Who makes the rules?

| by Patrick Nielsen
Who makes the rules?

When we at Broan-NuTone design and market ventilation systems, one of our guiding factor is the ASHRAE 62.2 residential ventilation standard. It was developed and maintained by the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) over 20 years ago.

ASHRAE standards are commonly used as baselines for building codes and programs, so your local code may incorporate this standard. The goal of the ASHRAE 62.2 standard was to address concerns of increasing levels of indoor contaminants and mold growth in residential buildings.

Years of studies and input by building science experts and health professionals indicated a need for mechanical ventilation in homes to protect the health of occupants and the value of the building.

The two main requirements of ASHRAE 62.2 are:

  1. Whole house mechanical ventilation to maintain acceptable air quality, and
  2. Local exhaust fans in each kitchen and bathroom to reduce the levels of contaminants and moisture in these spaces. 

Whole House Mechanical Ventilation (WHMV)

Whole house mechanical ventilation maintains the overall indoor air quality of the home by moving air continuously, compared to local exhaust fans in kitchens and bathrooms that remove high volume and intensity of pollutants from rooms where they are created.

The amount of whole house mechanical ventilation required is determined using a formula that takes into consideration the size of the building and the potential number of occupants, resulting in a cubic feet per minute of air movement. Whole house mechanical ventilation can be accomplished using a single ventilation fan, air exchanger or other method; or use a combination of the same to achieve the required airflow.

Since the ventilation solution is running throughout the day, ASHRAE 62.2 requires that the ventilation solution have a sound level of 1 Sone or less. This is to avoid any occupant dissatisfaction or annoyance, which may cause them to turn off the ventilation system.

Local Exhaust

The standard also requires local exhaust in kitchens and bathrooms to remove high volume/intensity pollutants produced in those areas before they spread to the rest of the home.

The humidity, cooking by-products and odors produced in these spaces adversely affect the overall indoor air quality of the home. Ventilation fans for these spaces must have verified performance to make sure they are capable of accomplishing their task.

For bathrooms the fan must be capable of delivering a minimum of 50 CFM of exhaust ventilation when installed and for kitchens ventilation it is 100 CFM. 

ASHRAE provides a number of options to determine proper operation. The first is using the rated performance of the fan at .25 static pressure (Ps) tested per the standards of the Home Ventilating Institute (HVI).

Alternatively, the fan or range hood can be tested after installation using test equipment such as a “flow hood”. Some building codes and green building standards require the use of this method. Additionally as with whole house mechanical ventilation, there are sound requirements for local exhaust fans in the kitchen and bathroom. These fans must have a sound level no greater than 3 sones to not create occupant dissatisfaction.


Topics: Bathroom, Indoor Air Quality, Kitchen, Ventilation


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