Two indoor units positioned to better distribute heating and cooling throughout the room
This wall-mounted heat pump installation in Charlemagne was carried out in a large rectangular room whose layout required more than simply choosing a wall. The job-site photograph shows a long, relatively narrow space, with several windows at one end, electric baseboards, wall-mounted fans, a ceiling fitted with numerous recessed lights, and a work area still protected by tarps.
Our team installed Hitachi airHome 400 indoor units at different points in the room to improve air distribution along its entire length. One unit is visible near the opposite end, while a second, larger unit is installed in the front part of the space.
This layout addresses a common problem in large, elongated rooms: a single heat pump placed at one end can produce a comfortable temperature nearby while leaving a significant comfort difference several metres farther away. Partitions, furniture, wall-mounted fans, windows, and even occupants’ movements influence the actual airflow.
In this project, we therefore had to consider the space as a whole. The goal was to create complementary air-distribution zones without directing the two units toward each other or obstructing the walls used by the occupants.
A long room that required a precise air-distribution strategy
Rectangular rooms pose a particular challenge for ductless heating and cooling. Air blown by a wall-mounted unit moves efficiently forward, but gradually loses speed as it travels through the room.
If a heat pump is installed too far from an occupied area, the temperature shown on the remote control may be reached near the unit without providing uniform comfort throughout the rest of the space.
The photograph makes it possible to observe several important features:
- a room whose length is significantly greater than its width;
- several windows located at one end;
- an exterior door or a glazed opening;
- existing electric baseboards;
- wall-mounted fans that previously helped circulate the air;
- a ceiling that is fairly low compared with the total length of the space;
- few transverse walls to interrupt air movement.
In this configuration, using two indoor units makes it possible to address different parts of the space more directly. Each unit can modulate its operation according to the demand in its zone, rather than forcing a single heat pump to operate at high speed in an attempt to reach the opposite end.
Positioning the first unit near the glazed area
The unit visible at the back of the room was installed near the windows and door. This area may experience significant heat gains in summer and more pronounced heat losses in winter.
Even when the windows are high quality, their thermal resistance generally remains different from that of an insulated wall. Possible air infiltration around the openings can also affect comfort.
A unit installed near this part of the building can respond more quickly to temperature variations caused by:
- solar radiation;
- frequent opening of a door;
- heat loss near the glazing;
- drafts;
- variable occupancy of the area;
- summer humidity.
However, the positioning had to remain far enough from the windows so that the unit could be mounted on a stable section of wall and the piping route could maintain an appropriate slope.
The second Hitachi airHome 400 to complete the room’s coverage
The unit in the foreground is installed higher up on the same side of the space. Its air discharge louver is open, making it possible to see the general direction of the airflow toward the center of the room.
This second heat pump handles the portion of the space that would have been more difficult to reach with the unit placed near the windows.
The distance between the two units was chosen to create more uniform coverage without concentrating all the capacity in one place. The goal was not simply to multiply the number of units, but to assign each one a logical work area.
When a configuration includes multiple wall-mounted units, we must avoid several mistakes:
- installing the units too close to each other;
- directing airflow in opposite directions;
- placing all temperature sensors in the same area;
- overlooking differences in exposure between the ends of the room;
- oversizing the total capacity;
- forgetting that each unit requires reliable drainage;
- create a piping route that is difficult to maintain.
Good design must simultaneously consider total capacity, the modulation of each unit, and the actual air circulation in the space.
A line route installed near the ceiling
The photo shows an indoor pipe cover running along the upper part of the wall, near the ceiling. This route groups the refrigerant lines, communication wiring, and drainage components associated with the indoor units.
Placing the pipe cover near the ceiling offers several advantages in a long room:
- it leaves the lower portions of the wall clear;
- it reduces the risk of collisions with furniture;
- it follows an existing architectural line;
- it facilitates passage between multiple units;
- it limits the visual impact of the system;
- it maintains a controlled slope when the configuration allows.
The visible route includes horizontal sections, fittings, and changes in direction near the units. These elements must be installed precisely to avoid an uneven finish or strain on the copper pipes.
We must also plan for future access. A pipe cover must not become a permanent structure that cannot be opened. The covers must be removable to inspect the lines or work on a connection if necessary.
The proximity of the recessed light fixtures and the ceiling
This room's ceiling includes several recessed light fixtures. Before drilling or securing the lines near this area, we must consider the possible location of electrical cables, junction boxes, and the ceiling structure.
Even when the light fixtures appear to be far from the wall, their wiring may run through the area where the heat pump lines need to pass.
We therefore check the route before making any openings. This precaution helps avoid:
- damage to an electrical cable;
- interference with a light fixture;
- a hole drilled in a structural element;
- a conflict with an existing pipe;
- unnecessary ceiling repairs;
- a more complex refrigerant line route than expected.
The presence of a finished ceiling also requires particular attention to keeping the worksite clean. The work areas visible in the photograph were protected to reduce dust and damage during installation.
An installation carried out during renovation work
The room was clearly undergoing renovation when the photograph was taken. The floor is protected with drop cloths, a ladder is still in place, and several tools are visible.
Carrying out the HVAC installation during renovations can be advantageous, because certain routes are more accessible and finishing work can be coordinated with the other trades.
This coordination makes it possible, among other things, to:
- plan penetrations before the final painting;
- conceal certain lines;
- protect newly finished walls;
- adapt the furniture to the new equipment location;
- choose the electrical circuits before closing up the surfaces;
- correct outdated installations that are no longer suitable.
However, the heat pump must be protected from construction dust contamination. An indoor unit should not be used as a ventilation system during sanding, wood cutting, or drywall work.
Fine dust can reach:
- the filters;
- the heat exchanger;
- the blower wheel;
- the condensate pan;
- the sensors;
- the louvers.
When work continues after installation, we recommend protecting the equipment and putting it into service only once the main dust has been removed.
The Hitachi airHome 400 range and its available capacities
The Hitachi airHome 400 is available in several capacities, ranging from 9,000 to 36,000 BTU/h according to the manufacturer's documentation. The image does not make it possible to confirm with certainty the individual capacity of the two units installed in Charlemagne. This must be verified using the nameplates, model numbers, or project file.
Depending on the selected combination, the range includes:
- nominal cooling capacities from 9,000 to 33,000 BTU/h;
- nominal heating capacities from 10,000 to 35,000 BTU/h;
- cooling efficiency of up to 20.0 TRÉS2;
- heating efficiency of up to 10.5 CPSC2 in Region 4 for certain capacities;
- operation with the refrigerant R32;
- a published heating operating range down to approximately -20.5 °C;
- indoor sound levels starting at approximately 29 dB(A) for certain models;
- optional Wi-Fi compatibility;
- the FrostWash function on the indoor unit.
Hitachi documentation also indicates that certain indoor units in the RAK-DJ-RHAA series can be used with single-zone airHome 400 systems as well as with certain multizone configurations. Exact compatibility must always be confirmed based on the indoor models, outdoor unit, and combinations approved by the manufacturer.
Why we do not determine BTUs based solely on the length of the room
A large room does not automatically require the highest available capacity. Sizing must be based on actual heating and cooling needs.
Several factors had to be evaluated for this project in Charlemagne:
- total floor area;
- ceiling height;
- the number of windows;
- sun exposure;
- wall insulation;
- the number of occupants;
- how often doors are opened;
- heat-producing appliances;
- the presence of electric baseboard heaters;
- the option of using both units simultaneously or separately.
An oversized system can reach its setpoint too quickly. This sometimes shortens cycle durations and limits dehumidification in summer.
Conversely, insufficient capacity can force the units to run continuously, especially during very cold or very hot periods.
The advantage of several well-distributed units is that they can adapt their output to the layout of the space rather than concentrating a high capacity at a single point.
Inverter modulation for more stable operation
Hitachi airHome 400 heat pumps use Vector DC Inverter technology. The compressor can adjust its speed according to demand instead of operating only at full capacity and then stopping completely.
In a large room with two indoor units, this modulation can help maintain a more consistent temperature.
When the space is far from the setpoint, the units can operate at a higher capacity. Once the temperature has stabilized, they gradually reduce their output.
This approach can provide several benefits:
- fewer temperature fluctuations;
- energy consumption suited to demand;
- fewer abrupt starts;
- quieter operation;
- better dehumidification;
- a more balanced distribution between the zones.
However, temperature settings must remain consistent. If two units serve the same large space, very different settings can lead to inefficient operation or conflicting comfort zones.
The role of the existing wall-mounted fans
The photograph shows several wall-mounted fans installed along the room. They appear to have been used to promote air movement before or during the work.
These fans can sometimes help redistribute air, but they do not replace proper heat pump placement.
A fan pointed directly at an indoor unit can also interfere with its sensor reading or push air toward an undesired area.
After commissioning, it may be useful to adjust their operation according to requirements. In many cases, newer wall-mounted units already offer multiple speeds and motorized louvers capable of providing sufficient air circulation.
The goal is to avoid creating uncomfortable drafts. The combination of the heat pumps and fans should promote an even temperature, rather than increase the feeling of airflow in occupied areas.
FrostWash and indoor heat exchanger maintenance
The FrostWash function on the Hitachi airHome 400 uses a freezing and thawing process to help capture and remove certain impurities present on the indoor heat exchanger.
In a room that can accommodate several occupants or be used for extended periods, this function can help maintain airflow.
The lineup also offers the Mold Guard function, which helps dry the internal components after certain cooling cycles.
However, these functions do not replace a regular maintenance program. Each unit must be checked separately.
Maintenance includes, among other things:
- cleaning the filters;
- inspecting the heat exchangers;
- checking the drains;
- cleaning the condensate pans;
- inspecting the blower wheels;
- checking the louvers;
- checking the connections.
In an installation with multiple units, a unit that is farther away or used less frequently can easily be overlooked. Filters should therefore be maintained according to their actual condition, not solely based on the estimated number of operating hours.
Key lessons from this Hitachi installation in Charlemagne
This project demonstrates that a large room should not be treated as a simple square space. Its length, openings, use, and heat sources should guide the placement of the units.
Mistakes to avoid when installing multiple wall-mounted units
For a similar configuration, we specifically avoid:
- install both units at the same end;
- point their air jets directly at each other;
- select the capacity based solely on the floor area;
- forget thermal losses near the windows;
- install the lines without adequate slope;
- running pipes near light fixtures without checking;
- making the filters difficult to access;
- using the units during dusty work;
- setting contradictory temperatures;
- keeping fans that interfere with the sensors;
- neglecting maintenance on a less visible unit;
- leaving the line-set covers unfinished.
A successful installation must also preserve the appearance of the room. The line-set cover should follow a coherent path, the units must be level, and the vertical runs should remain as discreet as possible.
The checks performed during commissioning
After installation, we check each unit separately, followed by their simultaneous operation.
Our checks include:
- the stability of the wall plates;
- the level of the units;
- the operation of the louvers;
- the different fan speeds;
- cooling startup;
- heating startup when conditions permit;
- the temperature of the discharged air;
- the drainage from each drain line;
- the absence of abnormal vibration;
- communication with the outdoor unit;
- the response of the remote controls;
- air distribution throughout the room.
We also explain to the owner how to use the units together. In a large open space, it is often preferable to maintain similar settings and let Inverter technology gradually modulate the capacity.
An installation suited to the large spaces of Charlemagne and Greater Montréal
At AirGreen, we install wall-mounted heat pumps in Charlemagne, as well as in Montréal, Laval, Longueuil, the North Shore, and the South Shore.
Large spaces, open areas, and elongated rooms require special analysis. A poorly positioned unit may perform well on paper without actually providing uniform temperatures.
This installation of several Hitachi airHome 400 units demonstrates the importance of distributing the equipment according to the shape of the space. The route near the ceiling groups the lines together without occupying the usable parts of the wall, while the two units serve complementary areas.
The owner thus benefits from a system capable of heating, cooling, and dehumidifying a space that would be difficult to handle with a single wall-mounted unit. The quality of the result depends on selecting the right capacities, the distance between the units, the airflow direction, drainage, and coordination with the renovation work.