Is Poor Ventilation Dangerous? Indoor Air Quality Explained

Published By: Debbie Luna
Last Updated:
March 18, 2021

Ensuring that a space is properly ventilated helps to improve indoor air quality. Poor indoor air quality can have serious health implications due to the build-up and prolonged exposure to volatile organic compounds like mold.

Poor ventilation in the home is dangerous. Lower air exchange rates increase the concentration of airborne pollutants. Environmental factors like climate, humidity, and temperature all affect when home-owners decide to either naturally or mechanically ventilate their space. Poor ventilation can also result in moisture build-up and mold growth.

It’s important to have an understanding of how the air in your home/place of business functions.

How Air Moves Through Your House

All homes exchange indoor air with the outdoors. Air exchange occurs in two ways: air leaks and temperature and pressure differences.

All homes have air leaks or passages by which air can travel through. Examples include around pipes and plumbing, chimneys, vents, as well as cracks that form between structures like windows and walls.

frost window moisture

Temperature and pressure differences help to move air in and out of buildings through a phenomenon known as the Stack Effect. In laymen terms, the stack effect is essentially how warm air moves upward in a building due to air buoyancy.

This occurs because warm air is lighter than cold air. As warm air escapes the upper levels through air leaks it reduces the pressure in the ground floor which causes air to infiltrate.

Essentially, cold air infiltrates the ground floors and causes warm air to ex-filtrate on the upper floors.

Signs of Poor Ventilation

These signs are usually indicative of a home that has poor ventilation:

  • Windows and glass that appear frosted due to condensation
  • The discoloration of floor, wall tiles, and grout
  • Early signs of rust stains on plumbing
  • Mold growth on structural surfaces like walls and wood
  • Strong odors that don’t dissipate
  • Heat build-up that doesn’t dissipate

Types of Ventilation

There are three types of ventilation used to help combat airborne pollutants and humidity: spot, dilution, and natural.

Spot Ventilation

Spot ventilation targets a specific source of air pollution/moisture. Examples include a range hood above a stovetop, an exhaust fan in a bathroom, or the exhaust (duct-work) for a clothes dryer.

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) recommend intermittent or continuous ventilation rates as follows:

  • Bathroom: 20 (Continuously) – 50 CFM (Intermittently)
  • Kitchen: 100 CFM (Intermittently) or 5 Air Changes per Hour (ACH Contiously)

Dilution Ventilation

Dilution ventilation is capable of supplying and exhausting large amounts of air from a building. The overarching goal is to dilute the concentration of airborne contaminants through air changes.

An air change occurs through natural ventilation as well as mechanical ventilation.

Natural Ventilation

Natural ventilation is the uncontrolled movement of air in a space. Air naturally infiltrates a building or structure through air leakage. However, homes today are engineered to be more energy efficient so that air leaks and the subsequent thermal energy loss are nullified.

This also means that air can’t naturally infiltrate a space. By opening windows and doors you allow for natural ventilation to occur. Meaning, fresh air enters the space and polluted air exits.

Natural ventilation does have limitations and essentially relies on ambient temperature, wind, and how air-sealed your home is. Many people opt to go the route of mechanical ventilation instead.

natural ventilation open windows

Mechanical Ventilation

Mechanical or whole-house ventilation is capable of providing uniform ventilation throughout the space. These systems are comprised of exhaust fans and duct systems to perform air changes.

There are four mechanical ventilation systems used: exhaust, supply (intake), balanced, and energy recovery.

An exhaust ventilation system works to depressurize the building. Inversely, a supply ventilation system works to pressurize the building. A balanced system does neither, rather they introduce and exhaust fresh and polluted air.

An energy recovery ventilation system is capable of ventilating a space while minimizing energy loss.

Reasons Poor Ventilation is Dangerous

Poor ventilation can have a negative impact on your home and work space as well as your health.


Condensation occurs when warm air collides with a cold surface. It also occurs due to high levels of humidity and lack of ventilation.

Condensation is most noticeable on structural surfaces like windows. However, it can manifest itself on walls, carpets, flooring, wallpaper, and furnishings.

Condensation can also become trapped in porous materials and build-up over time. This can cause timber to rot and swell and cause metal to oxidize and rust.  It can also lead to the growth of mold.

The easiest way to combat this is by ventilating the space. Open windows and doors and use a dehumidifier to remove moisture from the air.

For spaces like attics, this can be especially problematic. It's a dark, warm space that can be prone to moisture-build and mold growth. These spaces will commonly have intake and hot air exhaust vents to combat this problem.

Mold Growth

brick wall mold

Mold thrives in humid climates due to condensation and moisture. In order for mold to grow it requires water, a food source, and oxygen. Only one of these factors can be eliminated: moisture.

Building materials like drywall, wood, and paper are carbon-containing which mold can consume as a nutrient source. Mold are obligate aerobes and require oxygen in order to survive. With that said, even if you reduced oxygen in the atmosphere, mold can also thrive in low levels of oxygen.

Adequate ventilation prevents environmental factors like humidity levels and condensation that results in moisture build-up.

Mold exposure has cold-like symptoms. These symptoms become exacerbated in individuals who are allergic to mold.

Low Oxygen Levels

Poor ventilation can result in the build-up of carbon dioxide and result in little oxygen. Symptoms of low oxygen levels include shortness of breath, headaches, and fatigue.

Airborne Contaminants

There are both indoor and outdoor contaminants that can become trapped in your home or work space due to poor ventilation.

Examples of indoor contaminants include:

  • Emissions from glues, cleaning supplies, and particle board used during construction.
  • Appliances that use gas as a fuel source like cooking range, furnace (wood-based too), or water heater.

Examples of outdoor contaminants include:

  • Allergens and particulates
  • Mold spores
  • Dust particles (primarily comprised of dirt and pollen)
Debbie (Deb) started powerlifting and Olympic lifting in High School as part of her track team's programming; She continues to train in order to remain athletic. Inspire US allows Deb to share information related to training, lifting, biomechanics, and more.
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