For healthier indoor air quality, choose the right ventilation strategy

For home builders and contractors seeking to deliver healthy homes, installing powerful ventilation that assures good indoor air quality (IAQ) and energy efficiency is a must. In fact, at a recent IAQ conference for the building trade, many of the nation’s leading green builders ranked the indoor air we breathe as important to our health as the food we eat.

Stale polluted indoor air from moisture and harmful substances can cause a home to become unhealthy and even toxic. A properly-ventilated home offers energy savings and many health benefits of improved indoor air quality such as relief from dizziness, headaches, nausea, asthma and other serious respiratory issues.

“New homes today are very energy efficient, which requires them to be built nearly airtight,” says Panasonic BPI Certified Building Analyst, Ken Nelson. “That’s great news for your utility bill, but not so great for the quality of air you’re breathing inside your home. The lack of natural ventilation can trap all kinds of toxins inside.”

Enter into the building equation mechanical ventilation, which draws out pollutants and draws in fresh air in a controlled manner. Now that homes are built tighter due to energy-efficient building codes, you cannot rely on airflow through small holes or cracks in walls, roof or windows.

“Without mechanical ventilation to provide fresh air, moisture, odors, and other pollutants can build up inside a home,” says Nelson. “Mechanical ventilation systems circulate fresh air using ducts and fans, rather than relying on airflow leakage through a home's natural cracks and crevices.”

An effective IAQ solution requires more than installing a single exhaust fan in the bathroom. There are three primary strategies for controlled ventilation: exhaust, supply, and balanced systems. Let’s look at the nuts and bolts of each…

Exhaust ventilation removes pollutants at the source. An inexpensive and simple approach to ventilating a house, it works by drawing up and forcing air out of the home. A common example would be an exhaust fan in a bathroom or kitchen. Exhaust fans depressurize the home’s interior, which then gains make-up air through passive vents such as air leaks in the building envelope.

Because this strategy only actively exhausts air, it is not recommended in hot or humid climates. Since any make-up air is gained passively, that air may be humid, contain pollutants or be too cold, leading to energy penalties for the home and discomfort for its occupants.

Supply ventilation dilutes pollutants. Another simple and inexpensive approach, this strategy uses a supply fan to pressurize a home, actively bringing fresh outdoor air inside. Supply ventilation offer better control over pollutants present in incoming air, as they only obtain outdoor air through specified vents. Pressurizing the house more readily forces out combustion gases and other contaminants.

The downside? Supply ventilation struggles with conditioning or removing moisture from incoming air, and can raise heating and cooling costs due to leakage. This is particularly prevalent in older homes where building envelopes are more porous compared to today’s tighter sealed energy efficient structures.

Indoor environmental professionals and air quality experts generally agree that a balanced ventilation strategy is best. Balanced ventilation works by both actively exhausting polluted indoor air and actively drawing in fresh, outdoor air in a balanced, controlled ratio. Because a balanced system uses more fans and ducts than either the supply or exhaust approaches, the price tag is higher. However, balanced ventilation is appropriate for all climate zones and will deliver the best indoor air quality.

Employing a balanced approach with an energy recovery ventilator (ERV); incoming air can be conditioned and dehumidified, saving on heating and cooling expenses, while simultaneously improving indoor air quality.

Mechanical ventilation can take the benefits of a healthy home one step further by providing a controlled source of treated fresh air that balances indoor air quality with energy savings. This is more prevalent in today’s newer, tightly-built energy efficient homes. Your new home may look beautiful from the outside, but without a proper ventilation system installed by a professional HVAC contractor, invisible dangers lurk inside.