Best home ventilation Systems

July 25, 2017
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Best Home Ventilation Systems

Diagram of an exhaust ventilation system, showing a side view of a simple house with an attic, living space, and basement. In the attic is horizontal duct work leading into a box labeled the central exhaust fan. A duct extending vertically from the central exhaust fan and through the roof is labeled the exhaust air outlet. Arrows show air flow going into the house through vents in the walls, moving through the living space, and moving into the central exhaust fan and out of the house through the exhaust air outlet. Minus symbols show that the living space has negative air pressure. Air infiltration into the living space through the attic, the basement, and the exterior walls is indicated by arrowsEnergy-efficient homes - both new and existing - require mechanical ventilation to maintain indoor air quality. There are four basic mechanical whole-house ventilation systems - exhaust, supply, balanced, and energy recovery.

Comparison of Whole-House Ventilation Systems

Ventilation System

Pros

Cons

Exhaust
  • Relatively inexpensive and simple to install
  • Work well in cold climates.
  • Can draw pollutants into living space
  • Not appropriate for hot humid climates
  • Rely in part on random air leakage
  • Can increase heating and cooling costs
  • May require mixing of outdoor and indoor air to avoid drafts in cold weather
  • Can cause backdrafting in combustion appliances.

Supply
  • Allow better control than exhaust systems
  • Minimize pollutants from outside living space
  • Prevent backdrafting of combustion gases from fireplaces and appliances
  • Allow filtering of pollen and dust in outdoor air
  • Allow dehumidification of outdoor air
  • Work well in hot or mixed climates.
  • Can cause moisture problems in cold climates
  • Will not temper or remove moisture from incoming air
  • May require mixing of outdoor and indoor air to avoid drafts in cold weather.

Balanced
  • Appropriate for all climates
  • Can cost more to install and operate than exhaust or supply systems
  • Can increase heating and cooling costs.

Energy Recovery & Heat Recovery Ventilators
  • Reduce heating and cooling costs
  • Available as both small wall- or window-mounted models or central ventilation systems
  • Cost-effective in climates with extreme winters or summers and high fuel costs.
  • Can cost more to install than other ventilation systems
  • May not be cost-effective in mild climates
  • May be difficult to find contractors with experience and expertise to install these systems
  • Require freeze and frost protection in cold climates
  • Require more maintenance than other ventilation systems.

Exhaust Ventilation Systems

Exhaust ventilation systems work by depressurizing your home. The system exhausts air from the house while make-up air infiltrates through leaks in the building shell and through intentional, passive vents.

Exhaust ventilation systems are most appropriate for cold climates. In climates with warm humid summers, depressurization can draw moist air into building wall cavities, where it may condense and cause moisture damage.

Exhaust ventilation systems are relatively simple and inexpensive to install. Typically, an exhaust ventilation system consists of a single fan connected to a centrally located, single exhaust point in the house. A better design is to connect the fan to ducts from several rooms, preferably rooms where pollutants are generated, such as bathrooms. Adjustable, passive vents through windows or walls can be installed in other rooms to introduce fresh air rather than rely on leaks in the building envelope. Passive vents may, however, require larger pressure differences than those induced by the ventilation fan to work properly.

One concern with exhaust ventilation systems is that - along with fresh air - they may draw in pollutants, including:

  • Radon and molds from a crawlspace
  • Dust from an attic
  • Fumes from an attached garage
  • Flue gases from a fireplace or fossil-fuel-fired water heater and furnace.

These pollutants are a particular concern when bath fans, range fans, and clothes dryers (which also depressurize the home while they operate) are run when an exhaust ventilation system is also operating.

Exhaust ventilation systems can also contribute to higher heating and cooling costs compared with energy recovery ventilation systems because exhaust systems do not temper or remove moisture from the make-up air before it enters the house.

Supply Ventilation Systems

Supply ventilation systems use a fan to pressurize your home, forcing outside air into the building while air leaks out of the building through holes in the shell, bath, and range fan ducts, and intentional vents (if any exist).

Like exhaust ventilation systems, supply ventilation systems are relatively simple and inexpensive to install. A typical supply ventilation system has a fan and duct system that introduces fresh air into usually one - but preferably several - rooms that residents occupy most (e.g., bedrooms, living room). This system may include adjustable window or wall vents in other rooms.

Source: energy.gov
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