Whole-House Balanced Ventilation Systems

Written by The U.S. Department of Energy's Office of EERE
Sat, Mar 06, 2010

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Balanced ventilation systems, if properly designed and installed, neither pressurize nor depressurize a house. Rather, they introduce and exhaust approximately equal quantities of fresh outside air and polluted inside air, respectively.

Diagram of a balanced ventilation system, showing a side view of a simple house with an attic, living space, and basement. In the attic is horizontal duct work (labeled room air exhaust ducts) leading from an exhaust fan into the living space rooms. A pipe extending vertically from the exhaust fan and through the roof is labeled the exhaust air outlet. A box in the basement (labeled the supply fan) has two ducts leading into the living space and one duct leading to the outside, labeled the fresh air inlet. Arrows show air flow into the house through the fresh air inlet in the basement, moving through the supply fan into the living space, through the room air exhaust ducts, into the exhaust fan in the attic, and out of the house through the exhaust air outlet in the roof.

A balanced ventilation system usually has two fans and two duct systems. It facilitates good distribution of fresh air by placing supply and exhaust vents in appropriate places. Fresh air supply and exhaust vents can be installed in every room. But a typical balanced ventilation system is designed to supply fresh air to bedrooms and living rooms where people spend the most time. It also exhausts air from rooms where moisture and pollutants are most often generated (kitchen, bathrooms, and perhaps the laundry room). Some designs may use a single-point exhaust. Because they directly supply outside air, balanced systems allow the use of filters to remove dust and pollen from outside air before introducing it into the house.

Balanced ventilation systems are appropriate for all climates. However, because they require two duct and fan systems, balanced ventilation systems are usually more expensive to install and operate than supply or exhaust systems.

Like both supply and exhaust systems, balanced ventilation systems do not temper or remove moisture from the make-up air before it enters the house. Therefore, they may contribute to higher heating and cooling costs, unlike energy recovery ventilation systems. Also, like supply ventilation systems, outdoor air may need to be mixed with indoor air before delivery to avoid cold air drafts in the winter.

Article source: The U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE). For the most up-to-date information please visit the EERE website.