan. A dirty filter cuts airflow, so it gets checked regularly.
It runs the heat pump and the backup heat. It must be compatible with the installed system.
In Godmanchester, an EVOX G3 installation where roof protection, winter clearance, and technical access become essential
This MIDEA EVOX G3 central heat pump installation in Godmanchester, in Haut-Saint-Laurent, features a configuration very different from a conventional residential ground-level installation. Here, the outdoor unit was positioned on a flat roof, above a metal structure specifically designed to keep the equipment at an appropriate height above the membrane.
The site photograph clearly shows the challenge. The large MIDEA outdoor unit with horizontal discharge rests on a rigid metal frame equipped with four legs. The condenser remains completely unobstructed at the front, while the refrigerant and electrical connections are grouped on the right side. A considerable amount of space has deliberately been maintained between the roof and the unit beneath the heat pump.
This clearance is not a matter of appearance. In our climate, a central heat pump used for heating in Godmanchester must be able to withstand snow accumulation, freezing episodes, and repeated defrost cycles without its outdoor coil becoming blocked at roof level.
The project therefore addresses an aspect we consider fundamental at AirGreen: a high-performance heat pump does not automatically result in a high-performance installation. The choice of location and the quality of the integration into the building remain decisive.
The MIDEA EVOX G3 belongs to the generation of inverter ducted central systems developed by MIDEA for heating and cooling through a duct network. The manufacturer's documentation specifically presents the EVOX G3 as a central system platform designed to facilitate the modernization of existing heating systems.
Why install a central heat pump on a roof?
At first glance, placing the condenser on the ground may seem simpler. However, it is not always the most logical location.
On certain buildings, site constraints are numerous: traffic, vegetation, windows, access, clearance around the foundation, landscaping, or the required length of the refrigerant lines. A rooftop installation can then create a much more coherent route to the indoor system.
In Godmanchester, the photographed project clearly shows one of the advantages of this approach: the outdoor unit is located in a completely separate technical area away from ground-level traffic areas.
However, a rooftop installation has its own requirements. In particular, we must consider:
- the structural capacity of the support and roof;
- the distribution of the equipment's weight;
- membrane protection;
- water drainage;
- snow accumulation;
- wind loads;
- vibrations;
- accessibility for future maintenance;
- the length and protection of the refrigerant lines;
- the clearances specified by the manufacturer.
It is therefore not enough to raise the heat pump to roof level and place it wherever space is available.
A raised metal structure that is especially important in winter
In the photo, the MIDEA EVOX G3 outdoor unit is not simply sitting on a few blocks. We can see a genuine rectangular metal structure that creates a rigid platform beneath the machine.
The resulting height is particularly advantageous.
During a defrost cycle, a heat pump can produce a considerable amount of water. When the outdoor temperature is below freezing, this water can then freeze around the unit.
On a flat roof, the issue deserves even more attention. Water must not accumulate immediately beneath the condenser to the point where it gradually forms a block of ice around its base.
By keeping the machine well above the roof surface, we leave more space for:
- the drainage of defrost water;
- maintenance beneath and around the unit;
- airflow;
- the management of winter accumulations;
- the visual inspection of the base and connections.
This is a very visible detail in this installation and one of the aspects we want to maintain in our central heat pump installations in Quebec.
A large front fan that must be able to breathe freely
The photographed façade of the EVOX G3 is dominated by a large axial fan. It is a horizontal-discharge design.
MIDEA explains that its outdoor technology combines a horizontal-discharge fan with a vertical heat exchanger to achieve more uniform airflow through the heat exchanger. The documentation also associates this design with improved heat-exchange efficiency as the outdoor temperature drops.
On our Godmanchester installation, the fan face is not oriented toward a nearby wall or parapet immediately in front of the grille.
This positioning is essential.
If the air discharged by a heat pump becomes blocked or recirculated toward its own heat exchanger, efficiency may be affected. In both heating and cooling modes, we must therefore maintain the necessary clearances in front of, behind, and around the unit according to the actual site configuration.
An EVOX G3 designed for cold winters
The appeal of this heat pump obviously does not stop at the shape of its cabinet.
For an installation located in Godmanchester, low-temperature heating capacity is a much more relevant criterion than the rated cooling capacity alone.
The MIDEA brochure advertises continuous operation down to -30 °C for the Extreme Heat EVOX G3 range. It also presents, based on tests of a three-ton MIDEA system, performance reaching 100% of the rated heating capacity at -25 °C, with a COP of approximately 1.9 under these conditions.
This figure must be interpreted correctly.
The fact that a heat pump can operate at -30 °C does not mean that all capacities in the range deliver exactly the same number of BTUs at that temperature. Performance depends on the specific model, the outdoor temperature, and the pairing with the indoor unit.
That is why we always examine the complete system data rather than relying on a single mention of “-30 °C”.
M-Powevi technology at the heart of low-temperature heating
MIDEA also describes a compressor technology called M-Powevi.
When the system operates in extreme cold, the technology uses intermediate-temperature vapor injection to increase the amount of compressed refrigerant and support heat production. The manufacturer pairs this architecture with a high-efficiency compressor motor and an optimized discharge circuit.
For a homeowner comparing a conventional central heat pump with a low-temperature central heat pump, this is exactly the type of data that deserves more attention than a general advertising claim.
In Quebec, much of a central heat pump's value is realized precisely when the mercury drops below -10 °C, -15 °C, or -20 °C.
What MIDEA EVOX G3 capacity was installed on this roof?
The EVOX G3 lineup includes several sizes and capacities.
The accompanying technical documentation presents systems of:
- 18,000 BTU/h;
- 24,000 BTU/h;
- 30,000 BTU/h;
- 36,000 BTU/h;
- 48,000 BTU/h;
- 54,000 BTU/h in rated cooling capacity, depending on the system combination considered.
In the photograph of this installation in Godmanchester, we can clearly identify the MIDEA EVOX family, but the complete nameplate is not visible enough to confirm the precise model number unambiguously.
We therefore prefer not to arbitrarily assign a tonnage to this installation.
This is precisely a good rule for any homeowner comparing quotes: the cabinet size does not reliably identify the heat pump’s capacity.
The outdoor unit number, indoor unit model, and AHRI number are much better references.
SEER2 and HSPF2 ratings that vary by capacity
The EVOX G3 lineup offers interesting efficiency levels.
For this product family, MIDEA advertises performance of up to:
- 19 SEER2;
- 12.5 EER2;
- 10.8 HSPF2;
- a COP at 5 °F of up to 2.14.
However, the precise figures vary from one capacity to another.
For example, the 30,000 BTU/h EVOX G3 central system combination presented in the documentation is listed at 17.2 SEER2, 12.0 EER2, and 10.8 HSPF2. The table also indicates a rated heating capacity of 33,000 BTU/h and approximately 33,200 BTU/h under the 5 °F/-15 °C heating condition used in the specification sheet, with a COP of 1.97.
For the 36,000 BTU/h version, MIDEA indicates 17.7 SEER2 and 10.0 HSPF2, while the larger variants display different ratings.
This reinforces an important point: we never choose a capacity simply because it displays the best SEER2 rating.
The right tonnage comes from the building, not the catalog
A central heat pump must be sized according to the building’s heat losses and gains.
An undersized unit may require excessive use of auxiliary heating during cold periods. Conversely, an oversized unit is not necessarily more comfortable. It can affect cycle duration, humidity management, and the balance of the duct network.
We therefore consider several factors:
Insulation and airtightness
Two buildings with the same floor area can have very different needs depending on the insulation of the walls, roof, and foundation, as well as the quality of the windows.
Duct network
The system must be able to deliver the required airflow without creating excessive static pressure.
Orientation and fenestration
Solar gains can significantly change the cooling demand.
Building use
A house, a multi-unit residential building, or another type of property does not necessarily have the same load profile.
This analysis is what we use as the basis for a HVAC installation, rather than a simplified BTU-per-square-foot rule.
Computational Constant Airflow 2.0: an important feature for existing ductwork
A central heat pump does not operate on its own. It depends entirely on the air distribution network.
MIDEA integrates its Computational Constant Airflow 2.0 technology into the EVOX G3, designed to adjust the fan's output and speed to better maintain airflow when system pressure changes.
The documentation shows operation of up to approximately 1.2 inches of water column of static pressure and airflow adjustment with up to 60 levels.
MIDEA states that this technology can respond to the characteristics of the duct network as well as to certain restrictions caused, for example, by a dirty filter or a partially blocked heat exchanger.
Nevertheless, we emphasize one point: no intelligent blower can turn an inadequate duct network into an excellent one.
If the returns are insufficient or certain ducts are too restrictive, we need to identify the problem instead of simply asking the motor to work harder.
R-454B: the new generation of refrigerant used by EVOX G3
The MIDEA EVOX G3 uses R-454B, an A2L refrigerant with a significantly lower global warming potential than the older refrigerants commonly used in many residential systems.
MIDEA indicates a GWP of 466 in its documentation and states that R-454B was selected for this new equipment family.
For our technicians, the arrival of R-454B also means following the installation and service methods specified for A2L refrigerants.
The refrigerant connection visible on the right side of the photographed unit is therefore an essential part of the work: joint quality, insulation, evacuation, leak testing, and commissioning must be carried out methodically.
On a roof, protecting the lines becomes even more important
In this photo from Godmanchester, the lines exit the right side of the condenser before continuing across the roof.
At this location, several risks must be anticipated: solar radiation, snow, ice, movement related to roof maintenance, and accidental mechanical damage.
We must therefore consider the entire route before connecting the equipment.
An installer should not create a refrigerant line that then becomes a permanent obstacle for the roofer or the technician responsible for servicing the heat pump.
The roof membrane must remain a priority
HVAC equipment has a significant service life, but the roof must also remain serviceable.
One of the pitfalls of rooftop installations is focusing only on the heat pump and forgetting the underlying roofing system.
We seek to avoid unnecessary pressure points, edges that could damage the membrane, and configurations that trap water around the supports.
The structure visible in this installation distributes the equipment across several support points and keeps the unit itself completely clear of the roof surface.
The result is much more favorable than a heavy condenser placed directly on the membrane.
An EVOX G3 indoor unit designed for multiple configurations
The outdoor unit is only half the system.
Inside the building, the EVOX G3 can be paired with an air handler designed for different positions. MIDEA describes a modular construction allowing several configurations, including upflow, downflow, right horizontal, left horizontal, and low-boy configurations.
This modularity becomes particularly interesting when replacing a central system in a basement or mechanical room where space is limited.
The brochure also presents indoor unit widths of approximately 14.5 to 21.5 inches, designed to facilitate certain replacements of existing furnaces. It also indicates a multivoltage architecture depending on the configurations.
Auxiliary heating: essential to consider in Quebec sizing
A central heat pump used in Quebec is generally integrated into a heating strategy that also includes an auxiliary source.
The EVOX G3 range can accommodate three-stage auxiliary electric heating of up to 25 kW, depending on the configuration. MIDEA indicates that these stages can be adjusted according to temperature and demand.
The goal is not to run the electric elements continuously.
Instead, we aim to enable the inverter heat pump to provide as much efficient heating as possible while retaining the auxiliary capacity needed when conditions or the building's load require it.
24 V thermostat or communicating system
Modernizing a central system can sometimes become costly simply because the existing control wiring is difficult to access.
The EVOX G3 offers some flexibility here.
The documentation mentions compatibility with 485 and 24 V, control-mode detection, and the possibility of wireless communication between certain MIDEA components through Sub-1 GHz modules.
Depending on the project, this can make it easier to replace an existing installation without undertaking invasive work solely for the controls.
Filtration up to MERV 13
For a central system, filtration is directly related to the operation of the indoor unit.
MIDEA offers a module compatible with 1-, 2-, or 4-inch MERV 13 filters. The documentation indicates that this filtration is intended in particular to address dust, pollen, particles, and pet hair or dander.
However, the filter's static pressure must always be taken into account. A higher-performance filter is only beneficial if the blower and ductwork are designed to operate properly with it.
This EVOX G3 project in Godmanchester summarizes several best practices for installing a central heat pump
A rooftop installation should not make future maintenance more complicated
When we complete an installation, we must already imagine the next maintenance visit.
The technical panel of the photographed unit remains accessible from the right side. The connections are not concealed behind a permanent obstacle, and the raised structure makes it possible to visually inspect the area around the base of the unit.
This is essential.
A central heat pump must be able to be diagnosed, cleaned, and repaired without dismantling half of its surroundings.
On a roof, this question is even more important because access already requires more preparation than a ground-level installation.
Snow must never be treated as a minor detail
In Godmanchester as well as Montreal, Laval, Longueuil, on the North Shore or the South Shore, we install systems designed to operate during a true Quebec winter.
An outdoor low-temperature unit installed too low loses some of the benefit of its design if it ends up surrounded by snow.
The substantial metal support visible here creates a very valuable safety margin between the unit and the roof.
It also facilitates the management of water from defrost cycles and keeps the outdoor coil better clear.
LogisVert: verify the pairing and AHRI number before advertising a rebate
The issue of Hydro-Québec LogisVert rebates naturally comes up when purchasing a central heat pump.
For heat pumps installed on or after November 26, 2025, Hydro-Québec indicates that the units covered by the Efficient Heat Pump program must be ENERGY STAR certified to be eligible. The lists and amounts may vary depending on the installation period.
The MIDEA brochure states, for its part, that the range presented exceeds the ENERGY STAR Most Efficient criteria applicable to this product family.
However, this is not a reason to automatically advertise a specific amount for every EVOX G3.
For an actual application, you must identify the exact pairing of the indoor and outdoor units and its AHRI number, then check the Hydro-Québec list applicable on the date of the work. Hydro-Québec specifically recommends searching by AHRI number and states that an application should normally be submitted within nine months of installation.
This verification prevents one of the most common mistakes: choosing equipment solely based on an announced rebate amount without confirming that the combination actually installed matches the eligible listing.
The mistakes we seek to avoid when installing a central rooftop system
This Godmanchester project helps summarize several practical points.
Installing the condenser too close to the roof.
This increases vulnerability to snow accumulation and complicates the management of defrost water.
Neglecting the roof membrane.
The supports and piping must not unnecessarily create points of deterioration.
Block the discharge side.
A horizontal-discharge unit must retain the space needed to move its substantial volume of air.
Forgetting access to the service panel.
An installation that seems compact today can become extremely expensive to service if no technician can properly access the components.
Choosing the tonnage based on floor area alone.
The heat load, ductwork, insulation, and airflow are just as important.
Confusing the maximum performance of a product range with that of the installed model.
“Up to 19 SEER2” does not mean that every EVOX G3 has exactly a SEER2 rating of 19.
Announcing a subsidy without confirming the AHRI.
The exact combination must be verified.
Why this project represents the way we work at AirGreen
This MIDEA EVOX G3 central heat pump installation in Godmanchester is not interesting simply because it uses recent equipment.
It is especially so because the location required careful installation planning.
A flat roof changes the priorities. You have to consider wind, snow, defrost water, the membrane, access, and future service work. The large metal structure visible beneath the heat pump addresses several of these constraints precisely.
The EVOX G3 technology then brings the benefits of the system itself: inverter compressor, low-temperature heating down to -30 °C depending on the range, R-454B, horizontal discharge, adaptive indoor airflow, 24 V or communicating compatibility, advanced filtration, and modular indoor unit design.
But we always come back to the same principle: the manufacturer’s specifications must be supported by an installation capable of making the most of them.
At AirGreen, we apply this approach in our central heat pump projects in Montreal, Laval, Longueuil, on the North Shore, on the South Shore, and elsewhere in Greater Montreal and Montérégie. The type of building changes, the route of the lines changes, and the location of the condenser changes, but our objective remains the same: to achieve a durable, accessible HVAC installation suited to Quebec’s climate.
In Godmanchester, this translated into a MIDEA EVOX G3 installed well above a flat roof, on a sturdy structure, with generous front clearance and access to the connections maintained.
This is exactly the kind of detail that does not appear in a brochure’s SEER2 rating, but that can make a big difference during the many winters the heat pump will spend on this roof.
How it goes, from the first call to the end
The main steps of this kind of job at AirGreen. Every house has its quirks: the estimate brings them out.
We look at the ducts, the current indoor module, the electrical panel and the planned spot for the outdoor unit.
The equipment combination, capacity and price, in writing. We check whether the combination qualifies for assistance programs.
Access protected, old unit disconnected and removed when it is being replaced.
Electric furnace or air handler, with its coil, connected to the supply and return ducts.
On a level base, raised above the snow, with free space all around.
Insulated, they enter through a sealed opening and run to the indoor coil.
Dedicated circuits, accessible disconnect, a thermostat that works with the heat pump and the backup heat.
Leak test, vacuum, start-up, airflow check and a test of both modes.
Filter, thermostat, backup heat in extreme cold: what to know before winter.
- The on-site estimateWe look at the ducts, the current indoor module, the electrical panel and the planned spot for the outdoor unit.
- The quoteThe equipment combination, capacity and price, in writing. We check whether the combination qualifies for assistance programs.
- Getting readyAccess protected, old unit disconnected and removed when it is being replaced.
- The indoor moduleElectric furnace or air handler, with its coil, connected to the supply and return ducts.
- The outdoor unitOn a level base, raised above the snow, with free space all around.
- The refrigerant linesInsulated, they enter through a sealed opening and run to the indoor coil.
- Electrical and thermostatDedicated circuits, accessible disconnect, a thermostat that works with the heat pump and the backup heat.
- Tests and start-upLeak test, vacuum, start-up, airflow check and a test of both modes.
- The walkthroughFilter, thermostat, backup heat in extreme cold: what to know before winter.
What the unit delivers when it is cold
The range as published on airgreen.ca: pick a size to see its capacity in deep cold.
| Size | Heating at −8 °C | Heating at −15 °C | Coldest certified point | COP at −15 °C | SEER | HSPF | Indicative LogisVert aid |
|---|---|---|---|---|---|---|---|
| Midea EVOX G3 · 1.5 tons | 14,700 | 18,600 | −30 °C: 11,800 | 2.12 | 19.0 | 10.1 | $1,764 |
| Midea EVOX G3 · 2 tons | 20,800 | 20,600 | −30 °C: 12,100 | 2.14 | 18.6 | 10.0 | $2,496 |
| Midea EVOX G3 · 2.5 tons | 24,000 | 33,200 | −30 °C: 17,900 | 1.97 | 17.2 | 10.8 | $2,880 |
| Midea EVOX G3 · 3 tons | 33,000 | 37,400 | −30 °C: 27,600 | 1.9 | 18.0 | 10.0 | $3,960 |
| Midea EVOX G3 · 4 tons | 39,500 | 48,000 | −30 °C: 27,200 | 2.0 | 17.5 | 9.5 | $4,740 |
| Midea EVOX G3 · 5 tons | 45,000 | 54,000 | −30 °C: 37,300 | 1.9 | 17.5 | 9.5 | $5,400 |
Data read live from the airgreen.ca page of each size (NEEP / AHRI certified performance). When the title names the installed size, it is highlighted; otherwise the whole range is shown. The aid shown is today’s, using Hydro-Québec’s rule ($120 per 1,000 BTU/h at −8 °C); amounts quoted in the article date from its publication. Only Hydro-Québec confirms the assistance granted.
And at your place?
Two quick checks with real numbers: what heat costs, and what your current heaters add up to in BTU/h.
Baseboards and electric furnaces turn 1 kWh of electricity into 1 kWh of heat. A heat pump delivers more: that is its COP. At Hydro-Québec’s rate D (11.142¢/kWh above 40 kWh a day, since 1 April 2026):
Hydro-Québec: a heat pump can be up to three times more efficient than baseboards for heating in the colder months.
Estimate per kWh of heat, at the chosen temperature, using the certified COP from the product page. Taxes, access charge and backup heat not included.
Conversion: 1 W = 3.412 BTU/h. An indication, not a load calculation: baseboards and furnaces are often stronger than the real need, and they can stay as backup. AirGreen confirms the capacity on site.
What to do, season by season
Three habits per season for this unit. They take a few minutes and prevent many calls.
- Check the indoor module's filter.
- Clear winter debris from the outdoor unit.
- Test cooling before the heat arrives.
- Check the filter more often in peak season.
- Keep registers and returns clear.
- Watch condensate drainage near the coil.
- Change or clean the filter.
- Test heating and backup heat before the cold.
- Book periodic maintenance.
- Clear snow around the outdoor unit.
- Store nothing in front of the indoor module.
- Note any unusual noise or smell and call us.
Which type of equipment for your project?
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Four mistakes we do not make
Flip each card to see what we do instead.
What people ask us about this kind of work
Can I keep my current ducts?
What happens in extreme cold?
Furnace, air handler, ducted: what is the difference?
Are there grants?
Do I need a permit?
How much can I save?
How is the LogisVert assistance calculated?
Will my current thermostat work?
Central or wall units: which one?
Does AirGreen hold the required licences?
Is the estimate free?
No question matches. Write to us: we answer.
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Text and photo: a real AirGreen Climatisation & Chauffage job. The diagrams are generic illustrations of the type of installation, not a survey of this job site. Sources of the added figures: airgreen.ca product pages (NEEP / AHRI performance), Hydro-Québec (Heat pumps page, LogisVert, read on 13 October 2026), Régie de l’énergie (rate D as of 1 April 2026).