For the airflow velocities required to activate the switch for any given duct size with horizontal or vertical upward flow, see the following table based on a standard air density of 0.075 lb/ft3 (1.2 kg/m3).
| Paddle width | Switch actuation on flow | Minimum air velocity required to activate control, fpm (m/s) | |||
|---|---|---|---|---|---|
| Horizontal flow | Vertical flow | ||||
| 50 in.2 (323 cm2) or larger duct area | Less than 50 in.2 (323 cm2) duct area | 50 in.2 (323 cm2) or larger duct area | Less than 50 in.2 (323 cm2) duct area | ||
| 2-1/8 in. | Increase R to Y closes |
625 (3.2) | 575 (2.9) | 950 (4.8) | 750 (3.8) |
| Decrease R to B closes |
325 (1.7) | 220 (1.1) | 850 (4.3) | 575 (2.9) | |
| 3-1/8 in. | Increase R to Y closes |
500 (2.5) | 350 (1.8) | 750 (3.8) | 500 (2.5) |
| Decrease R to B closes |
250 (1.3) | 100 (0.5) | 650 (3.3) | 350 (1.8) | |