|DRYER EXHAUST DUCT FITTING TYPE||EQUIVALENT LENGTH|
|4-inch radius mitered 45-degree elbow||2 feet 6 inches|
|4-inch radius mitered 90-degree elbow||5 feet|
|6-inch radius smooth 45-degree elbow||1 foot|
|6-inch radius smooth 90-degree elbow||1 foot 9 inches|
|8-inch radius smooth 45-degree elbow||1 foot|
|8-inch radius smooth 90-degree elbow||1 foot 7 inches|
|10-inch radius smooth 45-degree elbow||9 inches|
|10-inch radius smooth 90-degree elbow||1 foot 6 inches|
- The fan for overhead range hoods and downdraft exhaust equipment not integral with the cooking appliance shall be listed and labeled in accordance with UL 507.
- Overhead range hoods and downdraft exhaust equipment with integral fans shall comply with UL 507.
- Domestic cooking appliances with integral downdraft exhaust equipment shall be listed and labeled in accordance with ANSI Z21.1 or UL 858.
- Microwave ovens with integral exhaust for installation over the cooking surface shall be listed and labeled in accordance with UL 923.
- The duct is installed under a concrete slab poured on grade.
- The underfloor trench in which the duct is installed is completely backfilled with sand or gravel.
- The PVC duct extends not more than 1 inch (25 mm) above the indoor concrete floor surface.
- The PVC duct extends not more than 1 inch (25 mm) above grade outside of the building.
- The PVC ducts are solvent cemented.
|DUCT TYPE||FLEX DUCT||SMOOTH-WALL DUCT|
|Fan airflow rating (CFM @ 0.25 inch wca)||50||80||100||125||150||200||250||300||50||80||100||125||150||200||250||300|
|Diameterb (inches)||Maximum lengthc, d, e
|8 and above||NL||NL||NL||NL||NL||189||111||69||NL||NL||NL||NL||NL||NL||198||133|
- Fan airflow rating shall be in acordance with ANSI/AMCA 210-ANSI/ASHRAE 51.
- For noncircular ducts, calculate the diameter as four times the cross-sectional area divided by the perimeter.
- This table assumes that elbows are not used. Fifteen feet of allowable duct length shall be deducted for each elbow installed in the duct run.
- NL = no limit on duct length of this size.
- X = not allowed. Any length of duct of this size with assumed turns and fittings will exceed the rated pressure drop.
- Not less than 3 feet (914 mm) from property lines.
- Not less than 3 feet (914 mm) from gravity air intake openings, operable windows and doors.
- Not less than 10 feet (3048 mm) from mechanical air intake openings except where the exhaust opening is located not less than 3 feet (914 mm) above the air intake opening. Openings shall comply with Sections R303.5.2 and R303.6.
Ventilation rate credit. The minimum mechanical ventilation rate determined in accordance with Table M1505.4.3(1) or Equation 15-1 shall be reduced by 30 percent, provided that both of the following conditions apply:
- Programmed intermittent operation. The whole-house mechanical ventilation system is permitted to operate intermittently where the system has controls that enable operation for not less than 25 percent of each 4-hour segment and the ventilation rate prescribed in Table M1505.4.3(1), by Equation 15-1 or by Exception 1 is multiplied by the factor determined in accordance with Table M1505.4.3(2).
|DWELLING UNIT FLOOR AREA (square feet)||NUMBER OF BEDROOMS|
|Airflow in CFM|
|RUN-TIME PERCENTAGE IN EACH 4-HOUR SEGMENT||25%||33%||50%||66%||75%||100%|
- For ventilation system run-time values between those given, the factors are permitted to be determined by interpolation.
- Extrapolation beyond the table is prohibited.
ONE- AND TWO-FAMILY DWELLINGS
|AREA TO BE EXHAUSTED||EXHAUST RATESa|
|Kitchens||100 cfm intermittent or 25 cfm continuous|
|Bathrooms-Toilet Rooms||Mechanical exhaust capacity of 50 cfm intermittent or 20 cfm continuous|
- The listed exhaust rate for bathrooms-toilet rooms shall equal or exceed the exhaust rate at a minimum static pressure of 0.25 inch water column in accordance with Section M1505.3.