Installation of a GREE FreeMatch R32 2-head wall-mounted heat pump in Saint-Ours (Pierre-De Saurel RCM, Montérégie)

Frost is not a matter of cold; it is a matter of humidity—and Saint-Ours is a village surrounded by water

Almost every customer who calls us in November to report that their heat pump is “defrosting all the time” has the same assumption in mind: it is cold, so the unit freezes. The opposite is true. An outdoor coil does not become covered in frost because the air is cold, but because the air is humid and the heat exchanger surface has simultaneously fallen below the dew point and below freezing. Cold air contains very little water vapor. At −25 °C, there is almost nothing to deposit on the coil. At +2 °C in light rain, there is a great deal.

That is why the most demanding operating window for a wall-mounted heat pump in Quebec is not during the coldest nights of January, but in the approximate range of −5 °C to +5 °C in saturated weather: autumn fog, freezing drizzle, February thaws, and November mornings by the water. In Saint-Ours, this range is not a meteorological abstraction: it is the local climate of a village built on the east bank of the Richelieu River, approximately 23 kilometers upstream from Sorel, opposite Darvard Island and the dam that regulates the river for 45 kilometers to Chambly.

This installation, carried out in a village home in Saint-Ours, was therefore designed first and foremost around that reality.

What we installed

The electric baseboard heaters were retained in the bedrooms, bathroom, and basement. We never remove them during the first season: they are the building's peak-capacity reserve and freeze protection when the occupants are away.

Why the GWHD(30) and why two 18,000 heads

The open volume on the ground floor of an old village house is not one room; it is three rooms whose partitions were removed at some point. It connects via an open staircase to the upper floor, which also behaves as a single volume. Two actual zones, two heads, and no benefit to multiplying the heads in a building with only two volumes to condition.

The choice of 18,000 + 18,000 on a 30,000 compressor is based on the assumption of non-simultaneous operation: the two floors never call for their full capacity at the same time. The compressor modulates from 8,190 to 40,900 BTU/h in heating mode, providing both the capacity to handle a −22 °C morning and the ability to ramp down very low during the shoulder season without short cycling. This low range matters most in a village house: most heating hours in a year occur between −5 °C and +8 °C, not at the extremes.

The 35 A MOCP also played a role. In an older building with a 100 A service entrance, the difference between 35 A and 45 A often determines whether the project requires an electrical service upgrade. The Code load calculation is the responsibility of the master electrician; our contribution is the manufacturer's data sheet, and we never estimate it in their place.

What the frost really costs, and when

A defrost cycle briefly reverses the operation: the outdoor coil becomes hot, the ice melts, the water falls into the base pan and exits through the bottom of the unit. During this time, the unit does not heat the house. Three practical consequences that we systematically explain before the work:

• The frequency is not constant. A unit may run several defrost cycles per hour during a foggy day at +1 °C, and almost none during a dry week at −18 °C. A customer who judges their unit based on the November week is judging it at its worst moment.
• The water produced always accumulates in the same place. Each cycle releases roughly a few hundred milliliters to a few liters, depending on the thickness of the frost. We do not publish a design value for this because it depends on the site; what we retain is that on a humid day, several liters collect at a single point, freeze, and start again the next day.
• The steam plume is normal. A unit that “smokes” during defrost always worries people the first time. We show the customer a complete cycle before leaving the site rather than simply describing it.

What we do differently on a wet site

This is where the Saint-Ours site changes the implementation, not just the message:

1. The height of the base is chosen based on ice behavior, not a standard value. On wet ground, it is not snow that determines the height, but the ice sheet that defrosting rebuilds every night. We deliberately leave more clearance beneath the chassis than we would on a dry site. (This should not be confused with the issue of the flood elevation, which is an entirely different subject governed by different rules—we covered it on our riverside pages for Ormstown and Sainte-Marthe-sur-le-Lac.)
2. A bed of clean stone beneath the unit, so defrost water infiltrates instead of spreading out and forming another ice sheet.
3. The airflow never points toward a pedestrian walkway. A humid plume in February settles and freezes on whatever it touches.
4. Annual coil rinsing becomes an installation requirement, not a suggestion. A coil that goes through fifty to one hundred freeze-thaw cycles per season retains debris that water redistributes among the fins.
5. No enclosure, screen, or decorative shelter. An enclosed unit cycles through defrosts more frequently without ever producing an error code that says, “I’m inside a box.”

The mistakes we see most often on this type of site

• Place the outdoor unit directly on a concrete slab at ground level, putting it in its own ice tray as soon as the first thaw arrives.
• Directing the water outlet toward a foundation or a garage door.
• Concluding that a unit defrosts “too much” and calling in a technician in November, even though the behavior is normal and the same unit will be quiet in January.
• Adding refrigerant “as a precaution” when the developed length is below the factory charge threshold. Here, 33 m out of 40 m: nothing was added, and the minimum room-size check required by the A2L classification of R32 was redone using the factory charge of 2,200 g.

What blown air does to the furniture in front of it

We have already written, for an installation near Saint-David, about what happens when a piece of furniture eventually ends up in front of a wall-mounted head and blocks its airflow. This page deals with the opposite situation, and to our knowledge no one writes about it: what the head does to the furniture.

In this house, the main-floor head is mounted high in a corner, and the object immediately beneath its airflow is a solid-pine hutch with a glass door and a projecting cornice, used as a dry pantry. This is not a decorative detail: it is the surface that receives the most moving air in the entire room, several thousand hours per year.

Solid wood moves, and a constant stream of air makes it move from only one side

A wall-mounted unit does not dry out the air in the house while heating: the indoor coil is warm, nothing condenses on it, and the building's water-vapor content does not change by a single gram. So this is not about relative humidity, but about air velocity. Evaporation from a material's surface depends directly on the movement of the air flowing across it.

Effect on a solid-wood panel: the side exposed to the airflow loses its moisture faster than the back side. A moisture gradient develops through the thickness of the panel, and a panel that dries on only one side warps. In an antique piece of furniture, whose joints were glued at a relative humidity level the house has not had for a long time, this results in joints opening, a door that no longer closes in February and closes again in July, and sometimes a crack in a back panel. Nothing spectacular, nothing sudden, and nothing the customer associates with their heat pump.

Other objects that do not like a permanent airflow

• A piano or a soundboard instrument. The soundboard is a thin wooden panel under tension. No instrument should be placed in the discharge path of a wall-mounted head, in either cooling or heating mode.
• Paper: books, sheet music, photographs, documents. Continuous airflow carries and deposits dust, and an exposed binding dries out like a piece of furniture.
• Dry goods stored uncovered. We published the strict rule for commercial food areas on our Pointe-des-Cascades page: never blow air directly onto uncovered food. In residential settings, the reasonable version is simply to use a closed container.
• Glass and metal, in cooling mode. An airflow at approximately 12 °C directed at a glass door can locally bring the surface below the room’s dew point, causing the glass to fog in midsummer even when nothing is defective.
• Plants, which we have addressed elsewhere (Saint-Polycarpe): yellow leaf tips in a permanent airflow indicate air movement, not a defective unit. Move the plant; do not lower the setting.

The rule: sweep across a room; do not aim at an object

A properly adjusted unit circulates the air in the space; it does not point at anything. Specifically, on this project:

1. The head’s position was determined with the existing furniture in mind, not only the manufacturer’s clearances and the windows.
2. The louvers were adjusted forward rather than downward in cooling mode, and the oscillation was left active rather than fixed in one direction.
3. The room information sheet given to the customer now names the objects, rather than only the room, the head, the installation height, and the free volume in centimetres. This is an addition we are making as of this project.
4. The question is asked again at every annual maintenance visit: “What has been moved in front of the unit since last year?”

Three things we refuse

• Recessing a wall-mounted head into a niche or decorative cabinet, regardless of the aesthetic argument.
• Correcting a furniture-related problem by changing the setting. Lowering a setting to compensate for a perceived issue solves nothing and increases the bill.
• Mounting a head above a piece of furniture that would have to be moved to open the front panel or rinse the filter.

A village of 1,723 people, and a built environment that determines everything

Saint-Ours has 1,723 residents according to the 2021 census, up 3.2% over five years, spread across 59.23 km² and 858 private dwellings. The seigneury was granted to Pierre de Saint-Ours, an officer in the Carignan-Salières Regiment, between 1667 and 1672; the parish was canonically established in 1831, and the village became a town in 1866. The 1792 manor, enlarged in 1845 and 1870, was designated a cultural property in 1982 as the only intact ensemble of the foundations of a Québec seigneury, and the 1878–1882 neo-Romanesque church has a 185-foot steeple.

This is not just local colour. A housing stock of 858 units in a village founded in the 17th century means that most buildings have walls, partitions, ceilings and electrical services that bear no resemblance to those of a 2005 development. Every heat pump installation in Saint-Ours is decided down to the centimetre, on site, and a quote made over the phone based solely on the building's area is worthless.

Grants and eligibility

The installed unit is ENERGY STAR and AHRI certified, which is the entry requirement for most programs currently in effect in Québec, including Hydro-Québec's LogisVert and Rénoclimat. Actual eligibility nevertheless depends on the type of heating being replaced, the building's file and the terms in effect when the work is carried out: we verify it case by case before promising it, never based on a brochure.

AirGreen in Saint-Ours and the Pierre-De Saurel RCM

We serve Montréal, Laval, Longueuil, the North Shore and the South Shore, and the Pierre-De Saurel RCM — Sorel-Tracy, Saint-Ours, Saint-David, Yamaska, Massueville, Saint-Robert, Sainte-Victoire-de-Sorel, Saint-Aimé, Saint-Gérard-Majella — is part of our territory for HVAC sales, installation and maintenance. Our teams hold the required RBQ licences, and every wall-mounted heat pump installation concludes with documented commissioning, a file provided to the customer, and warranty registration.

For an assessment in Saint-Ours or elsewhere in Montérégie, write to us at sales@airgreen.ca.