Ventilation Buying Guide
A quick guide to strategic product selection
Background
If you do not have a mechanical ventilation system in your home, the volume of fresh air that enters your home is just a matter of chance. As we all make improvements to increase the efficiency of heating and cooling our homes through weatherization, we tighten the thermal envelope and lessen the amount of air infiltration and/or leakage. While this improved energy efficiency is good for the environment and for your utility bills, it can have negative effects on indoor air quality and effectively, your health.
► Please note that we are not ventilation experts. The information provided below is for educational purposes only. Please consult with a certified HVAC specialist before selecting and installing a ventilation system.
Effects of poor ventilation
- Biological pollutants such as mold and mildew grow exponentially and can lead to asthma and other respiratory conditions. Excess pollutants are not only detrimental to your health, but can also lead to the deterioration of structure supports and walls.
- Volatile organic compounds (VOCs) are gases released from building materials, paints, carpets, furniture and plastics in your home. The U.S. EPA states that “at present, not much is known about what health effects occur from the levels of organics usually found in homes. Many organic compounds are known to cause cancer in animals; some are suspected of causing, or are known to cause, cancer in humans.”
- Toxic chemicals are likely leaking into your home from your attached garage. If you have an attached garage where your car is parked, along with the lawn mower, gas can and cleaning supplies, these fumes are likely leaking into your living space.
- Depressurization occurs when more air is exhausted by your bathroom fan, utility fan and kitchen range hood than can leak into your home, resulting in lower air pressure, which can cause a release of toxic gases from your home's combustion appliances. This condition can lead to carbon monoxide poisoning and fire.
Ventilation solutions
Ventilation systems provide fresh air to improve living conditions and prevent the potentially dangerous air quality conditions described above. When purchasing ventilation products, look for the ENERGY STAR label and always consult with a certified professional before installation. ENERGY STAR fans provide better efficiency and comfort with less noise, and use high performance motors that work better and last longer than motors used in conventional models.
Multi-port supply ventilation systems
To supply fresh air into the home using positive pressurization, an automatic multi-port supply ventilation system is a good choice. Ensure that the system you choose consists of a quiet, efficient supply fan with a MERV 13 filter; and quiet (less than 1 sone), ENERGY STAR qualified, automatic exhaust spot fans located in pollutant-prone, high-moisture locations such as the bathroom(s), kitchen(s) and utility room(s).
Supply ducts should reach at least four high-use locations in the home and ducting must be sealed. The supply fan should be located where air contamination from pollutants is least likely to occur (e.g. not near garage, driveway, dryer vents, etc.) but in an area where the lengths of duct work is minimal (closest to bedrooms and living rooms). In addition, carbon monoxide alarms must be placed throughout the home between 3 and 6 feet above the floor.
PROS
- Continuously provides fresh outdoor air to multiple locations of home (stale air should exit naturally)
- Relatively simple and inexpensive to install
- Prevents the entry of pollutants entering into the living space with high efficiency filters
- Prevents back-drafting of combustion gases from fireplaces and appliances (using positive pressure)
- Avoids pulling hot, humid air into wall cavities where condensation problems could occur (using positive pressure)
- Requires minimal ducting (in comparison to a balanced exhaust/supply system)
- Ideal for moderate climates
CONS
- Does not heat outdoor air before it enters the house, which may contribute to higher heating costs (compared with a heat recovery ventilation system – see below – that “treats” outdoor air before it enters the house to prevent extra energy use of the heating system)
- Stale indoor air is removed via kitchen, bathroom and utility room spot exhaust fans (exhaust of indoor air is not mechanically “guaranteed” however)
Balanced ventilation systems with Heat Recovery Ventilator (HRV)
To ensure that an equal amount of fresh outdoor air and stale indoor air are exchanged to and from the home, a balanced ventilation system with a heat recovery ventilator (HRV) and high efficiency filter (MERV 13) is a good choice. Balanced ventilation systems neither pressurize nor depressurize a house but rather introduce and exhaust approximately equal quantities of fresh outside air and polluted inside air. Meanwhile, a heat recovery ventilator (HRV) provides an energy efficient and effective ventilation system by transferring “waste heat” in the exhaust air stream into the incoming air stream, significantly reducing the energy required to heat cold outdoor air to interior comfort levels. An HRV is able to recover 60% - 80% of the heat energy that would otherwise be lost through ventilation. Even in mild climates, these energy savings have the potential to pay for the HRV before the equipment reaches its rated service life. Ducting for this system must be insulated and sealed.
PROS
- Continuously provides fresh outdoor air into multiple locations of home and ensures that stale exhaust air leaves the home in equal quantities
- Saves energy and reduces utility expense by recovering heat from conditioned exhaust air (courtesy of the HRV)
- Appropriate for all climates
CONS
- Relatively expensive
- More complex and difficult to install; requires more ducting (exhaust and supply)
- The cost of the additional electricity consumed by HRV system fans may exceed the energy savings from not having to condition the supply air
- Balance between exhaust and supply air can be difficult to maintain (can be thrown off by someone simply closing a door between a supply and pickup)
- Must be maintained more regularly than a supply ventilation system to prevent deterioration of ventilation rates and heat recovery, and to prevent mold and bacteria on heat exchanger surfaces
Exhaust fans
Exhaust fans are typically installed in bathrooms, utility rooms and kitchens. They remove stale air from the interior of your home and rely on natural air infiltration for air replacement (exhaust fans do not provide fresh air input).
When selecting an exhaust fan, it is important to consider size. Sizing is measured in air changes per hour (ACH), or how many times all the air in a specific room can be completely replaced per hour. The Home Ventilation Institute recommends the following:
- 8 ACH for bathrooms
- 15 ACH for kitchens
- 6 ACH for rooms other than bath and kitchen
Please note that your local building code and local regulations may differ from the above sizing recommendations. To identify the specific sizing requirements for your bathroom, calculate the air volume of your bathroom (height, length, width). Since the recommended ACH for bathrooms is 8 ACH, you multiply the cubic feet of your bathroom by 8, which equals the cubic feet of air that must be changed per hour. Exhaust fan ratings are per minute, so divide this number by 60 to get the proper fan size in cubic feet per minute (CFM).
Example:
Room Dimensions 10 x 5 x 8 = 400 cubic feet
400 x 8 = 3200 cubic feet of air that must be changed per hour
3200/60 = 53 CFM sized fan
PROS
- Relatively simple and inexpensive to install
- Effective at removing stale, moist air
CONS
- Does not provide fresh air input
- Depressurization can occur if your thermal envelope does not allow adequate fresh air to naturally fill or replace the removed air
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