One critical factor for the uniform distribution of air from the tube is to size the tube according to its air handling capacity, not just its measurement in inches. Nordlund says a common mistake is to choose an equal match between the tube size and the fan — for example, a 14-inch tube and a 14-inch fan. “Technically, we size the tube so that air speed inside is held to under 1,200 feet per minute, but a reasonable thumb rule is that the diameter of the tube should be about 1.25 times the fan,” says Nordlund.
The University of Wisconsin offers training on designing positive pressure, tube ventilation systems through The Dairyland Initiative, http://thedairylandinitiative. vetmed.wisc.edu/. Nordlund strongly recommends working with a builder or other professional who has completed this training.
More information from Nordlund on the ventilation systems can be found at http://www.ansci.cornell. edu/prodairy/calfsystems/proceedings/2.Nordlund. Manuscript.pdf.