ASHRAE 62.2 is a minimum national standard that provides methods for achieving acceptable indoor air quality in typical residences. It was developed and is maintained by the American Society of Heating and Air-Conditioning Engineers (ASHRAE). The standard has three main components:

  • Whole House Ventilation: Exhausting stale indoor air and replacing it with fresh outdoor air.
  • Local Exhaust: Exhausting high levels of contaminates and moisture typically associated with cooking, bathrooms, etc.
  • Source Control: Preventing outside contaminates from entering the home – storing paint, gasoline, etc. inside the home.

The recommendations that follow are for most common conditions, extreme conditions require additional consideration.

Whole House Ventilation

The exhaust fan dilutes the air in the main living spaces with outside air to remove unavoidable contaminants from people, pets, cleaning, off-gassing, etc. The whole house fan flow rate is determined based on the floor space and the number of bedrooms. The whole house fan provides multiple air exchanges within the home each day. The operation can be continuous or intermittent (much higher airflow cycled by a timer) if 1 sone or less. The formula for calculating how much ventilation is required is:
(total square footage of the home/100) + ((number of bedrooms+1) x 7.5 cfm)

Okay, So What Am I Looking For In A Whole House Fan?

The key with a Whole House Exhaust Fan is quiet. In most cases the exhaust fan will be located in a central location of the home and will run continuously, so you want it to be quiet. ASHRAE 62.2 calls for continuously running exhaust fan to have a sound rating of 1.0 sones or less. The reason being, if the fan is too loud, the homeowners will be tempted to turn it off – negating the whole reason why it is installed.

Whole House Ventilation – Range Hoods

We offers multiple ways to solve for whole house ventilation. The best option is using the range hood as both the continuous ventilation and local exhaust solution. The kitchen is generally located in a central location of the home without any barriers that would prevent a free flow of air to the rest of the house (typically there isn’t a door that blocks the air flow like you would have in a bathroom). By using a continuous operation range hood, it eliminates the need to install an additional whole house fan in another location. There are multiple range hood options that provide barely audible continuous whole house ventilation on low speed while effectively clearing the air on the normal operating and high speeds. They can be set on-site to the specific ventilation need of the home, ensuring the residence will pass a blower door test if done. All ASHRAE 62.2 range hoods are ENERGY STAR® qualified.

Whole House Ventilation – Exhaust Fans

If a range hood is not a suitable solution, the whole house ventilation can be solved using a ceiling mounted exhaust fan. Again, there are has multiple models to choose from. We suggest using a variable speed model that can be adjusted on site. This ensures that if a blower door test is done on the home, the fan can be adjusted to meet the specific ventilation need without having to re-install a larger or smaller fan.

Local Exhaust

Local Exhaust removes high concentrations of contaminants in the rooms where they occur (kitchens and bathrooms). To comply with ASHRAE 62.2, exhaust fans must operate at a certified sound level of 3.0 sones or less. As with the whole house fans, this ensure that the exhaust fan will actually be utilized, eliminating the excuse that it is too loud. The fan must also be sized to effectively exhaust the area. For bathrooms, the general rule is 1 CFM per square foot with a minimum of 50 CFM. In kitchens, a minimum of 100 CFM is required. Depending on the size and type of range in the kitchen, additional CFM my be required. Always check your local codes before installing any ventilation equipment. All ENERGY STAR qualified exhaust fans can be used for local exhaust. For the lowest cost and quickest installation ENERGY STAR qualified exhaust fan on the market today. A great upgrade is to install an automated ventilation product that feature motion sensors, humidity sensors or both. Automated ventilation ensures that the fan is being utilized (does not require the residents to turn the fan on or off) and simplifies the process.

Source Control

Many indoor air quality problems can be avoided by limiting the introduction of items with the potential for creating problems such as high VOC adhesives. Ventilation is not intended to overcome obvious defects such as a leaky basement, proper repairs are required.

Fan Duct Work

We recommends designers follow the prescriptive duct sizing recommendations in ASHRAE 62.2. This results in lower energy usage due to low resistance to flow and strong likelihood that installed performance will match design. Note that 3″ duct work is almost never suitable by these recommendations. There are several new products with larger diameter duct connections (50 cfm 4″ duct, 80 cfm 6″ duct) to make compliance easy.

More Resources

Many other details for proper design regarding solid fuel appliances, dryer exhaust, filters, air intakes, instructions for occupants, etc. can be found in section 6, refer to ASHRAE std 62.2 for additional guidance

NOTE: The recommendations made here cover the most common situations and in our opinion represent the best way to meet the intent of the standard, derive the greatest benefit and also balance cost, complexity, operational simplicity, ease of installation and other factors. The ASHRAE Standard provides many other possibilities as well as specific exceptions that might apply to your situation (extreme cold, extreme humidity, etc.). If you have reason to suspect that your situation is outside the norm (steam sauna, indoor pool, high occupancy, etc.) refer to ASHRAE 62.2 for additional information or consult a professional for help.