Outdoor Air Intakes Damper Controlled
In a home that has a balanced ventilation system that uses central-fan-integrated supply ventilation, a heat recovery ventilator (HRV), or an energy recovery ventilator (ERV), fresh air is brought into the home from a ventilation air inlet located on the exterior of the home (often in a roof soffit or porch roof, see the guide Ventilation Air Inlet Locations. If the outside air inlet is ducted to the return side of the central air handler, the duct should not be allowed to remain open at all times. Over-ventilation can unnecessarily increase energy use and can increase indoor humidity in humid climates. The volume and duration of fresh air intake periods should be controlled by a motorized damper installed within the duct that is controlled electronically to automatically provide intermittent fresh air based on a timer. This timer should be set by the HVAC installer to meet desired or code-mandated ventilation requirements (for example, the ventilation minimum determined using ASHRAE Standard 62.2-2010/2013, Ventilation for Acceptable Indoor Air Quality in Low-Rise Residential Buildings). See manufacturers’ instructions for installing and setting the timer, damper, and controls.
The timer can be used to coordinate periods of fresh air intake with operation of an exhaust fan within the home to provide balanced ventilation, so that the home does not become overpressurized. For more information, see the guide Whole-Building Delivered Ventilation.
The electronic controls can also be set to coordinate operation with the central air handler fan by cutting back on fan-only run time during hours when the desired amount of ventilation run time is met by the HVAC fan while it is operating to meet heating or cooling demand. See the guide ECM Air Handler Fans.
Figure 1 shows a central-fan-integrated ventilation system with a fresh air intake that is ducted directly to the return side of the air handler. Electronic controls operate the motorized damper to balance the amount of air brought into the home through the fresh air intake with exhaust fans to provide adequate ventilation air to meet the requirements of ASHRAE 62.2.
Figure 1 – A fresh air inlet is ducted to the return side of the home’s central air handler; a motorized damper and electronic controls help balance the flow of fresh incoming air with controlled exhaust to meet ventilation requirements
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References and Resources
Compliance
ASHRAE 62.2-10/13
The standard "Ventilation for Acceptable Indoor Air Quality in Low-Rise Residential Buildings" by the American Society of Heating, Air-Conditioning and Refrigeration Engineers (ASHRAE), defines methods for determining the minimum levels of ventilation needed to provide acceptable indoor air quality in low-rise residential buildings.
2009 IECC
Section 403.5 Mechanical ventilation (Mandatory). Automatic or gravity dampers are installed on all outdoor air intakes and exhausts.
Section R403.5 Mechanical ventilation (Mandatory). The building must have ventilation that complies with the International Residential Code or International Mechanical Code. Outdoor air intakes and exhausts must have automatic or gravity dampers that close when the ventilation system is not operating.
Section R403.5.1 Whole-House mechanical ventilation system fan efficacy. Mechanical ventilation system fans should meet the fan efficacy requirements shown in IECC Table R403.5.1. However, when the HVAC air handler or furnace blower fan is used for ventilation, it should be powered by an electronically commutated motor.
Section R403.6 Mechanical ventilation (Mandatory). The building must have ventilation that complies with the International Residential Code or International Mechanical Code. Outdoor air intakes and exhausts must have automatic or gravity dampers that close when the ventilation system is not operating.
Section R403.6.1 Whole-House mechanical ventilation system fan efficacy. Mechanical ventilation system fans should meet the fan efficacy requirements shown in IECC Table R403.6.1. However, when the HVAC air handler or furnace blower fan is used for ventilation, it should be powered by an electronically commutated motor.
ENERGY STAR Certified Homes (Version 3.0, Revision 08), Rater Field Checklist, 7. Whole-House Mechanical Ventilation System, 7.3. No outdoor air intakes connected to return side of the HVAC system, unless controls are installed to operate intermittently and automatically based on a timer and to restrict intake when not in use (e.g., motorized damper).
The U.S. Department of Energy (DOE) Zero Energy Ready Home National Program Requirements requires (in Exhibit 1 and 6) that all homes meet ENERGY STAR Certified Homes Version 3 or 3.1 and the U.S. Environmental Protection Agency Indoor airPLUS Construction Specifications
The U.S. Environmental Protection Agency (EPA) Indoor airPLUS Construction Specifications requires homes to meet the ENERGY STAR Certified Homes requirements. Additional advisories include the following.
4.5 Mechanical Whole-House Ventilation
Advisory: Outdoor air ducts connected to the return side of an air handler should be used as supply ventilation only if the manufacturers’ requirements for return air temperature are met (e.g., most manufacturers recommend a minimum of 60 degrees Fahrenheit air flow across furnace heat exchangers).
The following Building America Teams contributed to the content in this Guide.
Pacific Northwest National Laboratory