ASHRAE Residential Ventilation Standard Approved
Since the oil shortages 30 years ago, U.S. homes have become more energy efficient thanks to a variety of developments, including better sealing to prevent loss of interior conditioned air. With the rise in well-sealed, energy-efficient homes has come an increased interest in maintaining high indoor-air quality.
To address indoor air-quality issues, the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has approved and published the first nationally recognized indoor air-quality standard developed solely for homes. Standard 62.2, Ventilation and Acceptable Indoor Air Quality in Low-rise Residential Buildings, was approved in July 2003 after six years of work by building scientists and engineers.
The standard went through several revisions and was the subject of significant controversy, as well as appeals after its approval. One of the first hurdles was convincing building professionals that a standard was needed for residential construction; a commonly held belief was windows and relatively leaky building envelopes provide sufficient ventilation in homes.
However, research shows that pollutant concentrations in indoor air can be two to five times greater than in outdoor air. Because most people spend 90 percent of their time indoors and a substantial portion of this time in their homes, the ASHRAE standard was developed to ensure healthy indoor air in residences.
Goals of Standard 62.2
The most effective strategy for minimizing indoor exposure to pollutants is to prevent them from being released into the air in the first place. To this end, the standard requires source-control measures that exhaust pollutants (e.g. from combustion appliances, cooking fumes, see Figure 1) from specific rooms before the pollutants enter the rest of the household. In addition, whole-house ventilation brings fresh air into the house, diluting pollutants that are difficult to control at the source.
What 62.2 Covers
Standard 62.2 addresses three primary areas:
- Whole-house ventilation
- Local exhaust
- Source control
Whole-house ventilation. The whole-house ventilation requirements in the standard are intended to dilute contaminant emissions from people, materials, and background processes.
In typical houses, the standard requires a ventilation rate of about 50 cubic feet per minute (cfm) or 25 liters per second (L/s); larger houses must have a higher rate. Almost all houses must have a whole-house mechanical ventilation system rated at 7.5 cfm per occupant, plus one cfm for every 100 square feet of floor area that can be occupied. Houses exempt from this requirement include houses in hot climates without air conditioning, houses conditioned for less than 876 hours per year (e.g., cabins and vacation homes that are occupied for brief periods), and houses in hot dry climates, primarily in the southeast and southwest U.S. where occupants generally ventilate by opening windows.
Local exhaust. The intent of the standard's local exhaust requirements is to remove contaminants from rooms such as kitchens and bathrooms that have specific pollutant sources (e.g., cooking, electrical equipment, moisture).
The standard requires a local mechanical exhaust system to be installed in each kitchen and bathroom. A user-operable vented range hood must exhaust at least 100 cfm (50 L/s) of air. The standard permits unducted range hoods only in kitchens with a mechanical exhaust system rated at five kitchen air changes per hour (continuous or intermittent). Bathrooms must have mechanical exhaust; the minimum requirement is a user-operable fan that exhausts at least 50 cfm (25 L/s). Mechanical exhaust is not required in toilets, laundry rooms, lavatories, and utility rooms.
Source control. This area of the standard addresses sources of contamination not covered in the first two areas.
Houses with appliances vented to the outside need to be tested for backdraft if the sum of the cfm ratings of the two largest exhaust fans is greater than 15 cfm per 100 square feet of habitable space. Air handlers located in garages must be tested for air tightness.
Secondary requirements address the properties of equipment used to meet the primary requirements, e.g., labeling, sound, and flow ratings for fans. Other requirements cover building design issues, for example avoiding ventilation design mistakes that depressurize the house and unintentionally draw contaminants from combustion appliances back into the house.
Recognizing the diversity of housing types and climates, the ASHRAE Standards Committee gave builders a flexible approach for meeting the standard. Each requirement can be met using different building methods and technologies.
Although the approval of the standard is a major step forward in creating consensus on how to maximize indoor air quality, work in this area is continuing. ASHRAE is preparing a User's Manual for Standard 62.2. (ASHRAE often prepares manuals for practitioners because the official language of a standard can be difficult to interpret; these manuals are often more important to practicing professionals than the standard itself because the manuals include design examples and advice about different approaches to meeting standard requirements).
ASHRAE Standard 62.2 is subject to continuous maintenance. Anyone can make proposals to change the standard, which can be modified as needs arise. The standard will also be on a regular schedule for consideration of changes submitted by the public. The project committee is currently considering several issues that could be addressed in addenda, including carbon monoxide alarms, garage ventilation, and testing and certification requirements.
The committee will also consider modifications to address some issues that were not resolved before the standard was published. These include variances for climate differences, exhaust requirements for laundries and toilets, air-distribution requirements, and air-cleaning options.
When Standard 62.2 became official, Standards Project Committee 62.2 was dissolved and a Standing Standards Project Committee (SSPC 62.2) took take over maintenance of the standard. Many of the members of SPC 62.2P became members of SSPC 62.2 to assure continuity, but SSPC 62.2 is larger than the committee that drafted the standard, which increases the number of interests and stakeholders who can participate.
Max Sherman, leader of the Environmental Energy Technologies Division's Energy Performance of Buildings Group, was the chair of SPC 62.2 and guided the committee from its inception in 1997 until publication of the standard. David Grimsrud, of the University of Minnesota, is now the chair of Standing Standards Project Committee 62.2. Grimsrud was leader of EETD's Indoor Air Quality program in the 1980s.
For more information, contact:
- Max Sherman
- (510) 486-4022; fax (510) 486-6641
Also, see: Sherman, M. 2004. ASHRAE's New Residential Ventilation Standard, ASHRAE Journal, January: S149-S156.
Standard 62.2 is available from http://ashrae.org/.
This work was funded by the U.S. Department of Energy's Office of Building Technology State and Community programs.