Some vent caps come with an attached duct ... But when that isn't possible, metallic flexible duct also works. Although it isn't always possible in attic crawl spaces, you should always insulate ...

The ANSI-recognized national standard for residential HVAC duct design will help you design a duct ... sag and compression in flexible ducts; and new equivalent length values for flex duct junction ...

The ANSI-recognized national standard for residential HVAC duct design will help you design a duct ... sag and compression in flexible ducts; and new equivalent length values for flex duct junction ...