To ensure proper air quality, base the diameter of the tube on
the fan’s air-throwing capacity, not its size, says Brotzman,
who works with fellow veterinarian Ken Nordlund and UW-Madison
agricultural engineering colleagues to provide farms with design
specifications for supplemental positive-pressure ventilation
systems. One farm they worked with did not follow the design
specs they were given. They ended up with the tube being the
same diameter as the fan. “So if the fan was a 12-inch fan, they
put a 12-inch tube in (which wasn’t) designed to meet the air
produced by that fan,” Brotzman recalls. “Although another
12-inch fan may have worked, that one was producing more air
than what should have gone through that type of tube.” Bottom
line: When you’re going over the blueprints with the builder or
ordering fans yourself, focus on the cubic feet per minute of
airflow provided by the fan, not its diameter in inches. “We
certainly recommend that they go to someone who’s been through
one of our training programs