Replacing an old heat pump without letting its former location dictate the new installation
This installation of MIDEA MIDEA28 wall-mounted heat pump in Saint-Lazare perfectly illustrates a situation we regularly encounter at AirGreen: replacing an old unit whose dimensions, wall penetration, and position no longer necessarily correspond to those of the new heat pump.
The job-site photograph tells much of the story. The new Midea indoor unit is installed high up, near the ceiling. Beneath it, the rectangular outline of the old unit, several former mounting points, and a circular opening in the wall toward the right are clearly visible.
In other words, this was not an installation on a blank wall.
We had to work with what was already there while avoiding a common mistake when replacing a unit: installing the new appliance in exactly the same place solely to cover the marks left by the old one.
At AirGreen, the priority remains the operation of the new heat pump. The location must be compatible with the dimensions of the new model, allow good air circulation, meet the required clearances, and provide future access forHVAC maintenance.
The wall painting and finishing work can then be completed separately. It is preferable to redo a small finishing area than to compromise the performance or future accessibility of a heat pump for years simply to hide an old outline.
A height difference immediately visible on the job site
The old unit was positioned noticeably lower.
The new MIDEA28 is positioned closer to the ceiling, revealing the entire area that was previously covered. This detail makes the project particularly interesting because it provides a concrete understanding of what happens when replacing a a wall-mounted air conditioner or wall-mounted heat pump from another generation.
Head dimensions are not standardized between manufacturers, or even among the different capacities within the same series.
The MIDEA28 is available in several capacities, and the width of the indoor unit varies considerably depending on the capacity. Midea documentation lists indoor units measuring 9,000, 12,000, 18,000, 24,000, and 33,000 BTU/h.
The 9,000 and 12,000 BTU/h models measure approximately 31.30 in wide, the 18,000 BTU/h model approximately 37.99 in, while the 24,000 and 33,000 BTU/h models reach approximately 44.88 in.
A few inches can therefore completely change how much of the old unit’s marks a new head covers—or fails to cover.
Why we do not systematically seek to reuse the old hole
The circular opening visible in the lower-right part of the old footprint is another important element of the project.
When replacing a unit, a homeowner may naturally think: “The hole is already there, so why not simply run the new lines through the same place?”
In practice, we must first check whether this old opening matches the new configuration.
The exit point depends in particular on:
- the position of the new unit;
- the design of its mounting plate;
- the side selected for the connections;
- the diameter of the refrigerant lines;
- the drain routing;
- the slope required for condensate drainage;
- the condition of the existing opening;
- how the lines connect to the outdoor unit.
The Midea brochure notes that a ductless system connects the indoor and outdoor units through a relatively compact wall opening and that the refrigerant lines provide significant installation flexibility.
This flexibility makes it possible to install the new head in the most logical location instead of being constrained by the choices made during the initial installation.
Saint-Lazare: choosing a heat pump with serious consideration for winter heating
In a project in Saint-Lazare, heating performance is a central criterion.
A heat pump used in Vaudreuil-Soulanges must obviously cool efficiently during the summer, but above all it must be able to continue providing heat when temperatures drop well below freezing.
The MIDEA28 is presented by Midea as a premium wall-mounted series of the extreme heat pump. It uses the refrigerant R-454B, bears the designation Cold Climate V6.1 in the documentation provided and is rated for heating operation down to -30°C.
The published operating range for the five MIDEA28 capacities extends from -30°C to 24°C in heating mode and -30°C to 50°C in cooling mode.
This makes it a particularly relevant range when a homeowner is looking for a wall-mounted heat pump for cold climates.
MIDEA28: five capacities for very different needs
Unlike the MIDEA35, which is offered in fewer capacities in the brochure provided, the MIDEA28 covers a particularly wide range.
Midea lists:
- 9,000 BTU/h;
- 12,000 BTU/h;
- 18,000 BTU/h;
- 24,000 BTU/h;
- 33,000 BTU/h.
The corresponding AHRI reference numbers are respectively 215471380, 215471381, 215471382, 215471383 and 215471384.
This variety allows us to better adapt the system to the actual dimensions and heat losses of the area served.
In the photograph of this installation in Saint-Lazare, the technical label on the indoor unit is visible, but its text is not clear enough to confirm with certainty the exact capacity installed. We therefore do not arbitrarily assign it a BTU rating.
This is an important point: MIDEA28 is the name of a series, not a single capacity.
Up to 27.4 SEER2, but not across all capacities
The maximum advertised rating for the series is 27.4 SEER2.
It corresponds to the 9,000 BTU/h model.
The published SEER2 ratings are:
- 9,000 BTU/h: 27.4 SEER2;
- 12,000 BTU/h: 25.4 SEER2;
- 18,000 BTU/h: 21.4 SEER2;
- 24,000 BTU/h: 21.0 SEER2;
- 33,000 BTU/h: 19.5 SEER2.
The Region IV HSPF2 values are, respectively, 12.5, 10.5, 11.0, 13.5 and 10.5.
This variation explains why we always recommend comparing specific model numbers, rather than just product-line names accompanied by a maximum performance figure.
This MIDEA28 replacement in Saint-Lazare shows the details that matter after the quote has been signed
Performance at -15°C helps show how it really behaves in winter
Saying that a heat pump operates down to -30°C is not enough to understand its capacity when it is actually very cold.
Midea specifically publishes heating data at -15°C for each MIDEA28.
At this temperature, the advertised rated capacity is:
- 11,500 BTU/h for the 9,000 model;
- 11,500 BTU/h for the 12,000;
- 18,000 BTU/h for the 18,000;
- 24,200 BTU/h for the 24,000;
- 35,000 BTU/h for the 33,000.
The associated COPs are 1.80, 1.80, 1.92, 2.34 and 1.98.
These figures show why sizing must take heating demand into account.
For example, a model rated at 33,000 BTU/h for cooling has a rated heating capacity of 36,000 BTU/h in the general data and 35,000 BTU/h at -15°C according to the table provided.
This kind of information is much more relevant to a Quebec home than a simple comparison based on floor area.
A larger heat pump is not automatically a better heat pump
The capacity selected must match the building.
We assess, among other things:
- the area actually served;
- insulation;
- windows;
- ceiling height;
- the number of floors;
- the opening between rooms;
- heat loss;
- the existing heating system;
- the indoor unit’s location;
- the heat pump’s performance at winter temperatures.
An oversized unit can operate in a way that is less comfortable than a properly sized heat pump.
Maximum capacity is therefore not our goal. The appropriate capacity is.
Variable-speed technology: the role of modulation
Midea uses variable-speed technology that allows the compressor to adjust its operation according to demand.
The brochure explains that this technology allows the compressor to operate continuously as needs change and reduce temperature variations compared with a conventional system that operates primarily in on-off cycles.
In a properly sized installation, this allows the system to reduce its output when the home requires less heating or cooling, rather than always having to operate at maximum capacity.
For the homeowner, the goal is more consistent comfort and operation better suited to the actual load.
Indoor noise levels vary significantly depending on capacity
A wall-mounted heat pump is installed directly in the living space. Its noise level therefore matters just as much as that of the outdoor unit.
For the MIDEA28, the documentation indicates minimum levels that can drop to approximately 19.5 dB(A) on the 9,000, 12,000, and 18,000 BTU/h models. The 24,000 BTU/h model has a value of 16 dB(A) in the published quiet-operation data, while the 33,000 BTU/h model is logically noisier given its much higher airflow rate.
This criterion becomes particularly important when the head is installed near a bedroom, living room, or workspace.
The airflow rate must match the volume being treated
The higher capacities also have much higher airflow rates.
Midea specifically indicates up to approximately 865 CFM in Turbo mode for the 33,000 BTU/h indoor unit, compared with approximately 441 CFM for the 9,000 and 12,000 BTU/h capacities.
This explains why the location of a large unit deserves particular consideration.
A high airflow rate can be very useful in a large open space, but less pleasant if the head blows directly toward an area where occupants remain seated.
At our Saint-Lazare job site, the repositioning shown in the photo precisely illustrates the importance of considering the new unit rather than automatically reproducing the previous configuration.
Different lines depending on the BTU rating
The MIDEA28 offers a very wide range, and this variety is reflected in the dimensions of the refrigerant lines.
According to the documentation:
- 9,000 and 12,000 BTU/h: 1/4 in. and 3/8 in.;
- 18,000 BTU/h: 1/4 in. and 1/2 in.;
- 24,000 BTU/h: 3/8 in. and 5/8 in.;
- 33,000 BTU/h: 3/8 in. and 3/4 in..
This is a fundamental point in a replacement project like this one.
The mere fact that pipes already exist behind the old unit does not mean they are the diameter required for the new capacity.
A mistake to avoid: adapting the new heat pump to the old lines
A homeowner may want to keep the old lines at all costs to simplify the project.
This decision should never be made before identifying:
- their diameter;
- their condition;
- their length;
- the capacity of the new system;
- the manufacturer’s requirements.
In a professional HVAC installation, it is the selected system that defines the refrigeration-circuit requirements, not the other way around.
Maximum line-set length: 82 to 164 feet depending on the model
The permitted length also varies according to capacity.
Midea indicates:
- 82 ft for the 9,000 and 12,000 BTU/h models;
- 98.4 ft for the 18,000 BTU/h model;
- 164 ft for the 24,000 and 33,000 BTU/h models.
The maximum height differences range from 49.2 ft to 82 ft depending on the model.
This flexibility makes it possible to position the indoor head according to comfort needs and the outdoor unit according to site constraints, provided the project stays within the specified limits.
R-454B and A2L leak detection
The MIDEA28 series operates with R-454B refrigerant, as indicated in the brochure’s technical table.
Midea also mentions an A2L refrigerant leak detection sensor as well as dual temperature and humidity monitoring for the applicable series.
This means the installation must be carried out according to the requirements applicable to this new generation of equipment.
Replacing an old heat pump is therefore not always a matter of simply “removing and replacing.”
Electrical requirements vary according to capacity
All the MIDEA28 models presented operate at 208/230 V, single-phase, 60 Hz.
For the outdoor unit, the minimum allowable amperage is specified at:
- 15 A for the 9,000 BTU/h;
- 15 A for the 12,000;
- 19 A for the 18,000;
- 24.9 A for the 24,000;
- 34 A for the 33,000.
The corresponding maximum protection ratings are 15, 15, 20, 25, and 35 A.
This progression once again demonstrates why the exact capacity must be identified before confirming compatibility with the existing electrical circuit.
Comfort features that go beyond simple temperature adjustment
The MIDEA28 shares numerous control functions with the MIDEA35 and MIDEA25 series.
The documentation notably mentions:
- ECO mode;
- Turbo;
- fan-speed adjustment;
- Wi-Fi control;
- night mode;
- timer;
- child lock;
- function Follow Me;
- automatic cleaning;
- quiet mode;
- heating at 8 °C;
- horizontal and vertical swing;
- optional wired controller;
- smart sensor;
- humidity sensor.
Midea also indicates up to 100 air-flow settings, allowing more precise modulation of ventilation.
The Follow Me function for measuring the temperature somewhere other than directly at the head
The function Follow Me is particularly interesting in certain spaces.
The remote control has a temperature sensor. When used with this function, the heat pump can take the temperature measured near the remote control into account rather than relying solely on the conditions directly around the wall-mounted head.
This can contribute to more representative regulation when the unit is installed very high, as in this Saint-Lazare installation.
8 °C heating for periods of vacancy
The MIDEA28 also offers a hold function at 8 °C.
According to Midea documentation, this function maintains a minimum heating temperature to help prevent freezing during an extended period of vacancy in cold weather.
This is a practical feature for certain homes, garages, or spaces that do not need to be kept at a normal temperature continuously.
A design that facilitates thorough cleaning
Midea indicates that the blower wheel is removable on the MIDEA35, MIDEA28, and MIDEA25 series.
This design provides better access to the inside of the head during deep cleaning.
For us, this is a tangible advantage.
The filters can be regularly maintained by the homeowner, but over the years, dust and contaminants can also accumulate on the heat exchanger, blower wheel, and internal surfaces.
A HVAC maintenance properly helps maintain normal airflow and prevent excessive dirt buildup.
The visible marks on this wall also offer homeowners practical advice
A photo of this installation in Saint-Lazare clearly shows what happens when an old unit is lower or has different dimensions.
The footprint of the old unit remains visible after the replacement.
This does not mean that the installation of the new heat pump is incomplete from an HVAC standpoint. Painting, plasterwork, and architectural finishing are separate from the technical positioning of the unit.
Before a replacement, we therefore recommend planning for the possibility of:
- fill in old holes;
- repair certain mounting points;
- touch up the plaster;
- repaint the area formerly concealed by the old unit.
The final result will then be clean without requiring the installer to compromise the position of the new equipment.
Midea Warranty: an important factor in calculating long-term value
The Midea brochure provided presents limited warranties for the residential sector 12 years on the compressor, 12 years on parts, and 10 years on labor, according to the applicable conditions.
As with any heat pump warranty, you must verify the registration conditions and the exact terms applicable to the installation.
However, a unit with good coverage represents a much more attractive proposition when the installation itself is done correctly from the outset.
MIDEA28 and rebates: the AHRI number must be verified before confirming an amount
The brochure identifies the five MIDEA28 combinations with specific AHRI numbers and lists them under the Cold Climate V6.1.
However, it does not specify a financial assistance amount for this Saint-Lazare installation.
For an application LogisVert or any other program available in Quebec, we must therefore verify the exact combination separately, as well as the rules in effect at the time of application.
We avoid promising a rebate based solely on the series name.
Why this Saint-Lazare installation reflects AirGreen’s approach so well
The photograph could be summed up in one sentence: a new Midea heat pump installed above the old footprint.
To us, it tells a much bigger story.
It shows that an HVAC replacement sometimes requires starting from the logic of the new machine rather than reproducing that of the old installation.
We have a new unit format, new refrigeration specifications, and new equipment using R-454B, several possible capacities, and precise air circulation and accessibility requirements.
The technical result must take priority over the desire to immediately hide every trace of the old installation.
This is the approach we apply to our wall-mounted heat pumps in Saint-Lazare, Montreal, Laval, Longueuil, the North Shore, and the South Shore.
The MIDEA28 offers an especially wide capacity range, with efficiency of up to 27.4 SEER2, an HSPF2 of up to 13,5, heating operation down to -30°C and several advanced control functions.
But brochure figures can never replace a carefully planned installation.
On this Saint-Lazare project, the most important detail may be precisely the one visible beneath the new head: the mark left by the old unit. It shows that, when replacing it, we chose to prioritize the new HVAC installationits placement and future operation, rather than forcing a modern heat pump to occupy exactly the same space as an older system that had neither the same dimensions nor the same requirements.