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Tips Before You Buy -- How a Duct Hose is Measured
The size of a piece of ducting will normally have to be very precise. To make sure you get the exact size you need, you should know the basics when it comes to measuring a duct hose. As long as you know how to measure the length and diameters of a duct hose, you should be good to go.
One of the most important aspects to be aware of is how the length of a duct hose is measured. Because a lot of ducting comes in flexible forms and can stretch considerably, this can cause some serious confusion. When it comes to the length, the measurement will refer to the hose at its most extended point – the absolute maximum length it can represent. In other words tow people pulling in each end of the hose should get it to its maximum or selling length. A compression ratio could also be recorded. This tells people what size the hose can be reduced down to. For instance, a ducting product with a 5:1 ratio would be 5 ft at its maximum length, compressing down to 1 ft at its smallest point.
Another key figure in the measurement of ducting is the diameter. This is the size of the circular opening at the end of the duct hose. If a straight line was drawn across that circle at its greatest point and measured, that number would be the diameter. It should not be confused with the circumference, which you would get by measuring around the circular opening. There are two separate diameters often recorded, labelled ID and OD – inner diameter and outer diameter. The ID measures from the inside edge of the ducting wall. The OD will be slightly larger, as it measures from the outer edge, taking into account the thickness of the ducting wall.