even our ability to align and read the thing!.

but you can find the velocity in an equivalent (P drop wise) round duct.Īs for the velocity in the 'round duct equivalent' to the 64 x 60 rectangular duct, the ductulator is quite accurate given its limitations and weaknesses (mine is cardboard): cardboard shrinks and swells with moisture changes, the accuracy of the printing, the exact centeredness of the pivot point, the thickness of the logarithmic scale lines. This doesn't mean that you can use the ductulaor to find the velocity in rectangular ducts. Notice that on the instructions of the ductulator it says that the velocity is 'The DESIRED velocity in a ROUND duct'. There are laborious tables to do this calculation of equivalency but the ductulator is much simpler.

On the ductulator, it means that all things being equal (shiny sheetmetal to shiny sheetmetal), 100 feet of straight, round, metal duct has the same pressure drop as the 'equivalent' size of 100 feet of straight, rectangular duct as shown on the ductulator. The term 'equivalent' round duct (to a rectangular) or 'equivalent' rectangular (to a round, does NOT mean that they have the same area (and therefore the same 'average' velocity). In looking thru this section, I was reminded of some basics (one of which is that I am NOT a fluid dynamicist!): The pressure drop thru round and circular ducts of the same cross-sectional area is NOT the same. to make sure we're BOTH using this WONDERFUL, time-saving tool properly and to be sure of my 'faith' in it!) So I broke out my 1989 copy of the Trane 'Blue Book' which explains the ductulator's use and duct sizing in general starting on page 283 thru of chapter IX. Having worked at Trane for 25 years (I am now in private HVAC practice), and since that 'Tatoo' still hasn't quite come off in the shower, I felt compelled to respond! I TOO use the ductulator almost EVERY DAY!!! (maybe that's the real reason I wanted to reply?.

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