The sampling tube is identified by a series of air inlet holes on the tube. The
sampling tube is always installed with the air inlet hole facing into the air
flow. For duct widths greater than 18 inch, sampling tubes must be purchased
separately. The recommended length is specified below. It is also recommended
that the sampling tube length extend at least 2/ 3 across the duct width for
optimal performance. Sampling tubes over 3ft long must be supported at the end
opposite the duct smoke detector.