EXCEPTIONS: | 1. Hospital, vivarium and laboratory systems that utilize flow control devices on exhaust or return to maintain space pressure relationships necessary for occupant health and safety or environmental control shall be permitted to use variable volume fan power limitation. |
2. Individual exhaust fans with motor nameplate horsepower of 1 hp or less are exempt from allowable fan motor horsepower requirements. |
Limit | Constant Volume | Variable Volume | |
Option 1: Fan system motor nameplate hp | Allowable nameplate motor hp | hp ≤ CFMS × 0.0011 | hp ≤ CFMS × 0.0015 |
Option 2: Fan system bhp | Allowable fan system bhp | bhp ≤ CFMS × 0.00094 + A | bhp ≤ CFMS × 0.0013 + A |
For SI: | 1 cfm = 0.471 L/s. 1 bhp = 735.5 W, 1 hp = 745.5 W. | |
Where: | ||
CFMS | = | The maximum design supply airflow rate to conditioned spaces served by the system in cubic feet per minute. |
hp | = | The maximum combined motor nameplate horsepower. |
bhp | = | The maximum combined fan brake horsepower. |
A | = | Sum of [PD × CFMD/4131] |
Where: | ||
PD | = | Each applicable pressure drop adjustment from Table C403.8.1(2) in. w.c. |
CFMD | = | The design airflow through each applicable device from Table C403.8.1(2) in cubic feet per minute. |
Device | Adjustment |
Credits | |
Return air or exhaust system required by code or accreditation standards to be fully ducted, or systems required to maintain air pressure differentials between adjacent rooms | 0.5 inch w.c. (2.15 inches w.c. for laboratory and vivarium systems) |
Return and/or exhaust air flow control devices | 0.5 inch w.c. |
Exhaust filters, scrubbers, or other exhaust treatment | The pressure drop of device calculated at fan system design condition |
Particulate filtration credit: MERV 9 - 12 | 0.5 inch w.c. |
Particulate filtration credit: MERV 13 - 15 | 0.9 inch w.c. |
Particulate filtration credit: MERV 16 and greater and electronically enhanced filters | Pressure drop calculated at 2x clean filter pressure drop at fan system design condition |
Carbon and other gas-phase air cleaners | Clean filter pressure drop at fan system design condition |
Biosafety cabinet | Pressure drop of device at fan system design condition |
Energy recovery device, other than coil runaround loop | For each airstream (2.2 × energy recovery effectiveness – 0.5) inch w.c. |
Coil runaround loop | 0.6 inch w.c. for each airstream |
Evaporative humidifier/cooler in series with another cooling coil | Pressure drop of device at fan system design conditions |
Sound attenuation section (fans serving spaces with design background noise goals below NC35) | 0.15 inch w.c. |
Exhaust system serving fume hoods | 0.35 inch w.c. |
Laboratory and vivarium exhaust systems in high-rise buildings | 0.25 inch w.c./100 feet of vertical duct exceeding 75 feet |
Deductions | |
Systems without central cooling device | -0.6 inch w.c |
Systems without central heating device | -0.3 inch w.c. |
Systems with central electric resistance heat | -0.2 inch w.c. |
For SI: | 1 inch w.c. = 249 Pa, 1 inch = 25.4 mm. |
w.c. = water column. |
EXCEPTIONS: | 1. For fans less than 6 bhp (4413 W), where the first available motor larger than the brake horsepower has a nameplate rating within 50 percent of the bhp, selection of the next larger nameplate motor size is allowed. |
2. For fans 6 bhp (4413 W) and larger, where the first available motor larger than the bhp has a nameplate rating within 30 percent of the bhp, selection of the next larger nameplate motor size is allowed. | |
3. For fans used only in approved life safety applications such as smoke evacuation. | |
4. Fans with motor nameplate horsepower less than 1 hp are exempt from this section. |
EXCEPTION: | The following fans are not required to have a fan efficiency grade: |
1. Individual fans with a motor nameplate horsepower of 5 hp (3.7 kW) or less that are not part of a group operated as the functional equivalent of a single fan. | |
2. Multiple fans in series or parallel that have a combined motor nameplate horsepower of 5 hp (3.7 kW) or less and are operated as the functional equivalent of a single fan. | |
3. Fans that are part of equipment covered under Section C403.3.2. | |
4. Fans included in an equipment package certified by an approved agency for air or energy performance. | |
5. Powered wall/roof ventilators. | |
6. Fans outside the scope of AMCA 205. | |
7. Fans that are intended to operate only during emergency conditions. |
EXCEPTIONS: | 1. Group R heat recovery ventilator and energy recovery ventilator fans that are less than 400 cfm. |
2. Where whole house ventilation fans are integrated with forced-air systems that are tested and listed HVAC equipment, provided they are powered by an electronically commutated motor where required by Section C405.8. | |
3. Domestic clothes dryer booster fans, domestic range hood exhaust fans, and domestic range booster fans that operate intermittently. |
Fan Location | Air Flow Rate Minimum (cfm) | Minimum Efficacy (cfm/watt) | Air Flow Rate Maximum (cfm) |
Exhaust fan: Bathroom, utility room, whole house | 10 | 2.8 | < 90 |
Exhaust fan: Bathroom, utility room, whole house | 90 | 3.5 | Any |
In-line (single-port and multi-port) fans | Any | 3.8 | Any |
EXCEPTIONS: | 1. Modulating fan control is not required for chilled water and evaporative cooling units with fan motors of less than 1 hp (0.746 kW) where the units are not used to provide ventilation air and the indoor fan cycles with the load. |
2. Where the volume of outdoor air required to comply with the ventilation requirements of the International Mechanical Code at low speed exceeds the air that would be delivered at the minimum speed defined in Section C403.8.5, the minimum speed shall be selected to provide the required ventilation air. |
Cooling System Type | Fan Motor Size | Mechanical Cooling Capacity |
DX cooling | Any | ≥ 42,000 Btu/h |
Chilled water and evaporative cooling | ≥ 1/4 hp | Any |