Installation of a GREE FreeMatch R32 two-head wall-mounted heat pump (GWHD(24)ND6MO) in the Montréal-Nord borough

The ceiling-mounted smoke detector determines where the head can go

In the photograph of this project, the most important element is not the unit. It is the small white box mounted on the ceiling, a few feet from the wall-mounted head: a smoke detector.

In roughly fifty GREE FreeMatch R32 projects documented this year, we have written about ceiling drops, mouldings, pendant lights, barn-door tracks and sprinkler heads. Never about the smoke detector, even though it is on the ceiling of nearly every room where we install, is a life-safety device, and the airflow from a wall-mounted heat pump interacts directly with it.

This interaction works both ways, and neither device indicates it with a useful alarm. This is exactly the kind of detail that distinguishes a contractor who looks at the ceiling before drilling from one who does not.

At AirGreen, we carry out HVAC installations throughout Montréal, Laval, Longueuil, the North Shore and the South Shore. Here is how we address this issue, and what this Montréal-Nord project required in addition.

The Montréal-Nord project at a glance

The borough of Montréal-Nord has 84,234 residents across just 11.1 km², or approximately 7,623 inhabitants per square kilometre. After Côte-des-Neiges–Notre-Dame-de-Grâce, it has the highest density of all the boroughs where we documented a project this year—nearly ten times that of L'Île-Bizard–Sainte-Geneviève. Bordered along its entire length by the Rivière des Prairies, the borough has 21 parks, six splash pads, two community gardens, notable built heritage along Gouin Boulevard, and the monumental work La vélocité des lieux by the BGL collective.

This density and this type of building—many duplexes, triplexes and low-rise buildings from the 1950s to the 1970s, with low ceilings and compartmentalized rooms—explain the configuration selected:

• Outdoor unit: GREE FreeMatch R32 GWHD(24)ND6MO
• Head 1: 9,000 BTU/h wall-mounted unit, open-concept living–dining area
• Head 2: 6,000 BTU/h wall-mounted unit, primary bedroom
• Installed indoor capacity: 15,000 BTU/h, or 63% of nominal capacity
• AHRI codes: 214931587 (non-ducted), 214931593 (ducted), 214931597 (mixed)
• Developed lengths: approximately 11 m and 14 m, for 25 m total, within the 30 m precharged

The choice of model and two-zone sizing are not the subject of this article, and we will not revisit them: the comparison between the small and large unit is covered in our Beaconsfield article, the reading of the minimum and maximum capacity line in the Dorval article, the rule that a single head should never equal the entire compressor in the Kirkland article, the pipe-run length as a criterion in the Dollard-des-Ormeaux article, and the distinction between precharge and absolute limit in the Côte-des-Neiges–Notre-Dame-de-Grâce article. What this article is about is the ceiling.

Two opposing effects, with no alarm to signal them

A smoke detector works because smoke reaches it and enters its detection chamber. Anything that changes the movement of air around it changes this condition. A wall-mounted head continuously moves air in a thin layer along the ceiling for months each year.

Moving air can delay detection

The airflow from a wall-mounted heat pump follows the ceiling for several metres. A detector located in this stream is swept by a clean, fast-moving current of air. Two consequences combine: the smoke plume, which naturally rises and spreads beneath the ceiling, is diluted and diverted before reaching the device; and the constant airflow may prevent the smoke from lingering around the detection chamber long enough to enter it in sufficient quantity.

This is not a theory: it is why detector manufacturers' installation instructions prescribe a minimum distance from air outlets, ceiling fans, and anything else that circulates air. We do not publish a figure here because this distance varies by detector model and by the authority having jurisdiction: it is specified in the instructions for the installed detector and must be confirmed with the fire department, not in a blog post.

The key point is simpler. The detector was installed in a room that did not have a heat pump. Installing a head changes the conditions in which it was positioned, and it is up to the HVAC contractor to point this out.

Dust carried by the airflow fouls the detection chamber

The second effect is slower and more common. The blown air carries fine dust, and a detector placed in this airflow receives much more of it than a detector located in a calm corner.

A detection chamber loaded with dust does not stop working: it becomes too sensitive. The result is a nuisance alarm, usually at night, with no smoke and no visible cause—and the human response to a repeated nuisance alarm is always the same: remove the battery. A detector fouled by the jet from a heat pump therefore often ends up as a disabled detector, which is the most serious consequence of this entire chapter.

The same mechanism shortens the device's service life. A detector has a limited lifespan indicated on its housing; placed in a dust-laden airflow, it reaches the end of that lifespan sooner.

What we check before choosing the mounting point

The method consists of five steps, all carried out during the technical survey, before a hole is drilled.

1. Look at the entire ceiling. Smoke detectors, carbon monoxide detectors, combination detectors, and sensors connected to a centralized alarm system. In a multi-unit building, some of these devices are interconnected and cannot be moved freely.
2. Position the head in relation to the axis of the airflow, not just in relation to the wall. A detector behind the head is in a calm zone; the same detector a few metres in front, in the airflow path, is directly in the draft.
3. Consult the instructions for the detector concerned rather than applying a general rule from memory.
4. If the ideal position of the head conflicts with the detector, move the detector, not the other way around—and not us. A detector connected to an alarm system or an interconnected network is the responsibility of the electrical contractor or building manager. A standalone battery-powered detector is easy to move, but the decision and the new position must be recorded in the file.
5. Never resolve the conflict by aiming elsewhere. Pointing the airflow away from the detector may seem sufficient, but the louvers can be adjusted, knocked out of alignment, and changed seasonally; the physical position does not change.

During the work: protect it, then put it back into service

Drilling into a wall produces fine gypsum and plaster dust that rises and spreads beneath the ceiling. A detector left uncovered during HVAC work receives a concentrated dose, and that is precisely what causes nuisance alarms in the following weeks.

Our practice, and what a client is entitled to expect from any contractor:

• The detector is protected during the dusty phase, with a detector cover or a bag, never with adhesive tape stuck over the openings.
• The protective cover is removed the same day, before the crew leaves, and is never left “for the next visit.”
• The detector is tested using the test button at the end of the project, in the client's presence, and the action is recorded in the project completion document.
• If the detector is visibly at the end of its service life—the date on the casing has passed, the casing is yellowed, or there is a low-battery warning—we report it in writing. Replacing it is not our mandate, but reporting it is our responsibility.

One final point that follows from the same reasoning: in a room containing a combustion appliance, a carbon monoxide detector has its own placement requirements, different from those of a smoke detector. They should be verified with the detector manufacturer, not inferred by analogy.

The outdoor unit's A2L detector is not a smoke detector

A confusion regularly arises at the end of a project, and it is worth clearing it up.

The outdoor units in this range incorporate an A2L leak detector associated with the R32 refrigerant, which is mildly flammable. This is a genuine safety device and is one of the reasons this generation of equipment is safer than the previous one. But it monitors one thing only: the abnormal presence of refrigerant around the unit.

It does not detect smoke. It does not detect carbon monoxide. It does not protect the property. It does not replace any detector required in a residence, and having a new heat pump does not change a landlord's or tenant's obligations regarding smoke detectors. We say this at commissioning because it is better to say it twice than not often enough.

Data for the installed unit

The complete technical table for the GWHD(24)ND6MO was published in our Dorval article. Here are the relevant lines for this page.

An integrated A2L leak detector, G10 inverter, intelligent defrosting, automatic voltage adaptation, and self-diagnostics are standard across the entire range. Circuit load calculations are the responsibility of a master electrician; our contribution is the manufacturer's data.

Install a heat pump in a rental property

Montréal-Nord is a borough of plexes and multi-unit buildings. The question we are asked most often here is not technical: it is “am I allowed to?” It comes from tenants who want comfort, owner-occupants of duplexes who want to equip their floor without setting a precedent for their tenant, and building owners who receive three requests in July.

Let's be clear from the outset: we are not lawyers and do not provide legal advice. Relations between landlords and tenants are governed by the lease and the law and, in the event of a dispute, by the Administrative Housing Tribunal. What we can describe is what a well-prepared file contains and how the answers to these questions concretely affect the work on site.

Questions to settle before the quote, not afterward

We refuse to open a wall until these four points are in writing:

1. Who authorizes it. The building owner's written authorization must be on file before the order, just like a layout survey. In a divided co-ownership, it is the syndicate that authorizes the use of common areas, including a balcony or façade — we detailed this step in our Saint-Michel article.
2. Where the outdoor unit goes, and what it sits on. A yard, a balcony, a rear façade, and a foundation wall do not have the same status or the same owner in a multi-unit building. This is the question that most often holds things up, and it must be settled before anything else.
3. Who owns the equipment. A system installed by a tenant in a home they do not own raises, at the end of the lease, a simple question that has no simple answer if no one has put it in writing: does it leave with the tenant, does it stay, and what condition is the wall left in? This should be written down beforehand, in one sentence, between the parties.
4. Who pays for maintenance, and who calls when it stops working. On a two-head system, rinsing the indoor filters is the occupant's task; the annual service visit is the owner's task. When no one has decided, no one does it.

What this changes technically

The answers to these questions genuinely change the way we work, and that is the point few contractors explain.

• Fewer penetrations, and better placed. In a home you do not own, every hole requires negotiation. We group the penetrations, reuse an existing opening when there is one, and position them so that future repairs are straightforward.
• Reversible choices whenever possible. A surface-mounted interior duct is less elegant than a concealed installation, but it can be removed without demolition and remains accessible for inspection with a screwdriver. We described its advantages and condensation pitfalls in our Saint-Louis-de-Gonzague article.
• A removable outdoor installation. A freestanding base, a removable bracket, a layout that is not cast into a slab: the unit must be able to be removed without leaving a structure behind.
• A complete photographic record of the initial condition, wall by wall, before the work. In a rental property, it is what settles end-of-lease discussions, and it takes five minutes.

The owner-occupant of a duplex

This is the most common case in Montréal-Nord, and it deserves a separate note.

A homeowner who lives in one apartment and rents out another in the same building must keep in mind that their unit and their tenant's unit are not independent of the building. The transmission of vibrations through a floor or a partition wall separating two apartments is the same mechanism we described for a party wall in our article on Sud-Ouest and for a foundation wall in the one on Vaudreuil-sur-le-Lac. An outdoor unit attached to the rear wall at the level of the apartment below can be heard by the tenant even though it serves the apartment above.

Our rule in a plex: we record the floor plan of both apartments before choosing the location, exactly as we record the neighbors' windows.

Two details in this photo that are worth a line

The unit is wedged into a corner, above a door frame. The geometry of a corner installation—better diagonal reach, but air intake taken from the most stagnant point in the room—is discussed in our article on L'Île-Bizard–Sainte-Geneviève, along with the adjustment of the vertical louvers that truly determines the direction of the airflow. Positioning above a door opening, with its questions about the lintel and clearance, is covered in our articles on Varennes and Verchères.

A curtain is hanging in front of the right-hand door. In an older dwelling, a curtain stretched across an opening is not decoration: it is an improvised thermal partition installed by the occupants to retain heat or cold in one room. Two things must be understood about it. It does not close off the room—it seals nothing at the top, sides, or bottom, so the room behind it must not be counted as a closed room. And it blocks the airflow, which is exactly the opposite of what is wanted if this opening is the path through which air must reach an adjacent room. This is a trade-off to discuss with the occupants during commissioning and record on the handover sheet.

Mistakes to avoid

1. Drill without looking at the ceiling first. A smoke detector fades into the background once you get used to seeing it.
2. Position an indoor unit so that it constantly blows on a detector, assuming the louvers can be redirected later.
3. Leave a detector exposed during drilling, then be surprised by nuisance alarms three weeks later.
4. Cover a detector's openings with tape to protect it, or forget to uncover it after the project.
5. Assume that the outdoor unit's A2L leak detector replaces a smoke detector.
6. Start work in a rental unit without written authorization from the building owner.
7. Do not write down what happens to the unit at the end of the lease.
8. Mount the outdoor unit level with the neighboring dwelling because it is the most convenient wall.
9. Treat a room enclosed by a curtain as an enclosed room.
10. Have it installed by an unlicensed RBQ contractor, which complicates both the manufacturer's warranty and any subsequent insurance claim.

HVAC maintenance

• Indoor filters: rinse every 4 to 8 weeks during the intensive-use season, depending on how the room is used. On a two-head system, this is an occupant task, demonstrated in person at the end of the project rather than described in a manual.
• Outdoor coil: clean annually. In a dense urban district, city dust accumulates without ever triggering an error code: capacity is lost without warning.
• Drain pans and drains: annual inspection of both indoor units, which operate in cooling mode only, plus the outdoor discharge point.
• Detectors: test using the button once a year, at the same time as the maintenance visit. This is the best time to do it because someone is already on site with a ladder.
• Run both indoor units in both modes for about thirty minutes each month, including during the off-season.
• Record for the file: serial numbers by unit, measured lengths, commissioning records, written authorizations, and photographs of the initial condition.

Grants and documentation

An efficient wall-mounted heat pump installed in a residence may qualify for residential assistance programs, particularly those offered by Hydro-Québec and Rénoclimat. The criteria and thresholds change regularly: we verify eligibility when the file is opened, without announcing an amount in advance. The Chauffez vert program is intended to replace fossil-fuel heating and does not apply to a dwelling already heated with electricity. In a rental building, eligibility also depends on the applicant's status, which is verified when the file is opened, not after the work is completed.

The SEER2, HSPF2, and EER2 ratings certify a combination of an outdoor unit and indoor units in a given configuration—which is why three series of AHRI codes are published by model—and the declared code must match what was actually installed. We developed this point further in our Saint-Anicet article.

Why entrust your installation to AirGreen

A smoke detector costs a fraction of what a heat pump costs, and it protects something priceless. A contractor who drills through a wall three feet from a detector without looking up has not stolen your money, but they have altered a safety device without telling anyone. This is the kind of thing we look at.

What we systematically put in writing before the work begins: the exact outdoor unit model, the capacity of each indoor head room by room, the planned routes and their lengths, the AHRI code corresponding to the actual configuration, the condition and position of the room's detectors, the authorizations obtained, the exact scope of the finishing work—and what the system will not do.

We work in Montréal-Nord, throughout the island of Montréal, in Laval, Longueuil, on the North Shore, and on the South Shore, providing HVAC installation, commissioning, and HVAC maintenance for wall-mounted and multi-zone systems.

Have your project assessed

If you live in a plex or apartment in Montréal-Nord and are considering a two-zone heat pump, two questions must be settled before requesting any quote: where the outdoor unit can be installed given the building and surrounding properties, and who must authorize the work. Contact AirGreen for an on-site technical assessment, a survey of the planned routes, and a detailed room-by-room quote.