Four zones, a century-old brick wall, and a single outdoor unit: the calculation that determines everything
At Saint-Jean-Baptiste, at the foot of Mount Saint-Hilaire, many residences have never had a duct network. Electric baseboard heating, a supplemental wood stove, exposed masonry walls, irregular ceilings, and partitions that do not follow the rules of a modern floor plan. For these homes, a multizone heat pump is often the only serious path to balanced comfort and a lower heating bill. It still has to be properly sized and routed — which is exactly the subject of this project.
We installed a GREE FREE MATCH R32 system in a 4-head configuration: a single outdoor unit, four wall-mounted air conditioners distributed throughout the house, and not a single metre of ductwork to build.
What we found during the technical visit
The house had the area's classic profile:
- A preserved exposed brick wall in the living area, beautiful to look at and impossible to drill into without taking precautions.
- No existing air distribution. Complete room-by-room baseboard heating.
- An open-plan living and dining area, plus three enclosed rooms upstairs and on the ground floor.
- Significant temperature differences between rooms in winter, and nothing but two window air conditioners in summer.
- An electrical panel with available space, but an owner reluctant to run four new circuits through old walls.
This last point influenced part of the solution, and we will return to it.
The selected system: GREE FREE MATCH R32, GWHD(36)ND6MO outdoor unit
The outdoor unit
- Model: GWHD(36)ND6MO, accommodating 2 to 4 indoor units — the exact limit for a four-head configuration.
- Rated cooling capacity: 36,000 BTU/h, modulating from 8,870 to 40,900 BTU/h.
- Rated heating capacity: 36,000 BTU/h, modulating from 8,870 to 51,180 BTU/h.
- SEER 2 of 21, HSPF 2 of 10, EER 2 of 12, COP of 3.56.
- Heating range: −30 °C to 24 °C. Cooling range: −30 °C to 48 °C.
- 208/230 V power supply, 30 A MCA, 45 A maximum protection.
- Refrigerant R32, factory charge of 2,700 g.
- Dimensions: 1,020 × 826 × 427 mm, 78.5 kg net.
- G10 inverter technology, intelligent defrosting, automatic voltage adaptation, self-diagnostics.
- A2L leak detection sensor included.
- ENERGY STAR certification.
The distribution of the four heads
The zone-by-zone sizing was determined as follows, based on a load calculation rather than a rule of thumb based on square footage:
| Zone | Nominal capacity |
|---|---|
| Living room–dining room (open-plan area, brick wall) | 12,000 BTU/h |
| Primary bedroom | 9,000 BTU/h |
| Second bedroom | 9,000 BTU/h |
| Office | 9,000 BTU/h |
Total connected nominal capacity: 39,000 BTU/h on a 36,000 BTU/h outdoor unit.
The diversity factor: the calculation most quotes skip
This 108% ratio is not a mistake; it is a decision. In a multi-zone system, the combined capacity of the heads almost always exceeds the outdoor unit's capacity because the four rooms never reach their maximum load at the same time. An unoccupied bedroom at 2 p.m. and a sun-filled office at 3 p.m. do not draw power simultaneously.
The risk is going too far in either direction:
- A ratio that is too high (above approximately 130%) produces a system unable to meet the needs of all zones during a simultaneous peak—typically a heat-wave evening when everyone is home.
- A ratio that is too low, with oversized heads for their rooms, creates short cycles, poor dehumidification in summer, and constant discomfort.
At 108%, we remain in a range where the outdoor unit serves all the heads simultaneously during peaks while retaining its ability to modulate very low—down to 8,870 BTU/h—during the long periods of partial load that account for most of the season in Montérégie.
A single electrical circuit for the entire system
That was the argument that resolved the owner's hesitation. With the FREE MATCH R32, the indoor units are powered by the outdoor unit. In practical terms:
- A single dedicated 208/230 V circuit to the outdoor unit, sized according to the 30 A MCA and protected by a maximum 45 A breaker.
- No power circuit needs to be run to each of the four heads.
- A single communication and power cable between the outdoor unit and each indoor unit, routed through the same sleeve as the refrigerant line and drain.
In an older home, where every penetration through lath-and-plaster walls or masonry is a project in itself, this electrical architecture eliminates days of work and finish repairs.
Refrigerant line routing: four runs, one allowance
Four heads mean four separate refrigerant lines converging at the outdoor unit. Each line includes a liquid pipe of 1/4 po and a gas pipe of 3/8 po, insulated independently.
Total length allowance
The GWHD(36)ND6MO allows a maximum total length of 80 m (262 ft), across all branches, and a maximum elevation difference of 25 m (82 ft). This is not a per-head limit: it is an overall envelope to be allocated. In a two-story home with a head in the office opposite the outdoor unit, the allowance is used up quickly. We plot all four routes on the plan before drilling anything, taking into account the detours required by the old structure.
Refrigerant charge adjustment
The unit is precharged for 40 m (131 ft) of piping. Beyond that, R32 must be added at a rate of 0.2 oz per foot (20 g per meter). An installation that exceeds the precharge without a charge adjustment will operate—poorly, and with degrading performance. We measure the actual lengths, calculate the additional charge, and record the value in the service file. This is one of the easiest checks to perform and one of the most frequently omitted.
On this project, the routing required a compromise for the office head: rather than going through the exposed brick wall, we routed around it via an interior partition wall, which lengthened the run by several meters but fully preserved the masonry. The total budget allowed for it—we knew that before we started, not afterward.
Condensate drainage, head by head
This is the number-one cause of service callbacks on multi-zone systems, and it is almost always preventable.
Every wall-mounted air conditioner produces condensate in cooling mode. The drain must descend in a continuous slope from the head to the discharge point, with no reverse slope, sag, or horizontal section. A drain that rises two centimetres along its route accumulates water, develops biofilm, becomes clogged, and the water comes out through the only available exit: the wall, beneath the unit.
Our approach on this project:
- Three gravity-drained heads, with the slope checked with a level along the entire route, the drain integrated into the line set with the refrigerant line.
- One head equipped with a condensate pump, because its position allowed no usable slope toward the outdoors. A correctly installed pump is a legitimate solution; a negative slope that “should work” is not.
- Protected drain outlet outdoors, positioned to prevent the water from freezing into a block against the siding during the first thaw followed by a freeze.
The outdoor unit and winter in the Richelieu Valley
A heat pump that heats down to −30 °C produces defrost water all winter. This water must be able to drain away. The points we apply systematically:
- Elevated support above the expected maximum snow level, with unobstructed clearance beneath the unit for drainage and airflow.
- Vibration isolators between the unit and its support.
- Positioning outside the drop line of a roof slope. A sheet of ice falling two stories onto a heat exchanger settles the warranty question once and for all.
- Clearances are maintained at the rear and on the sides to prevent recirculation of the discharged cold air.
The FREE MATCH R32 intelligent defrost adjusts the cycles according to actual conditions rather than a fixed timer, reducing the number of unnecessary cycles—and therefore the amount of water produced and heat brought back into the house.
R32 and leak detection
The R32 is a low-global-warming-potential refrigerant, classified as A2L and therefore slightly flammable. Three practical consequences:
- The minimum floor area of each room must be validated based on the system’s refrigerant charge. For a multi-zone system with a 2,700 g factory charge plus the additional charge, this calculation is done before selecting the head locations, not after installation.
- The leak detection sensor is included with these systems and must be connected and tested during commissioning.
- The service tools, vacuum pump, and recovery procedure must be A2L-compatible. A technician who treats an R32 system like an older R410A system is taking a risk that is not theirs to take.
Commissioning and balancing the four zones
Deep evacuation of the entire system, with a standing vacuum test before opening the valves. On a multizone system, this step takes longer than on a single-zone system because the vacuum must reach all four branches—and this is precisely the step that rushed installations shorten.
Verification of the simultaneous operation of all four indoor units in heating and then cooling mode, measurement of the discharge temperatures at each unit, checking the current draw, and recording baseline parameters.
Then comes the step we consider part of the installation, not the service: explaining to the homeowner that each indoor unit serves the room where it is located, whether the doors are open or closed. An indoor unit in the living room will not heat a bedroom whose door is closed. Having this conversation during commissioning prevents half of the reported dissatisfaction with multizone systems.
Mistakes that ruin a multizone heat pump
Choosing indoor units by room rather than by load
A 100 sq. ft. bedroom does not need 12,000 BTU/h. An oversized indoor unit in a small enclosed room short-cycles, does not dehumidify, and becomes noisy with every restart. The comfort of a multizone system is determined indoor unit by indoor unit.
Ignoring the diversity ratio
Adding four 12,000 BTU/h indoor units to a 36,000 BTU/h unit results in a 133% ratio. The system will operate most of the time and disappoint precisely on the days when the customer cares most.
Skipping the refrigerant top-up
Beyond the factory charge, the refrigerant charge must be adjusted according to the actual line length. Without this adjustment, capacity drops and the compressor operates under conditions it does not like.
Treating the drain as an afterthought
A continuous slope or a pump. There is no acceptable third option above a finished floor.
Positioning the indoor units based on aesthetics alone
The placement of a wall-mounted air conditioner must take into account air distribution, obstacles, ceiling height, the drain route, and the refrigerant line route. Appearance matters, but it comes after these constraints—and a good installer can almost always find a position that satisfies both.
What to check regarding rebates
Hydro-Québec's LogisVert heat pump component covers air-to-air systems, including multi-zone configurations, for replacing a heating system in an existing residential building connected to the grid. Three checks to make before purchasing rather than afterward: confirming that the exact model appears on Hydro-Québec's list of eligible equipment, verifying the ENERGY STAR certification required for installations completed after November 26, 2025—the FREE MATCH R32 is certified—and confirming that the contractor is enrolled in the program in addition to holding an RBQ licence. The Rénoclimat program may be combined with it, with an energy assessment before and after the work. Chauffez vert does not apply to a home heated with electricity.
The amounts and criteria change periodically. We verify eligibility for the project before finalizing a quote rather than providing a figure that may not materialize.
The result
The system was commissioned in the spring and operated in cooling mode throughout the summer. The two observations reported by the homeowners are consistent with what we regularly see with this type of conversion: the elimination of temperature differences between rooms and the ability to regulate the temperature in the office without heating or cooling the entire house. The brick wall remains intact. A follow-up visit is scheduled after the first sustained period of cold weather to assess the performance of the four zones below −20 °C and adjust the settings.
AirGreen in the Richelieu Valley and throughout the surrounding area
We install multi-zone heat pumps, wall-mounted air conditioners, central systems, and heating solutions in Saint-Jean-Baptiste, Mont-Saint-Hilaire, Beloeil, McMasterville, Otterburn Park, Saint-Basile-le-Grand, Chambly, and Longueuil, as well as in Montreal, Laval, on the North Shore, and throughout the South Shore. Every HVAC installation project begins with a room-by-room load calculation and a complete layout of the refrigerant and drainage lines—before the first hole is drilled.
For an on-site assessment in Saint-Jean-Baptiste or elsewhere in Montérégie, contact us.