We brought the ventilation of a Repentigny home back to life by changing just one component: the wall control
On the hallway wall of this Repentigny home, the outline of the old control is still visible: a rectangle of whitewashed plaster and two abandoned screw holes. The old housing was wider, taller, and above all much more opaque. A humidity dial graduated from 20 to 80, a three-position switch, and no indication of what was actually happening.
The homeowners told us plainly: they never touched it. The dial had remained in the same position since they bought the house, eight years earlier.
Their air exchanger, a LIFEBREATH RNC 155, was nevertheless in perfect working order. Clean core, quiet motors, healthy ductwork. The system's only faulty component was the interface. We therefore replaced the wall control with a model featuring indicator lights, reprogrammed the modes, adjusted the humidity setpoint, and rebalanced the system.
The result, three weeks later: no more condensation on the basement windows, and the temperature difference between the basement and the main floor cut in half. Without touching the unit.
What the old control prevented
An older-generation wall control does only one thing: it starts the unit at one speed, with a fixed humidity threshold. It provides no information and offers no modes.
The installed control offers, on a single plate:
- A continuous low-speed mode (LO) — the unit ventilates continuously at a low airflow rate.
- Partial-cycle modes, identified by percentage, in which the unit ventilates for a fraction of each hour rather than continuously.
- A 20/40 mode, alternating 20 minutes of ventilation and 40 minutes of recirculation.
- A recirculation mode identified by its own indicator light.
- Humidity-based control, accessible via the droplet-shaped button.
- A settings menu beneath the gear button.
- Green indicator lights that continuously show the active mode and current speed.
This last point is what changes everything in real-world use. A control that displays its status is a control the occupants understand—and therefore use. In the photo taken after commissioning, three indicator lights are on: continuous low speed, medium speed, and the 20/40 cycle active. One glance is all it takes.
Recirculation mode, finally explained
It is the least understood function of all the air exchangers sold in Quebec, and yet one of the most useful in January.
What it is
In recirculation mode, the appliance does not introduce outdoor air. It circulates the air already in the house: it draws air from certain areas and redistributes it to others through its own network of ducts.
In other words, it works like an air circulator for the entire house, with no energy penalty from reheating cold air.
When we use it
In very cold weather. When outdoor air drops below –20 °C, it contains almost no water vapor. Ventilating continuously dries out the house very quickly. Alternating ventilation and recirculation maintains sufficient air exchange while slowing the drying process. That is exactly the logic behind 20/40 mode: 20 minutes of fresh air, 40 minutes of indoor air circulation.
To even out temperatures between floors. In this house in Repentigny, the difference between the finished basement and the bedroom floor reached several degrees in winter. By moving the warm air accumulated upstairs downward, recirculation reduces this difference without consuming more heating energy.
During periods of poor outdoor air quality. A smoke event, agricultural spraying in nearby areas, or roadwork close by: recirculation allows you to continue circulating and filtering indoor air without introducing outdoor air for a few hours.
What recirculation does not do
This needs to be made clear, because the confusion is common and can lead to improper use:
- It does not bring in any fresh air. CO₂ and volatile organic compounds continue to accumulate while it operates.
- It does not replace ventilation. An appliance left in continuous recirculation throughout the cold season is equivalent to not ventilating at all.
- It does not dry out the house. If indoor humidity is too high, only ventilation with outdoor air will lower it in winter.
That is why we never program recirculation alone as the default mode. It is used alternately or occasionally.
Humidity-based control: the setting that must change with the season
The droplet-shaped button provides access to the humidity setting. When indoor relative humidity exceeds the target, the unit automatically increases its airflow until it drops below the threshold.
The most common mistake in Quebec: setting the target once and never touching it again. A 40% setting works in October and becomes a source of condensation in January because the temperature of interior surfaces—glazing, frames, and corners of exterior walls—drops as the outdoor temperature falls.
Here is the chart we leave with our customers and review with them during commissioning:
| Outdoor temperature | Indoor relative humidity setting |
|---|---|
| 0°C and above | up to 40 % |
| –1°C to –10°C | approximately 35 % |
| –11°C to –20°C | approximately 30 % |
| –21°C to –30°C | approximately 25 % |
| below –30°C | approximately 20 % |
The rule of thumb that sums it all up: if condensation appears along the bottom of the windows in the morning, the setting is too high for the current weather. Lower it by 5% and monitor for two or three days.
We also recommend that homeowners adjust the setting two or three times per winter rather than continuously—at the first deep freeze, in the heart of January, and during the spring thaw. Three adjustments per year, each taking less than a minute.
What gets set once on an RNC 155—and never revisited
LIFEBREATH RNC 155 Specifications
| Specification | Value |
|---|---|
| Type | HRV (heat recovery ventilator), ENERGY STAR certified |
| Net supply airflow | 163 CFM at 0.2 in. w.g. · 146 CFM at 0.3 · 132 CFM at 0.4 |
| Apparent sensible effectiveness (ASE) at 0°C | 84 % (at 59 CFM) |
| Sensible recovery efficiency (SRE) at 0°C | 75 % (at 59 CFM) |
| Core | Patented counterflow HEX, removable for cleaning |
| Power supply | 115 V / 60 Hz, 1.4 A |
| Power consumption | 66 W (low speed) / 118 W (high speed) |
| Defrost | Recirculation (damper) |
| Configuration | Horizontal, balancing ports on the door |
| Dimensions | 19 in. H × 33.6 in. W × 14.75 in. D |
| Weight | 71 lb (32.5 kg) |
| High speeds | 3 settings selectable by the installer |
| Filters | Washable, on both air streams |
| Suspension | Adjustable straps and S-hooks, four threaded inserts |
| Drain fittings | 2 × 1/2 in. (12 mm) |
| Control wiring | 3 wires, minimum 20 gauge, maximum 100 ft |
Two figures deserve comment.
84% apparent sensible efficiency at 0 °C. This is a high value, supported by the counterflow HEX core, whose geometry circulates the two airflows in opposite directions along their entire length rather than at right angles. Thermal contact is extended, so heat transfer is more complete.
66 W at low speed. On a unit that must run continuously, this is the figure that matters on an annual utility bill—far more than the power at high speed, which is only called upon intermittently.
The three selectable high speeds: the invisible setting
The RNC 155 allows the installer to choose, during commissioning, which of three high speeds the unit will use when it switches to maximum operation. The factory setting is the highest speed.
It is a parameter the owner never sees, that no wall control displays, and that explains why two identical homes equipped with the same unit can behave very differently.
Why we sometimes reduce it:
- Noise. In a short duct system, maximum speed can generate whistling at the grilles. Lowering it by one setting eliminates the noise without compromising the required airflow.
- Wintertime drying. A unit that ramps up too high every time the humidity threshold is triggered causes relative humidity to fall below the target.
- Matching the airflow calculation. If the house requires 130 CFM and the maximum speed delivers 160, we maintain an unnecessary permanent over-supply.
Why we sometimes leave it at maximum: in a long duct system with many elbows, or in a densely occupied home, the reserve is necessary.
At this Repentigny project, we lowered it by one setting. The ductwork was short, the factory maximum speed produced a whistling sound at the main bedroom grille, and the required airflow was still achieved.
Balancing at the door ports
The RNC 155 is equipped with balancing ports directly on the unit door, allowing measurements without dismantling anything or drilling into the ducts.
Our method: measuring at both ports at high speed, reading the pressure-flow relationship, adjusting, taking a second measurement, then recording the values on a sheet left with the owner along with the date and technician identification.
In this house, the unit had never been rebalanced since construction. The measured difference between supply and exhaust exceeded 15%, leaving the house permanently depressurized and explaining some of the condensation observed in the basement.
Recirculation defrost and the two drains
The RNC 155 uses damper-based recirculation defrost. During the anti-frost cycle, a motorized damper closes off the outdoor air intake and circulates indoor air through the core to defrost it. The house is not depressurized during the operation, unlike units that simply shut off the supply fan.
This mechanism has one practical implication: the unit produces condensate and requires connected drains. The RNC 155 has two 1/2 in. connections. We connect them with separate, primed traps, on a continuous slope, with regular supports.
On units returned to service, this is the first thing we check. A clogged drain or a trap that has lost its prime on a unit with recirculation defrost eventually allows water to accumulate in the cabinet.
Mistakes to avoid
- Replacing the unit when only the control is outdated. An eight- or ten-year-old air exchanger in good condition deserves an evaluation of its interface and settings first.
- Leaving the humidity setpoint fixed all year. This is the primary cause of wintertime condensation on windows.
- Using recirculation as the primary mode. It does not bring in fresh air.
- Ignoring the installer's high-speed setting. It determines noise, drying, and actual airflow.
- Never rebalance. A 15% difference between the two airstreams is invisible and permanent.
- Neglecting both drains and their traps on a unit with recirculation defrost.
- Install the new control without redoing the wiring. Lifebreath controls operate on three wires, minimum 20-gauge, over a maximum run of 100 ft. Original wiring that is undersized or too long causes erratic behavior that no one associates with the cable.
Maintenance
- Every three months — wash the filters for both airstreams. They are washable, eliminating a recurring cost, but only if they are actually washed.
- Every six months — remove and clean the core counterflow, check both drains and their traps, and inspect the defrost damper.
- Annually — inspection of exterior hoods, verification of the insulation and vapour barrier of the exterior ducts, revalidation of airflow rates at the door ports, and review of the humidity setting with the homeowner.
Compliance and programs
For new homes covered by the Quebec Construction Code, balanced mechanical ventilation is required, and it is a condition of the Novoclimat program. For an existing home like this one, modernizing a control or rebalancing a unit does not fall under a subsidy program — these are maintenance and optimization interventions. They remain among the most cost-effective services we perform, precisely because they cost a fraction of a complete replacement.
We systematically confirm the order of the work with the client when a broader project is being considered, especially when a heat pump or insulation work is planned, because the sequence affects eligibility for current programs.
For your project in Repentigny or elsewhere on the North Shore
At AirGreen, we always start by assessing what can be salvaged. A unit in good condition that is poorly controlled, improperly adjusted, or incorrectly balanced accounts for a significant share of the systems we inspect in Repentigny, Le Gardeur, Charlemagne, L'Assomption, and throughout the North Shore. The solution is often a modern control, documented rebalancing, and twenty minutes of explanations for the occupants.
When replacement is necessary, we say so too, with the numbers to back it up.
We carry out HVAC installations — air exchangers, wall-mounted and central heat pumps, air conditioners, and heating systems — in Repentigny, Montreal, Laval, Longueuil, throughout the North Shore and the South Shore. Licence RBQ # 5645-9605-01.
To have your LIFEBREATH air exchanger settings evaluated or to get a quote, call us at (514) 316-2973 or email sales@airgreen.ca.