Codes Requiring Makeup Air & EPA Report
I. Current IRC and IECC codes require makeup air in residences that have a range hood exhaust fan capable of 400 cfm or larger. Minnesota code requires makeup air for 300 cfm or larger exhaust hoods.
II. IMC 505.2 Makeup air required.
Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute shall be provided with makeup air at a rate approximately equal to exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.
III. Excerpts from: Building Codes and Indoor Air Quality
Prepared for: U.S. Environmental Protection Agency, Indoor Environments Division
There are two indoor air quality related concerns with tightening the building envelope:
(1) a tight home may not provide sufficient outdoor air ventilation to dilute indoor-generated contaminants, and
(2) a tight home may be incapable of providing make up air for exhaust fans, a clothes dryer and vented combustion equipment. The negative pressure in the home caused by these appliances can draw exhaust gasses back into the home (backdrafting), and also force air through the building envelope and create moisture/mold problems as humid air condenses within the building envelope.
Whole house ventilation can be exhaust, supply, or balanced design. The exhaust design depressurizes the home and exacerbates problems associated with infiltration of hot humid air in warm climates and with backdrafting, while supply based systems pressurize homes and causes similar problems in cold climates.
These issues are addressed in ASHRAE Standard 62.2-2010. Balanced systems avoid these problems but are more expensive.
ASHRAE standard 62.2-2010 limits the capacity of a home’s two largest exhaust fans to a net total exhaust flow of 15 cfm/100 ft 2 when atmospherically-vented fuel burning appliances are located inside the pressure boundary, beyond which “compensating outdoor air” must be provided. ASHRAE is not specific as to how that compensating air is to be supplied. Since it does not take much negative pressure in a home to cause backdrafting, and since ASHRAE only requires compensating air based on the two largest exhaust systems, some uncertainty remains as to the backdrafting potential in some homes. Whole-house exhaust ventilation and other exhaust systems have the potential to cause significant depressurization.
The balanced design above occurs when an inexpensive FresherVent is added.
Midwestern states that have adopted the ASHRAE standard building code include: Minnesota, Iowa, Wisconsin, Nebraska, Illinois, Indiana, Ohio, Michigan.
I. Current IRC and IECC codes require makeup air in residences that have a range hood exhaust fan capable of 400 cfm or larger. Minnesota code requires makeup air for 300 cfm or larger exhaust hoods.
II. IMC 505.2 Makeup air required.
Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute shall be provided with makeup air at a rate approximately equal to exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.
III. Excerpts from: Building Codes and Indoor Air Quality
Prepared for: U.S. Environmental Protection Agency, Indoor Environments Division
There are two indoor air quality related concerns with tightening the building envelope:
(1) a tight home may not provide sufficient outdoor air ventilation to dilute indoor-generated contaminants, and
(2) a tight home may be incapable of providing make up air for exhaust fans, a clothes dryer and vented combustion equipment. The negative pressure in the home caused by these appliances can draw exhaust gasses back into the home (backdrafting), and also force air through the building envelope and create moisture/mold problems as humid air condenses within the building envelope.
Whole house ventilation can be exhaust, supply, or balanced design. The exhaust design depressurizes the home and exacerbates problems associated with infiltration of hot humid air in warm climates and with backdrafting, while supply based systems pressurize homes and causes similar problems in cold climates.
These issues are addressed in ASHRAE Standard 62.2-2010. Balanced systems avoid these problems but are more expensive.
ASHRAE standard 62.2-2010 limits the capacity of a home’s two largest exhaust fans to a net total exhaust flow of 15 cfm/100 ft 2 when atmospherically-vented fuel burning appliances are located inside the pressure boundary, beyond which “compensating outdoor air” must be provided. ASHRAE is not specific as to how that compensating air is to be supplied. Since it does not take much negative pressure in a home to cause backdrafting, and since ASHRAE only requires compensating air based on the two largest exhaust systems, some uncertainty remains as to the backdrafting potential in some homes. Whole-house exhaust ventilation and other exhaust systems have the potential to cause significant depressurization.
The balanced design above occurs when an inexpensive FresherVent is added.
Midwestern states that have adopted the ASHRAE standard building code include: Minnesota, Iowa, Wisconsin, Nebraska, Illinois, Indiana, Ohio, Michigan.