Airbags in piggery ventilation (II)

Last month I outlined the usefulness of this under-recognised system. Here are some easy to follow principles. The airbag (i.e. the duct) diameter should match the diameter of the fan. Ordinary propeller fans are sufficient, but use the higher speeds available as this ensures firm inflation and a good throw of air. Use heavy gauge polyfilm. 500 gauge upwards. Important: Taper the duct -this allows the size of the exit holes down its length to be uniform. When laid out flat , ratios of widths at