The hole in the wall next to the head is not an oversight
In the photo of this Saint-Lambert installation, the GREE FreeMatch R32 wall-mounted heat pump is installed, level, and connected. To its right, at the same height, a rectangle has been cut into the drywall. The wood framing, some insulation, the two white refrigerant lines, and the black interconnection cable plunging into the wall cavity are visible.
This rectangle is the part of the work that almost no quote names and no competitor article shows. It is not a sign of a poorly executed job: it is the trade-off of a concealed route. The Saint-Lambert client did not want any conduit in the room. That decision, made at the quoting stage, is paid for with openings in the wall—and the real question is not whether openings will be made, but how many, where, and who will close them.
That is the subject of this article. It does not appear elsewhere on our site, and it should be read before signing, not afterward.
A concealed route does not require one opening: it requires several
The homeowner’s assumption is almost always the same: drill behind the head, go down through the wall, and come out outside. In a new house with the walls open, that is true—and it is the best time to install, as explained in our Dundee article. In a finished house, it is false, for three mechanical reasons.
- The line set does not bend like an electrical wire. An electrician pulls a flexible cable twenty feet through a cavity using a fish rod. A refrigerant line set consists of two insulated copper tubes, a drain, and a cable assembled into a bundle. This bundle has a minimum bend radius: bend it too tightly, and the copper becomes oval, reducing the usable cross-section. You do not “fish” it; you guide it—and you guide it from a point where your hand can enter.
- A wall cavity is not an empty tube. There are nailing surfaces and horizontal fire blocks, often halfway up, that close off the cavity across its width. Each requires either blind drilling — which we do not do — or one more opening, right there. In addition, in a Saint-Lambert home, where more than 55% of the housing stock consists of single-family homes often modified over the decades, there may be plumbing stacks, added circuits, and ducts from an older system.
- The drain, however, is not allowed to rise. The condensate pipe must maintain a continuous slope along its entire route. The shortest path is rarely the one that preserves the slope: it is often a longer route, with one or two additional openings to check the fall before closing up.
The contents of a cavity and the probing method — the inspection opening made before any drilling, the list of what we look for, and the decisive rule that the two lines remain continuously isolated even inside a heated wall, because the suction line condenses inside the cavity — belong to our Saint-Étienne-de-Beauharnois article, and we are not rewriting them here. What this page adds is what comes afterward: the series of openings required by the geometry, and what we do with them.
What we do before cutting anything
- The route is marked with tape on the wall, from the back of the head to the exterior outlet, and the client sees it before the saw comes out of the truck.
- Opening points are marked separately, with the reason written beside them in pencil: “blocking,” “column,” “change of direction.”
- The cuts are made cleanly and rectangularly, aligned with the studs whenever possible. A torn cut costs three times more to close up than a straight cut.
- The cut pieces of drywall are kept. Replacing an original piece in its place creates a thinner joint and a flatter finish than fitting in a new piece.
- Every pan and drain is water-tested before closing up, never afterward.
What gets closed up, and what intentionally remains accessible
Not every opening is closed up. The decision is made opening by opening, and it deserves to be explained to the client because it has consequences for the next twenty years.
- An opening made to pass through — used solely to route the bundle — is closed up. There is nothing behind it that will need to be revisited.
- An opening located at a connection, a sharp change in direction, or a low point in the drain deserves an access panel rather than an invisible joint. The reasoning behind the access panel and the obligation to record its location in the project file belong to our Terrasse-Vaudreuil article, which discusses the closet used as a technical route—and the closet visible in this photo, beneath the head, is exactly that type of route. We refer you there rather than repeating it here.
- An opening that passes through a fire separation must be closed, and sealing it is work in its own right, not a bead of sealant run over it with a finger. The position we take on this type of penetration—sealing across the entire thickness, and having compliance validated with a building professional or the municipality rather than inferred by an installer—is the position set out in our Longueuil article, which addresses the shared wall between a garage and the dwelling.
The rule we apply is simple to state: a conduit buried in a finished wall can no longer be inspected with a screwdriver. That is the price of aesthetics, and it is justified—but it must be chosen knowingly. Our Saint-Louis-de-Gonzague article argues the opposite case, that of a surface raceway, in a house where the wall offered no usable cavity. Both approaches are valid; what is not valid is being subjected to one while believing you chose the other.
Who closes it up, who sands, who paints: the actual scope of the work
This is the point that causes the most misunderstandings at the end of a project, across all types of contractors. Let us be clear.
Interior finishing is not included in the HVAC scope of work. This is an industry rule, and ours as well—it is explained in our Saint-Bernard-de-Lacolle article. But our Vimont article adds the nuance that changes everything, and we are reiterating it here because it is central to this project: an honest quote does not necessarily include finishing, but it does NAME it. The work exists. Someone will pay for it. The only unacceptable scenario is for the client to find out on the day the team packs up its tools.
Specifically, here is how the visible work in the photo is divided:
| Work | Who | When |
|---|---|---|
| Cutting the openings, routing the harness, sealing the penetrations | Us | Installation day |
| Replacing the pieces of drywall, screwing them into the backing | Us, unless otherwise agreed | Installation day |
| Joint tape, compound, sanding, primer | Drywall finisher | Afterward, over several days |
| Finish paint | Painter or homeowner | Lastly |
The actual repair schedule is what homeowners underestimate the most. A properly finished drywall joint requires two to three coats of compound, each dried before the next, with sanding between coats. It is not a day’s work; it is a week on the calendar for a few hours of labour. And the result must be assessed under raking light: a wall lit from an angle reveals every repair, which means you have to feather the finish out much wider than the cutout itself. Our Dorval article addresses this phenomenon specifically.
Two practical consequences:
- Gypsum dust and a new unit do not mix. Sanding produces fine dust that settles everywhere and sticks to the coil of a running unit. If joint compound work follows the installation, the unit must remain switched off and protected during dusty work — the order of the trades is explained in our Beauharnois article.
- Painting must come afterward, never beforehand and never while the unit is running.
The final handover: what to check before signing
There is a difference, and it is immense, between “the unit works” and “the work is complete”. The first finding can be made in thirty seconds with a remote control. The second is a procedure. The second is what protects the customer, and it is the one nobody explains to them.
Why a quick demonstration proves almost nothing
A unit blowing cold air on the day of installation proves that the circuit contains refrigerant and that the fan is running. It does not prove that the system was evacuated properly, that the charge was weighed rather than estimated, that the drain maintains its slope under continuous load, that both zones operate simultaneously without interfering with each other, or that heating mode starts — which, in August, cannot in any case be verified under real conditions.
That is why a serious final handover relies on written readings, not on an impression.
What must be recorded and given to the customer
The handover file is the only lasting proof of the quality of the work. Its contents — serial numbers for each unit, the AHRI code for the installed combination, actual developed lengths, weighed refrigerant quantity, commissioning readings, proof of evacuation, and RBQ licence — are detailed in our Montréal-Est article, while our Villeray article covers warranty registration and handover photos. Our Pierrefonds-Roxboro article adds the line that truly protects the customer: what was observed but not corrected, written down in black and white.
On a project like the one in Saint-Lambert, two additional entries are essential, and they follow directly from the concealed routing:
- The location of every opening made, whether closed up or not, with a photo taken before closure. Fifteen years from now, the plumber who opens this wall will know what is behind it.
- The locations of the retained access panels, including what they provide access to.
The deficiency list: dated, assigned, and given deadlines
An honest end-of-project acceptance rarely produces a blank page. It produces a deficiency list, and a properly recorded deficiency is infinitely better than a forgotten one. Three requirements for it to be useful:
- Each item is described precisely—“30 × 30 cm opening to the right of the indoor unit, drywall put back in place, joints not finished,” not “finish the wall.”
- Each item has a named party responsible: us, another trade, or the homeowner.
- Each item has a date or completion condition. “At the fall return visit” is an acceptable date if the fall return visit itself is scheduled.
This final point refers to a principle we apply elsewhere in the series: summer commissioning validates only half of the system, and heating-related checks should be explicitly scheduled rather than overlooked—as discussed in our article on Bois-des-Filion.
Seven checks to complete with the installer before they leave
- Run both zones at the same time in cooling mode and listen.
- Pour water into each drain pan and watch it flow outside.
- Open the front panel of each indoor unit all the way to confirm that the filters will be accessible once the wall has been refinished.
- Ask for the amount of refrigerant added and the basis on which it was calculated.
- Have every opening made in the wall identified and confirm in writing what remains to be done and by whom.
- Photograph the outdoor nameplate and the inside of the wall yourself before closing it up.
- Have the return-visit date and what it will verify recorded.
The technical choice: GWHD(30)ND6MO, 15,000 + 9,000 BTU/h
Two zones: the open-concept ground floor and the primary bedroom upstairs, separated by a route that runs inside a wall and a closet pathway. The rest of the house retains its electric baseboard heaters.
| Data (GREE X610068B brochure) | GWHD(30)ND6MO |
|---|---|
| Connectable indoor units | 2 to 4 |
| Nominal cooling capacity | 8,300 W — 28,400 BTU/h (modulating 8,190–34,100) |
| Nominal heating capacity | 8,800 W — 30,000 BTU/h (modulating 8,190–40,900) |
| Efficiency | SEER2 21 · HSPF2 10 · EER2 12.5 · EER 4.00 · COP 4.19 |
| Operating ranges | Cooling −30 to 48 °C · Heating −30 to 24 °C |
| Electrical | 208/230 V · MCA 23 A · MOCP 35 A |
| Refrigerant | R32, 2,200 g · 40 m factory charge · 20 g/m additional charge |
| Maximum total length | 80 m · 25 m elevation difference |
| Certification | ENERGY STAR · AHRI 214931588 (not ducted) |
Why this model, and why the argument here is a routing argument. The heads' 24,000 BTU/h represent 85% of the nominal cooling capacity and 80% of the heating capacity: a comfortable ratio, with no acrobatics. But capacity was not the deciding factor; length was.
The developed length of a concealed route is not the length measured on the plan. A route that goes around an obstruction, shifts over two cavities to avoid a plumbing column, or takes a diagonal through a floor to maintain the drain slope can easily add three to six metres to the estimate made with a tape measure. On this job, the initial estimate was approximately 16 m; the actual routes total 22 m developed (9 m and 13 m).
This difference has no impact on the GWHD(30), whose factory charge covers 40 m and whose maximum total allowable length is 80 m: no refrigerant was added, so there is no effect on the minimum room area required by the A2L rating plate—a topic covered in Sainte-Anne-de-Bellevue and Dundee. On a model whose factory charge ends at 10 m, the same routing surprise would have meant a weighed top-up and an additional verification. On a job where the routing is uncertain, buying extra length margin costs less than discovering you need it. Managing total length as a shared budget among the zones is covered in our Oka article; the elevation difference, which does not track capacity, is addressed in Sainte-Thérèse.
Two candid details about this model that we do not rewrite: it is the most efficient in the lineup (EER 4.00 / COP 4.19), an argument developed in Pierrefonds-Roxboro, and the only one whose nominal capacities differ between the two modes, as explained in our Outremont article. It can also accommodate up to four heads: two ports remain available for an additional bedroom or basement, without changing the compressor.
Head above the cabinet opening
The position visible in the photo—head high, tucked tightly beneath the ceiling, just above a closet opening—is not an aesthetic choice. It results from the strip of wall available once the room's bed, window, and door have been positioned. Everything concerning this position—why the head ends up there, why a closet header is not a structural header, why the plate must be screwed into actual wood rather than drywall, and the conflict between the folding-door hardware and the anchoring line—is explained in detail in our Terrasse-Vaudreuil article. We apply it here without repeating it.
Saint-Lambert: a small, dense, historic city that became autonomous again
Saint-Lambert covers 7.56 km² on the South Shore, opposite Jean-Drapeau Park, and had 22,761 residents in the 2021 census, an increase of 4.1% over five years—a population density that places it among the most compact municipalities in Montérégie. Its name comes from Lambert Closse, and the area, long a marshy tract known as Mouillepied, developed with the arrival of the railway in the 1850s, followed by the Victoria Bridge in 1859, the oldest link between Montreal and the South Shore. The municipality was established in 1857, became a village in 1892, a town in 1898, and a city in 1921. The Saint-Lambert locks, built in the 1950s, form the easternmost entrance to the St. Lawrence Seaway.
Municipally, Saint-Lambert merged with Longueuil on January 1, 2002; its citizens voted for demerger on June 20, 2004, and the city was reconstituted on January 1, 2006. It is part of the Longueuil agglomeration while having its own bylaws—a distinction our article on Longueuil points out without addressing, and one with a very practical consequence for HVAC: the rules applicable to installing outdoor equipment cannot be inferred from those of the neighboring city. We verify this question with the municipality concerned, on a case-by-case basis.
For an HVAC contractor, Saint-Lambert's defining feature lies elsewhere: more than 55% of the housing stock consists of single-family homes, some of which—particularly the Quebec cottages on Riverside Street—represent more than a century of architectural heritage. An older housing stock renovated in successive layers is exactly the context where the routing costs more than the equipment, and where the article you have just read stops being theoretical.
Our teams serve Saint-Lambert, Longueuil, Brossard, Boucherville, Saint-Bruno-de-Montarville, La Prairie, and the entire South Shore, as well as Montreal, Laval, and the North Shore.
Six mistakes to avoid when installing a concealed line
- Accept a concealed route without seeing where the openings will be. They will exist; the only choice is whether to discover them before or after.
- Drill blindly into a cavity because a stud finder “confirmed” it was empty. A detector identifies a mass, not what it is.
- Close up the wall before testing the drain with water. Reopening a finished wall costs ten times as much as the initial opening.
- Apply joint compound while the unit is running. Drywall dust gets into the coil.
- Throw away the cut drywall pieces. They provide the best possible joint.
- Sign off on a completed project without a deficiency list. Anything not written down that same day no longer exists three weeks later.
Programs, warranty, and maintenance
The GWHD(30)ND6MO is ENERGY STAR certified and bears AHRI code 214931588 in a ductless configuration. Quebec energy-efficiency programs — LogisVert, Rénoclimat — are based on the combination actually installed, not on the outdoor model alone: we confirm eligibility when opening the file, using the combination's code, and we publish neither an amount nor a promise of eligibility. The basic warranty is 10 years, with a possible extension upon product registration and proof of installation.
When it comes to HVAC maintenance, a two-zone system with one line buried in a wall requires particular attention to one point: the drain. A concealed drain that becomes clogged does not announce itself with a drop on the wall; it announces itself with a stain on the ceiling of the floor below, often quite late. Clean the filters every few weeks during the season, run each zone monthly during the off-season, and schedule an annual visit to check drainage.
At AirGreen, we design, install, and maintain wall-mounted heat pump, wall-mounted air conditioner, and central heat pump systems in Saint-Lambert and throughout Greater Montreal. For a concealed-line project, we determine the route, the necessary openings, and the exact scope of work before the final quote, so the wall is never a surprise.