Among the more obvious reasons for the use of round duct on rooftops, such as preventing rain, snow and ice buildup, ease of wind passage is perhaps the most overlooked. PhenoliDuct, a new closed-cell insulated round duct solution from Spiral Pipe of Texas (SPOT), is engineered with all those considerations in mind, plus ease of installation.   

In sum, if you have installed double wall spiral duct, you already know how to install PhenoliDuct. The rigidity of the phenolic board and the close tolerances of the duct’s annular construction eliminate the need for an inner coupling. Most installations will only need external bolted companion angle rings or flanges, according to SPOT.

The Kingspan KoolDuct used as insulation has flame spread and smoke developed indices of 10 when tested per ASTM E84, which means you can perform modifications to the duct without worrying about a fire hazard. And nearly all of the SPOT catalogue can be outfitted in a PhenoliDuct construction.

The inner and outer metal shells can be provided as galvanized steel (standard), paint-grip galvanized steel, epoxy powder coated steel, PVC-coated steel, black iron, aluminized type 1 steel, 3003-H13 aluminum, 304 stainless steel or 316 stainless steel. Metal shells can be spiral duct or longitudinal seam welded duct, in a thickness from 10 gauge through 26 gauge.

For more information, contact 817-877-3543 or visit This story originally appeared in the June 2019 issue of SNIPS magazine.