Five heads, five drains: the litre of water per day nobody mentions before signing
When a multi-zone system breaks down, the customer calls. When it leaks, the customer calls the insurance company. That's the difference between a service call and a loss, and with multi-zone wall-mounted heat pumps, the second situation almost always stems from the same place: condensate drainage.
A wall-mounted indoor unit in cooling mode condenses moisture from the air on its coil. This water falls into a drain pan and then flows through a small-diameter pipe, sloped over its length, often for several metres, through a wall or floor. On a single-head installation, it's a minor detail. On the five-head installation we completed in Les Cèdres, in the Vaudreuil-Soulanges RCM, that's five drain pans, five pipes, five slopes to maintain, and five outlet locations to choose — and a single mistake is enough to turn a beautiful project into a claim.
At AirGreen, we install and maintain HVAC systems throughout Montérégie, in Montreal, Laval, and Longueuil, on the North Shore and South Shore, and many of the corrections we make to other contractors' work concern precisely this issue. Here's how we addressed it on this project.
The context: Les Cèdres, between the river and the Soulanges Canal
Les Cèdres covers approximately 89 km² on the north shore of the St. Lawrence River, between Lake Saint-François and Lake Saint-Louis, about fifty kilometres west of Montreal and less than thirty kilometres from the Ontario border. The municipality is crossed from east to west by the Soulanges Canal and its cycling path, bordered by the Les Cèdres rapids, and served by Highway 20 and Highway 30. It retains a strong agricultural character and considerable built heritage while absorbing part of Vaudreuil-Soulanges' residential growth.
It is this dual nature that makes the HVAC sector interesting: it includes everything from 19th-century village homes to single-story or two-story residences built over the past thirty years, often heated with electric baseboard heaters and without any ductwork.
The property in question falls into the second category: a two-storey family home with a fully finished basement, all-electric heating, no ductwork, and cooling previously limited to a portable unit. The client wanted five separate zones, including the basement.
Five zones, five capacities
After the technical visit and room-by-room assessment:
- Open-plan dining area–living room (main floor) : 12,000 BTU/h
- Family room in finished basement : 9,000 BTU/h
- Primary bedroom (upstairs) : 9,000 BTU/h
- Second bedroom (upstairs) : 6,000 BTU/h
- Enclosed office (upstairs) : 6,000 BTU/h
Total indoor capacity: 42,000 BTU/h on a compressor rated at 42,000 BTU/h for cooling, exactly 100%. There is no diversity margin, and that is deliberate: the house retains all of its electric baseboard heaters, the five rooms are never used at the same hours, and a generous cooling ratio becomes a heating bill. The full reasoning was presented in our Saint-Denis-sur-Richelieu article and, for the specific case of five zones, in the Sainte-Martine article.
A word about the 9,000 BTU/h in the basement, because this is an instinct we often have to correct: a finished basement has a significantly lower cooling load than an equivalent room on the main floor. It is surrounded by earth, receives almost no solar gain, and benefits from the thermal inertia of the ground. Installing the same capacity as in the living room results in an oversized unit that short-cycles, fails to dehumidify, and leaves the basement damp—exactly the opposite of the desired result.
Two checks were completed before ordering and are worth naming because they regularly disqualify a zoning plan:
- The basement ceiling height. The nameplate on an indoor R32 unit specifies a minimum installation height—a point we documented in detail in our Dundee article. A 2.1 m basement fails this criterion. This one measured just over 2.5 m, leaving the clearance needed to install the head at the prescribed height.
- The surface area of the smallest room. In an R32 multi-zone system, the smallest room served governs, not the largest. The enclosed office just passed, confirming the choice of a 6,000 BTU/h head rather than a 9,000 one chosen “out of habit.”
The selected outdoor unit
Five zones require the GWHD(42)ND6MO: it is the only unit in the GREE FreeMatch R32 range approved for two to five indoor units. We published the complete connection table and the commercial consequence of this constraint in our Sainte-Martine article.
The values used for the information presented here: SEER2 21, HSPF2 10, EER2 12, COP 3.9, code AHRI 214931590 in ductless configuration (214931596 in ducted configuration, 214931600 in mixed configuration), heating operation down to -30 °C with modulation reaching 54,590 BTU/h, MCA 30 A and maximum protection of 45 A on a single dedicated circuit since the indoor units are powered by the outdoor unit, 2,700 g of R32 factory charge, integrated A2L leak detector, intelligent defrost, automatic voltage adaptation, and a mass of 79 kg for 1,020 × 826 × 427 mm. The unit is certified ENERGY STAR according to the manufacturer's specifications.
Five drain pans, five hoses: the calculation we make before drilling
In the height of July humidity, a wall-mounted head operating several hours a day produces roughly one to a few litres of water daily, depending on the humidity level, operating time, and room size. Multiplied across five zones, that is a volume that is far from symbolic—and it must leave the house by gravity, never flowing back uphill.
The rule is simple to state and difficult to maintain over five runs: a continuous, downward slope over the entire length, without a single low point. A hose that sags two centimetres in the middle of a six-metre run creates a reservoir of stagnant water. In three summers, this reservoir becomes a biological blockage, the drain pan overflows, and water appears on the wall beneath the unit—often long after the installer has left.
What we systematically check:
- Support spacing. A poorly supported flexible hose creates its own low point between two attachments.
- The slope checked along the entire length, not just at the beginning and end.
- The absence of a backfall at the wall penetration, where it occurs most often because the outlet is aligned with the façade's aesthetics rather than with drainage.
- Continuous insulation of the suction line, because a poorly insulated line also condenses and adds its water to that from the pan. We developed this mechanism in our Saint-Étienne-de-Beauharnois and Saint-Louis-de-Gonzague articles.
Why we never combine five drains into one common pipe
It is an obvious cost-saving measure on a five-zone installation: instead of five penetrations and five outlets, the drains are gathered into a manifold and routed outside only once. We refuse to do this, and here are the reasons, in the order in which they eventually become apparent.
A single blockage puts five zones out of service. An individual drain that clogs causes one pan to overflow. A clogged manifold sends water back toward the lowest pan in the network—that is, into a room that did nothing wrong and, most of the time, is not the one anyone suspects.
Diagnosis becomes impossible. When five zones share one line, it is no longer possible to determine where the water is coming from without disassembling the system. With five separate drains, we look at the five outlets: the one that is not flowing in the middle of a heat wave is the one with a problem. It is a thirty-second diagnosis, performed from outside.
The pans are connected. Each pan is open to the air in its room. Connecting the drains creates an air path between zones: gurgling noises when one head starts, odors transferring from one room to another, and loss of drainage flow.
A pumped line must never be connected to a gravity line. This is the most damaging—and most common—configuration we find in corrective work. A pump pushes; if its line joins a gravity drain, it also pushes upstream and fills the neighboring head's pan.
The exception: the basement and its condensate pump
The basement head had no possible gravity drain: its outlet would have been below ground level. It therefore received its own condensate pump, independent of the other four drains, with a safety float switch wired to shut down that head in the event of pump failure—so a pump problem results in a zone that stops cooling, never water on a finished floor. We described this setup in our Saint-Michel article, in a condominium context where the risk of water damage is even greater.
Two details specific to a finished basement: the pump must remain accessible for maintenance after finishing, and it makes an intermittent noise that should be located away from a sofa or bed. In the other four areas, we retained gravity drainage—it is always the first choice, because a pump is one more mechanical component in a system that already has enough. Incidentally, the side through which the drain exits the unit is decided before securing the mounting plate, based on the line routing; we illustrated this point in our Coteaux article, in the same RCM.
Where the drain empties outside, and what happens in January
The outlet point is treated as a decision, not as a consequence of drilling.
- Never above a sidewalk, staircase, or entrance. Water that flows in September freezes in October. This is a safety issue before it is an aesthetic one.
- Never directly against the siding or foundation. A constant trickle of water stains the siding, saturates the soil at the base of the wall, and eventually ends up where no one wants it.
- A bed of stone or a drip well beneath each outlet, so the water flows into the ground instead of eroding it.
- Never near the outdoor unit. This is the detail almost no one anticipates: water from indoor drains that empties near the outdoor unit mixes with its defrost water and contributes to the formation of the ice column beneath its chassis.
Let’s clarify something homeowners often confuse: in winter, it is not the indoor drains that produce water; it is the outdoor unit. In heating mode, the outdoor coil frosts over and then defrosts, and this water must be able to leave the unit’s base. The indoor drains, meanwhile, operate only in cooling mode. Confusing the two leads you to look for a problem where none exists.
The water test before closing everything up
Each pan is filled with water and checked at the outlet before a single wall is closed up and before the first startup. A reversed slope found at this stage costs twenty minutes; found during the first heat wave, it costs a basement ceiling.
The outdoor unit under a pitched roof: what winter decides for you
Snow and ice sliding off the roof
The outdoor unit’s location is chosen by looking up first. A 79 kg appliance placed beneath a roof slope, in a roof valley, or under an overhang without a snow guard will sooner or later be hit by a slab of compacted snow or ice at full speed.
What this causes: a dented fan grille, a cracked blade that throws the motor out of balance, crushed heat-exchanger fins over part of the surface—meaning a permanent loss of capacity that triggers no error code—and, in serious cases, stress on the connections to the service valves, that is, a slow leak from R32.
Our order of preference, on this project as elsewhere:
- Move the unit out of the path. It is free at the design stage and impossible afterward.
- Have snow guards installed on the roof. That falls to the roofer, not the HVAC contractor, but we are the ones who must flag it before the problem exists.
- Build a wall-mounted shelter as a last resort and only if it meets the conditions below.
A poorly designed shelter does more damage than no shelter at all
The condenser shelter is probably the most poorly executed accessory in the industry. The three mistakes we see most often:
- A shelter that is too low. Air blown by the fan exits through the top. A panel installed a few centimetres above the top sends that air straight back into the heat exchanger: the unit draws in its own air again, capacity drops, and in heating mode, defrost cycles multiply. This is recirculation, and it is the best way to make a high-performance system disappointing.
- A shelter enclosed on the sides. A condenser draws air in through its sides and rear. Covering them to “protect” the unit is like plugging its nostrils.
- A shelter that rests on the unit. It transmits its vibrations to the structure and blocks access to the service panel. A shelter must be attached to the wall or floor, never to the condenser.
The basic rule: the shelter must respect the clearances specified in the installation manual—above, behind, and on the sides—and these values vary from one model to another. No sales sheet can replace them.
Other details of a condenser that makes it through the winter
- An elevated base, sized for local accumulation rather than a generic standard.
- A drainage bed beneath the unit, so defrost water drains away instead of freezing under the chassis.
- The disconnect switch and junction box above the snow level.
- Nothing stored around it. A shed, trailer, or pile of firewood placed within one metre of the unit has the same effect as an enclosed shelter.
- Clear access in February. A technician must be able to reach the service valves in the dead of winter, not just in June.
What a five-zone installation day really looks like
It is a question we are rarely asked and should be asked more often, because a quote promising a five-zone installation in one day should give you pause.
For this type of project, allow two working days, sometimes more depending on the complexity of the runs. The sequence: positioning and fastening the five mounting plates, drilling and installing sleeves, setting up the outdoor unit and its base, running the five line sets and five interconnection cables with port identification, making connections and performing leak tests, deep vacuum with decay test, weighed charge adjustment according to the actual measured line length, then commissioning one head at a time, in both modes, with a physical check that the discharged air is indeed coming out into the correct room.
What we ask the client to prepare: approximately two metres of clearance in front of each head location, unobstructed access to the electrical panel, a parking space near the outdoor unit location, and pets kept away from doors that will remain open.
The dining-room head
In the room shown in the photo, the 12,000 BTU/h head is installed very high, tight beneath the ceiling, on a furnished and decorated dining-room wall: pendant light, curtain rod, and wall clock. The display reads 61, in degrees Fahrenheit—a commissioning setpoint, not an operating setpoint; we explain why in our Saint-Édouard article.
Three constraints were checked before drilling, and each is covered in full elsewhere in this series: the pendant light located within the first few metres of the airflow that changes its path (see our Sainte-Martine article), the side clearance to ensure that a drawn curtain cannot be sucked toward the return-air grille (see Ormstown), and the ceiling clearances required by the indoor unit’s manual (see Verchères).
A usage point specific to a dining room: no one sits two metres from a bedroom head, but everyone sits beneath a dining-room one. In air conditioning, directing the louvers forward rather than downward prevents air from blowing directly onto diners—this is the leading cause of service calls that are not actually service issues.
Mistakes to avoid
- Accepting a common manifold for several condensate drains. Saving a few hours is paid for once, in water damage.
- Connecting a condensate pump outlet to a gravity-drain line.
- Placing the outdoor unit without looking at the roof above.
- Enclosing the sides of a condenser shelter.
- Not testing every drain pan with water before closing the walls.
- Having five zones priced without a technical visit, when the basement height and the size of the smallest room could invalidate the design.
- Forgetting to register the warranty: 10 years of standard coverage, extended to 12 years upon registration with the distributor and proof of installation.
Rebates, warranty, and documentation
The GWHD(42)ND6MO is listed as eligible for local rebates on the manufacturer's product sheet. For an electrically heated home in Vaudreuil-Soulanges, Hydro-Québec's energy-efficiency programs (LogisVert) and Rénoclimat generally apply; Chauffez vert, which is intended to replace fossil-fuel heating, does not apply. The criteria and amounts change from year to year, and the declared AHRI number must match the combination actually installed—an application may be denied for this reason alone.
At the end of the project, we provide the serial number of each head unit associated with its room, the measured length of each line, the amount of refrigerant added and weighed, the port-by-port assignment, commissioning readings, the dedicated circuit number, the route and exit point of each of the five drains, and the date the warranty was registered. This last item is missing from almost every commissioning file—and it is precisely the one people look for when a water stain appears on a ceiling.
At AirGreen, we design, install, and maintain multi-zone wall-mounted heat pump, air conditioning, and heating systems in Les Cèdres, Coteau-du-Lac, Vaudreuil-Dorion, Saint-Lazare, and throughout the Vaudreuil-Soulanges RCM, as well as in Montreal, Laval, Longueuil, on the North Shore, and on the South Shore.
AirGreen — RBQ 5645-9605-01 — (514) 316-2973 — sales@airgreen.ca