An invisible threat under your feet: how humidity turns your basement into a ticking time bomb
In Montréal, Laval, Longueuil, and across the North Shore and South Shore, we see homeowners every week complaining about unpleasant smells, damp walls, or suspicious black spots in their basement. The cause? Poor ventilation—often overlooked, yet silently turning your basement into the perfect breeding ground for mold. At AirGreen, we’ve installed air exchangers in hundreds of homes where indoor air quality had dangerously deteriorated. And each time, the results were immediate.
The problem: stale air gets trapped
A poorly ventilated basement traps humidity, pollutants, spores, and gases (like radon). This combination creates an ideal climate for microscopic fungi to grow in:
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Structural wood
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Wall insulation
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Laminate flooring
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Hidden cavities behind drywall
It’s no coincidence that symptoms like allergies, asthma, and chronic fatigue increase in homes with poor ventilation.
Case study: AirGreen intervention in Rosemère
In a detached home in Rosemère, the owners had been struggling with a persistent damp, earthy smell, despite multiple deep cleanings. During our inspection, we recorded a 78% humidity level in their finished basement. The gypsum walls showed mold traces invisible to the naked eye but detected with a thermal camera. Our team installed a Venmar VHR PRO 200 air exchanger with dedicated basement ducting. In under 72 hours, the odors were gone, and humidity levels dropped below 50%.
Why are basements the most affected?
It’s simple: cold air naturally sinks. That makes the basement a place where humidity accumulates and stagnates. Add to that:
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Small or no windows
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Imperfect foundation sealing
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Porous materials (concrete, wood) that retain moisture
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No mechanical ventilation originally installed
This combination turns most Québec basements into fungal spore traps.
Real health risks
What we breathe in a contaminated basement rises to the entire home. Without a high-performance air exchanger, you create what’s called a reverse chimney effect, where polluted air spreads into the upper floors.
Possible consequences include:
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Respiratory issues
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Allergic reactions
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Frequent headaches
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Damage to your home’s structure
Testimonials and AirGreen installations across Greater Montréal
Montréal (Ahuntsic-Cartierville)
Installation of a Lifebreath 195 ECM HRV in a duplex with a finished basement. The client had repainted several times without getting rid of recurring mold spots. After installation, we saw an instant improvement in air quality, with humidity dropping to 42%.
Laval (Sainte-Dorothée)
Bungalow with basement turned into a playroom. Persistent odor issues. We installed a Venmar EVO5 air exchanger, with direct intake and exhaust for the basement. The children stopped complaining about sore throats by the end of the first week.
Longueuil (Vieux-Longueuil area)
Semi-detached house with a partially excavated basement. Our technicians discovered mold behind wood panels, caused by insufficient passive ventilation. Installing a high-efficiency wall-mounted air exchanger resolved the problem for good.
What you can do right now
1. Assess smell and humidity
A healthy basement should never smell. If there’s a constant musty odor, you're likely at risk.
2. Check the materials
Warping wood, bubbling paint, lifting floors: these are signs of chronic condensation.
3. Measure the humidity level
AirGreen offers free inspection visits, including humidity measurement, current ventilation assessment, and customized recommendations.
4. Install a proper air exchanger
We offer compact, energy-efficient models, designed for basements, with built-in humidity control.
Why an air exchanger is the best solution
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Continuously refreshes basement air without heat loss
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Eliminates excess humidity, odors, spores, and VOCs
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Prevents long-term mold growth
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Improves air quality throughout your entire home
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May be eligible for Québec government grants
The AirGreen approach: efficient, fast, and long-lasting
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We inspect your basement for free
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We install the best unit for your space (brand, power, capacity)
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We provide a turnkey service, from analysis to final setup
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We serve all of Greater Montréal, including the North Shore and South Shore
AirGreen: the reference for basement air exchangers in Montréal, Laval, Longueuil, North Shore, and South Shore.