We strongly discourage the use of duct board wyes for splitting air flow to different areas. The estimated equivalent length of a duct board wye is approximately 150 feet at 900 Feet per Minute. The key flaw with fittings made into a triangle is that air flows into the expanded space and loses forward momentum or velocity pressure. Then the air must flow out of the triangular space back into a constricted round outlet with no assistance from vanes to direct the air in a smooth predetermined direction. This causes an increase in resistance or static pressure and again interferes with smooth powerful directed flow of air to the intended outlet. We call these duct board fittings “Bermuda Triangles” because they are the place where air goes in and does not come out the other side.
