Why More Ventilation Was Making This Sainte-Thérèse Home More Humid
In late July, we received a call from a townhouse owner in Sainte-Thérèse, a few minutes from the commuter rail station. The garden level felt clammy, a musty odor was settling into the storage area under the stairs, and droplets were beading on the cold-water pipe in the mechanical closet.
His reaction had seemed logical: he turned the air exchanger up to maximum speed and lowered the humidity setpoint. Three weeks later, the humidity had increased.
This result was not caused by faulty equipment. It was the physics of humid air, and it catches most homeowners off guard.
The screen reading when we arrived
The Lifebreath 99-DXPL02 digital control displayed, with the backlight on:
- Fan speed: 3 out of 5
- Measured relative humidity: 48%
- Dehumidistat setpoint: 45%
- Mode: 20 minutes of ventilation / 40 minutes of recirculation per hour
Humidity exceeded the setpoint by three points. The built-in dehumidistat was therefore doing exactly what it was designed to do: calling for more ventilation. And this additional ventilation was bringing in air from outside that was significantly more humid than the air inside the house.
The calculation we perform in front of every client in summer
Relative humidity is misleading because it depends on temperature. What matters when determining whether outdoor air dries out or dampens a house is the actual amount of water contained in that air, measured by the dew point.
| Air | Relative humidity | Approximate dew point | Water content |
|---|---|---|---|
| Outdoors, 24 °C | 75 % | ≈ 19 °C | ≈ 14 g/kg |
| Outdoors, 27 °C | 70 % | ≈ 21 °C | ≈ 16 g/kg |
| Indoors, 22 °C | 48 % | ≈ 11 °C | ≈ 8 g/kg |
A typical July day in the Laurentians therefore brings in air containing nearly twice as much water as the air inside the house. Every cubic foot introduced adds moisture, regardless of the fan speed.
A HRV (heat recovery ventilator) transfers heat between the two air streams. It does not remove water. It is not a dehumidifier, and no setting will turn it into a dehumidifier.
What we adjusted on site
- Dehumidistat setting raised for the warm season. A low setting in July forces the unit to ventilate continuously against more humid outdoor air. We raise the setting, or disable the function during the summer, then lower it again in the fall.
- Speed reduced from 3 to 1. The base airflow is more than sufficient for the code-required air exchange in a townhouse of this size.
- 20/40 mode retained. The 40 minutes of hourly recirculation circulate conditioned air from the ground floor to the garden level, evening out temperatures without introducing outdoor air.
- A portable dehumidifier installed on the garden level, set to 50%, with a hose draining to the floor drain. This is the appliance that actually removes the water.
- The occupants were instructed on the 20/40/60 override button for showers and cooking, rather than using high ventilation continuously.
Measured result ten days later: 44 to 46% in the garden level, condensation gone from the cold-water pipe, and the odor eliminated.
The ERV: the real answer to the summer humidity problem
This client then asked us the logical follow-up question: is there a unit that handles summer better?
Yes, to some extent. An ERV (energy recovery ventilator) transfers not only heat but also moisture between the two air streams. In summer, it reduces some of the incoming moisture and lowers the latent load placed on the air conditioner. In winter, it retains some of the indoor moisture.
The important distinction for southern Quebec: we are in climate zone 2, with cold winters and hot, humid summers. An HRV works perfectly here. An ERV is permitted, but absolutely requires a defrost system for prolonged subzero temperatures. An ERV without defrost installed in Sainte-Thérèse, Blainville, or Rosemère is a specification error, not a matter of preference.
Our position, after hundreds of installations on the North Shore: an ERV is an appropriate choice during a planned replacement, but never an emergency solution to a summer humidity problem. A properly sized dehumidifier costs a fraction of the price and works immediately.
Townhouse characteristics: the compact unit
In this type of building, the mechanical closet is narrow and the ceiling is often lowered. This is where the METRO 120D, the thinnest unit in the Lifebreath residential range, excels.
The METRO 120D specifications
- Cabinet thickness: only 9.75 inches, allowing installation in a suspended ceiling
- Airflow: 135 cfm at 0.2 in. w.g., 126 cfm at 0.4 in. w.g.
- Sensible recovery efficiency (SRE): 68% at 0 °C
- Apparent sensible efficiency (ASE): 81% at 48 cfm
- Power consumption: 62 W at low speed, 158 W at high speed, 1.4 A
- Weight: 37 lb, counterflow core, 5-inch collars
- Recirculation defrost
Three METRO-specific installation constraints that we often see improperly handled
The supports. METRO models cannot be suspended using the 99-80-102 straps supplied with MAX and RNC units. They require mounting brackets. We regularly find Metros suspended from straps, with the resulting vibration and structural noise.
The drain. The METRO 120D has a single drain connection with a 1/2 in. outside diameter, whereas most units have two. This single drain must be properly trapped and sloped toward the floor drain. A missing trap allows odors to rise; a reverse slope causes the pan to overflow during defrosting.
Balancing. The METRO 120D, METRO 120F, and RNC 95 are the three models without balancing ports in the door. Balancing therefore cannot be done using the usual method. It requires an airflow measurement station—models 99-150 (5 in.) through 99-155 (8 in.)—or a Pitot tube with the 99-168 kit. Without this equipment, a technician cannot claim to have balanced a Metro. They adjusted it by guesswork.
A single wall opening with the 99-190 double cap
Townhouses have little exterior wall area, and the façade is often governed by condominium aesthetic rules.
The 99-190 dual cap meets this requirement: it combines the fresh-air intake and stale-air exhaust in a single 6-inch opening, with damage-resistant metal construction and rigid plastic duct connections. The 99-194 is the version for 4-inch connections.
Two considerations to know before specifying it:
- It is limited to 100 cfm. Above that, two separate weather caps are required—99-185 (5 inches), 99-184 (4 inches), or 99-186 (6 inches).
- Lifebreath recommends confirming acceptance with the competent municipal authority. Some municipalities require physical separation between the intake and exhaust. We systematically verify this before ordering.
The distribution: Techgrilles 99-EAG5 on 5-inch ducts
The METRO's 5-inch collars require 5-inch ducts, and therefore Techgrilles Lifebreath 99-EAG5 grilles. The range includes the 99-EAG4 (4 inches), 99-EAG6 (6 inches), and 99-EAG8 (8 inches).
In this townhouse, we took advantage of the service call to:
- Replace a fixed grille on the walkout level with a 99-EAG5, whose adjustable center cone allows the airflow to be adjusted room by room
- Install a Terminator 99-TM5 fitting in the corridor ceiling, where the structure did not allow the grille to be inserted directly into the duct
- Shorten two excess sections of flexible duct that were absorbing a significant portion of the available pressure
The compression spring clips on Techgrilles eliminate exposed hardware and allow hand removal for maintenance—especially valuable in a condominium suspended ceiling.
The mistakes we correct most often during hot weather
- Lowering the humidity setpoint in July. The unit ventilates more and brings in more humid air. This is the opposite of the intended effect.
- Using the air exchanger as a dehumidifier. The HRV transfers heat, not water. Dehumidification is handled by air conditioning or a dedicated appliance.
- Strongly ventilating a damp basement or walkout level in summer. Warm outdoor air meets cool surfaces and condenses on foundation walls.
- Neglecting the condensate drain trap. Backdrafting odors, overflow during defrosting, and water damage to a finished ceiling.
- Never clean the filters. The supply and exhaust filters are washable. MERV 8 pleated replacement filters are available: 99-MERV8-6 for square cores and 99-65-186 for HEX cores.
- Ignore the service indicator on the 99-DXPL02. The maintenance reminder and dedicated RESET button exist precisely to prevent the issue mentioned above.
Reliability, compliance and financial assistance
Lifebreath units are HVI-certified, comply with CSA and UL standards, are manufactured under ISO 9001, and are covered by a lifetime warranty on the recovery core as well as a 5-year warranty on replacement parts. The cabinet is made of pre-painted 20-gauge galvanized steel and insulated to prevent exterior condensation.
Regarding rebates, installing or replacing an HRV may qualify for the Rénoclimat program, provided that the initial energy assessment is completed before the work begins. In a condominium, the process sometimes involves the condominium association, and we verify eligibility for the file before scheduling a date.
What this Sainte-Thérèse project highlights
At the end of the visit, the homeowner asked us why no one had explained this when they bought the house. It is the most common question in our trade, and it is rarely about the equipment itself.
A heat recovery ventilator is operated differently depending on the season. In January, it removes excess humidity produced by the occupants. In July, it cannot do anything about outdoor humidity and should be left at its basic airflow rate while the air conditioner and, if necessary, a dehumidifier do the work. The same unit, two opposite operating principles, a single wall control.
At AirGreen, we carry out HVAC installation and HVAC maintenance work in Sainte-Thérèse, Blainville, Rosemère, Boisbriand, Lorraine and Bois-des-Filion, throughout the North Shore, as well as in Montreal, Laval, Longueuil and across the entire South Shore. We take measurements, make seasonal adjustments, and leave the customer able to operate their system without having to call us again.