How To Use the Test
Using the previous examples, if the measured airflow from a forced-air register is less than 10 L/s, the furnace is delivering only a small amount of heat to a room.
If you install a 100 cfm exhaust fan, and the fan inflates a standard bag in less than two seconds, you have the rated exhaust flow for the fan.
Garbage Bag Airflow Test is also useful if you have changed your heating or cooling systems, or if you have made major renovations to your house.
Table 1 Small garbage bag (66 x 91 cm [26 x 36 in.])
Time to inflate* Flow of air into the bag
2 seconds 35 L/s (75 cfm)
4 seconds 20 L/s (40 cfm)
10 seconds 10 L/s (20 cfm)
L/s = litres per second; cfm = cubic feet per minute
- For deflation, add a second. Therefore, 35 L/s would take about three seconds and 20 L/s about five seconds.
Table 2 Big garbage bag (79 x 119 cm [31 x 47 in.])
Time to inflate* Flow of air into the bag
2 seconds 100 L/s (210 cfm)
4 seconds 50 L/s (105 cfm)
6 seconds 35 L/s (75 cfm)
10 seconds 20 L/s (40 cfm)
L/s = litres per second; cfm = cubic feet per minute
- Deflation times are about the same as inflation times.