Flexible duct sizing sometimes can be complicated for non-professionals. Below we have compartmentalized the ideas in a question and answer scheme. We hope that this article answers you questions about flex duct sizing!
What is diameter?
Diameter is defined as the distance of a straight line passing from one end of a circle or sphere to the other end. In other words, it goes straight across the circle. The diameter is a very important unit of measurement when it comes to flexible duct sizing because all duct sizes are measured according to their diameters. Flexible ducting is normally sized according to the internal (or inside) diameter, often labeled as ID.
Do not mistake circumference for diameter!
It is quite easy to confuse circumference for diameter because they are both units of measurement relating to circles. It is very important to know the difference between the two, as they are completely different. Circumference is the distance around the circle. Circumference is not normally asked for in relation to flex duct sizing as diameter is more widely used for measuring flexible ducting.
What is OD?
OD stands for outside (or outer) diameter. It is the measurement of the diameter of the circle from one outside section to the other outside section of a circle. In relation to flexible duct sizing, the total OD measurement will account for the hose’s wall thickness. As a result, OD measurements tend to be slightly greater than the ID. OD size has no real relevance in most flexible ducting sizing, since these hoses do not have a real thick wall thickness and do not require hoses assemblies. OD is important when measuring the outside of the pipe on which your duct will be installed upon. As the flex duct is pulled over the pipe for installation.