Here is what a ducky layer looks like oneof the handier matters that a duck you later can do is it could calculate therectangular duct dimensions to round up dimensions so the very first thing you wantto do is you need to measure your square duct and here we have now 19 inches on theoutside by way of 19 inches over right here as good so what we’ve got is a 1919 rectangular duct sothat’s queer duck however is an inch and a 1/2 thick so what we’re really goingto do is we’ll subtract three inches from 19 and we’re gonna get 16 sowhat we quite have for the within diameter of that 19 with the aid of 19 duct is 16 by16 on the within so now let’s find out what the an identical is that if we’ve a 16by sixteen inch duct to do this we turn this dial right right here to say let’s examine let’sline up see proper here that’s 15 another sixteen so let’s to find the sixteen inch markand let’s see well correct about there I consider wait a minute yeah I suppose so it’sright there say see that is a sixteen with the aid of sixteen so I see with a view to line as much as theequivalent of the round duct to about over 17 so quite you bought to move to 18inches in order that signifies that the equal quantity of duct house within diameter isgoing to be about 18 inches now let’s sayfor instance let’s say our inside of diameter duck used to be will say 20 okayI will say 25 so we line up 20 with the 25 and in an effort to supply us the round duckdiameter similar of about 24 inches now the opposite helpful object that the duckyou laters just right for is calculating the dimensions of duck that your system reallyneeds now offer you an example let’s say you are designing a return duct to be tohave the friction loss will say proper right here k of point zero 5 just for anexample and you have got a three-ton air con method ok rule of thumbevery brand is specific but rule of thumb is that there’s four hundred CFM per tonof air so let’s say your CFM’s are 1200 k in view that well three tons that’sthree occasions 400 is 1200 at zero.25 so they have already style of adjusted the duckyou later to that okay see how you can alter it so whilst you put it again pointzero 5 to 1200 so what you get is just a little over 17 inches of roundduck diameter so that you particularly got to head up one just a little bit more to 18 so you’d bepretty dependable to run 18 inch flex for your return duct on this casenow let’s say for instance you might have a two-ton air conditioning method youwould modify your air range CFM say – 800because you see 400 instances 2 is 800 800 recall let’s examine let’s alter the zero.25to 800 okay right about there that’s about right for friction loss andwe’re getting nearly 15 inches so quite you quite have to go up to sixteen inchesbecause they particularly don’t make 15 inch circular flex so go up to sixteen inches andyou’d be risk-free now every air con manufacturer is just a little bit differenton the design friction loss and the quantity of CFM’s there are per ton so youhave to discover from their specs and use this duct you laterbut almost always talking you can be beautiful risk-free on the return side anyway to gowith point zero five the deliver is just a little bit one of a kind when calculatingthe deliver duct nonetheless invariably go with brand specifications rule ofthumb is you can go along with a factor one for the friction loss and still four hundred CFM perton so at point one let’s see well line this up to say a two and a half ton airconditioning system that would be a thousand CFM’s at factor 1 and that wouldline up the incorrect duct diameter to be about 14 inches and that may be whatyou would want off from the plenum