A rooftop installation where commissioning is just as important as positioning the heat pump
In Saint-Clet, this installation of a MIDEA MIDEA28 wall-mounted heat pump led us to work directly on a flat roof already occupied by several pieces of mechanical equipment. The photo taken during our work shows a very revealing configuration: the Midea outdoor unit is installed on an elevated metal support, itself resting on long wooden bases, while our commissioning equipment is still connected to the refrigerant valves on the side of the unit.
In other words, this image does not simply show a heat pump placed on a roof. It shows an essential step in a genuine professional HVAC installation : the point at which the equipment is positioned, connected, and checked before it can be considered ready to operate.
A second outdoor unit can also be seen behind the Midea, along with several roof vents and other equipment installed on neighboring buildings. In this type of environment, each location must be chosen precisely to avoid conflicts between equipment and to preserve sufficient space for airflow and future maintenance.
Why the roof was a logical location for this MIDEA28
A wall-mounted heat pump does not necessarily need to be installed against a house’s foundation.
In some configurations, placing the outdoor unit on a roof can offer several practical advantages:
- keep mechanical equipment away from areas used by occupants;
- free up yards, decks, or passageways;
- facilitate certain refrigerant line routes to the indoor units;
- group HVAC equipment in a technical area;
- reduce the visual impact from street level.
Midea’s documentation also points out that its side-discharge outdoor units are designed in a relatively compact format and can be installed on various surfaces, including a base, a support, a deck, or a roof when the configuration allows it.
However, a rooftop installation also comes with its own constraints.
In particular, we must consider wind, drainage, snow, support stability, vibrations, and the possibility of accessing the equipment several years after installation.
An elevated unit rather than one placed directly on the gravel
In the photograph of the worksite Saint-Clet, the Midea condenser is noticeably elevated above the roof surface.
We used a metal structure that creates significant clearance beneath the heat pump. This structure rests on longitudinal bases rather than directly on the gravel.
This detail is particularly relevant for a heat pump intended for winter heating in Quebec.
During heating operation, the outdoor heat exchanger can accumulate frost. The machine must then periodically perform a defrost cycle. The water produced during this process flows beneath the unit and may then freeze when outdoor temperatures are very low.
A machine installed almost at roof level can gradually become surrounded by accumulated ice.
By raising it, we retain more space for:
- water drainage;
- air circulation;
- winter accumulation;
- inspection beneath the unit;
- maintenance work.
The support must remain stable even on a surface that is not perfectly level
Flat roofs are designed to drain water. They are therefore not necessarily perfectly level, even when they appear flat to the eye.
Gravel also creates an uneven surface.
A rooftop heat pump installation therefore requires more than simply placing the unit on four feet.
We must check the base, the stability of the whole assembly, and the machine’s final position.
The structure visible in the photo provides a much more controlled base than simply placing the unit on gravel.
Stability is important for proper mechanical operation, but it also helps reduce vibrations and noise transmitted to the building.
The photo shows a step that homeowners rarely see: refrigeration commissioning
One of the most interesting details of this installation is visible on the right side of the MIDEA28.
Our instruments are still connected to the refrigeration circuit.
The service manifold and hoses used to perform the necessary procedures before final start-up are clearly visible.
This step is essential.
A heat pump can be perfectly level, properly installed, and visually flawless, but this does not guarantee that the refrigeration circuit has been prepared correctly.
During an installation, we must specifically ensure that:
- the connections have been made correctly;
- the circuit is leak-tight;
- air and moisture have been removed from the system;
- the valves are handled correctly;
- the pipe lengths comply with the limits;
- the amount of refrigerant is compatible with the installation;
- the operating parameters meet expectations.
The quality of this commissioning will have a direct impact on the compressor and the system’s performance.
R-454B requires a specialized method
The MIDEA28 uses R-454B refrigerant, an A2L-category refrigerant. Midea’s documentation also lists an A2L dispersion system and a leak-detection sensor among the features of its newer wall-mounted series.
This means that installing a new heat pump should not be handled exactly like installing an old unit operating with a different refrigerant.
We must use methods and equipment compatible with the refrigerant used by the product.
For homeowners replacing an old heat pump, this change is important: the mere presence of old lines in the building does not automatically mean they can be kept.
Why we do not guess the BTU capacity from the photo
The Midea outdoor unit is clearly visible, as is the EnergyGuide yellow label installed on the front of the unit.
However, the exact model number is not sufficiently legible in this photograph for us to state with certainty whether it is a 9,000, 12,000, 18,000, 24,000, or 33,000 BTU unit.
We deliberately avoid assigning a BTU rating based solely on the apparent dimensions.
The MIDEA28 is a series comprising several capacities, each with its own technical specifications.
MIDEA28: heating down to -30 °C, five capacities, and specifications that actually vary by model
Five capacities available in the MIDEA28 series
Midea’s technical documentation presents the MIDEA28 as a premium wall-mounted “extreme heat pump” series, using R-454B and designed for heating down to -30 °C.
It is available in five nominal cooling capacities:
- 9,000 BTU/h;
- 12,000 BTU/h;
- 18,000 BTU/h;
- 24,000 BTU/h;
- 33,000 BTU/h.
The official combinations listed in the brochure are:
MIDEA28 9,000 BTU
- indoor unit: MSEHU-H09B-2A;
- outdoor unit: MO1HS-H09B-2A;
- AHRI: 215471380;
- cooling: 9,000 BTU/h;
- heating: 12,000 BTU/h;
- SEER2: 27,4;
- HSPF2 IV: 12,5.
MIDEA28 12,000 BTU
- indoor unit: MSEHU-H12B-2A;
- outdoor unit: MO1HS-H12B-2A;
- AHRI: 215471381;
- cooling: 12,000 BTU/h;
- heating: 12,000 BTU/h;
- SEER2: 25,4;
- HSPF2 IV: 10,5.
MIDEA28 18,000 BTU
- indoor unit: MSEHU-H18B-2A;
- outdoor unit: MO1HS-H18B-2A;
- AHRI: 215471382;
- cooling: 18,000 BTU/h;
- heating: 18,000 BTU/h;
- SEER2: 21,4;
- HSPF2 IV: 11,0.
MIDEA28 24,000 BTU
- indoor unit: MSEHU-H24B-2A;
- outdoor unit: MO1HS-H24B-2A;
- AHRI: 215471383;
- cooling: 24,000 BTU/h;
- heating: 29,000 BTU/h;
- SEER2: 21,0;
- HSPF2 IV: 13,5.
MIDEA28 33,000 BTU
- indoor unit: MSEHU-H33B-2A;
- outdoor unit: MO1HS-H33B-2A;
- AHRI: 215471384;
- cooling: 33,000 BTU/h;
- heating: 36,000 BTU/h;
- SEER2: 19,5;
- HSPF2 IV: 10,5.
These differences show why heat pump comparisons should always be based on the exact combination, rather than only in the series name.
Operation down to -30 °C for the entire range presented
All MIDEA28 capacities listed in this technical sheet have a stated operating range of -30 °C to 24 °C in heating mode.
In cooling mode, the stated range is -30 °C to 50 °C.
For an installation at Saint-Clet, this heating range is particularly relevant.
A Quebec heat pump must be evaluated as much as a heating appliance as an air conditioner.
However, two concepts must be distinguished: being able to operate at a given temperature and maintaining exactly the same capacity at all temperatures.
Available capacity varies as the outdoor temperature drops.
Performance at -15°C better shows how the system behaves in winter
Midea also provides heating capacities at -15°C, providing a more concrete indication of how each model performs in cold weather.
At this temperature, the brochure indicates:
- 9,000 BTU: 11,500 BTU/h;
- 12,000 BTU: 11,500 BTU/h;
- 18,000 BTU: 18,000 BTU/h;
- 24,000 BTU: 24,200 BTU/h;
- 33,000 BTU: 35,000 BTU/h.
The COPs published at -15°C are 1.80, 1.80, 1.92, 2.34, and 1.98, respectively.
This data is particularly useful when we assess a heat pump for heating in Saint-Clet, Montreal, Laval, Longueuil, the North Shore, or the South Shore.
The largest unit is not automatically the best
With capacities of up to 33,000 BTU, it may be tempting to choose the largest model to ensure you never run short of heating.
However, this approach can lead to oversizing.
At AirGreen, we look at:
- room dimensions;
- insulation;
- sun exposure;
- the number of windows;
- ceiling height;
- heat loss;
- the home’s layout;
- air circulation between rooms.
A properly sized heat pump can efficiently take advantage of its modulation capacity.
Midea uses variable-speed technology, allowing the compressor to adjust its operation to demand rather than operating only in on-off cycles. The manufacturer associates this operation with smaller temperature variations and more consistent comfort.
The line diameters change according to MIDEA28 capacities
Here is one of the most important aspects when MIDEA28 replaces an old heat pump.
Copper sizes vary by model:
- 9,000 BTU: 1/4 in. and 3/8 in.;
- 12,000 BTU: 1/4 in. and 3/8 in.;
- 18,000 BTU: 1/4 in. and 1/2 in.;
- 24,000 BTU: 3/8 in. and 5/8 in.;
- 33,000 BTU: 3/8 in. and 3/4 in..
The maximum lengths are respectively 82 ft, 82 ft, 98.4 ft, 164 ft, and 164 ft.
This progression clearly shows why we cannot simply reuse just any old line set.
Using the wrong copper line size can directly affect the system’s operation and reliability.
The height difference can also become significant with a rooftop installation
The brochure indicates maximum height differences of:
- 49.2 ft for the 9,000 and 12,000 BTU;
- 65.6 ft for the 18,000 BTU;
- 82 ft for the 24,000 and 33,000 BTU versions.
On a project where the outdoor unit is placed on the roof, this information can be much more important than in an installation directly behind a bungalow.
The route must be checked before finalizing the model selection.
The electrical supply also varies with capacity
The MIDEA28 units in the brochure operate at 208/230 V single-phase, 60 Hz, but their electrical requirements are not identical.
The indicated minimum allowable amperage is:
- 15 A for the 9,000 BTU unit;
- 15 A for the 12,000 BTU unit;
- 19 A for the 18,000 BTU unit;
- 24.9 A for the 24,000 BTU unit;
- 34 A for the 33,000 BTU unit.
The maximum overcurrent protections indicated are respectively 15, 15, 20, 25, and 35 A.
Therefore, a capacity should never be selected without checking the building's electrical capacity.
Sound levels must be considered both indoors and outdoors
Depending on the capacity, Midea documentation indicates outdoor sound levels ranging from 56 dB(A) to 63.5 dB(A) at the high setting.
A rooftop location can actually be useful for physically distancing the condenser from windows and relaxation areas, depending on the building's configuration.
Indoors, the MIDEA28 can operate at very low levels at reduced speeds. Some models go down to around 19.5 dB(A), while the values vary with capacity and ventilation mode.
The EnergyGuide image visible at the worksite: useful, but not sufficient on its own
The yellow label EnergyGuide is clearly visible on the unit photographed in Saint-Clet.
It is a good source of information for comparing a unit's efficiency within its category.
However, when purchasing or applying for a grant, we recommend never relying solely on a photo of this label.
The important documents remain:
- the exact indoor unit number;
- the exact outdoor unit number;
- the AHRI number;
- the performance sheet corresponding to that combination.
Grants: the exact AHRI reference is essential
The five MIDEA28 capacities described in the brochure bear the AHRI reference numbers 215471380 to 215471384 and are listed with the certification Cold Climate V6.1.
To determine actual eligibility for financial assistance such as LogisVertThe installed combination and the criteria in effect at the time of the application must be verified.
It would be incorrect to claim that a unit automatically qualifies for a specific amount simply because it bears the name MIDEA28.
Comfort features that go well beyond heating and air conditioning
The MIDEA35, 28, and 25 series include several interesting features:
- Wi-Fi control;
- ECO mode;
- Turbo function;
- night mode;
- timer;
- « Follow me »;
- silent mode;
- 8 °C heating;
- horizontal and vertical swing;
- automatic cleaning;
- humidity control;
- progressive fan control.
Midea also indicates up to 100 air-volume adjustment levels, as well as remote control with the SmartHome app in compatible configurations.
These options allow users to fine-tune comfort instead of simply choosing between a few fixed speeds.
Future maintenance was part of our criteria from the outset
A heat pump installed on the roof must remain accessible.
We must think about the technician who may eventually return to:
- clean the heat exchanger;
- check the fan;
- test the electrical parameters;
- check the refrigerant charge;
- look for a leak;
- diagnose a defrosting problem;
- replace a component.
In the photo, the Midea has working space around its main access points. The side with the refrigeration connections is accessible, which is also necessary to perform the commissioning shown in the image.
This Saint-Clet project nicely sums up our approach at AirGreen
The most interesting aspect of this installation is not just the heat pump's advertised performance.
It is the combination of the equipment, its support, and its commissioning.
On this Saint-Clet project Saint-Clet, we worked on a roof already occupied by several units. The MIDEA28 had to be positioned to maintain good airflow, remain accessible, and not sit directly on the gravel.
We installed it on a raised structure suited to the rooftop environment. We then carried out the necessary refrigeration work before final commissioning.
This is the point that the photo particularly illustrates: a A professional HVAC installation does not stop when the screws are tightened.
The connections must be tested, the circuit must be properly prepared, and the unit must be checked before handing the system over to the customer.
The MIDEA MIDEA28 is a particularly interesting solution here thanks to its ability to operate in heating mode down to -30 °C, its five available capacities, variable-speed technology, R-454B refrigerant, and numerous control functions.
At AirGreen, we apply this same level of rigor to our installations of wall-mounted heat pumps in Montreal, Laval, Longueuil, the North Shore, and the South Shore, as well as in Montérégie municipalities such as Saint-Clet.
A good heat pump is one part of the solution. Sizing, support, the refrigeration circuit, and commissioning quality determine what the unit will actually deliver once installed.