I'm trying to understand how these duct designs I'm getting are so different in duct sizes when done by different companies. I do new home construction and get my designs from four different places.three come from companies from Toronto and one is local. the duct sizes from Toronto are a lot smaller then the local company.i know they design to what they sell. local company is keeprite and one Toronto company is goodman and the other 2 are carrier. but if it calls for a 2ton ac the airflow is 800cfm so lets say the fan for the goodman on medhigh has 835cfm they design the duct for that shouldn't the duct be the same size no matter who designs it. I think that the local company uses bigger ductwork so you paymore if you buy the duct from them.return air is an example Toronto company 10x24 drop and main trunk 8x16.4 joises panned backed to 8x16 duct. local company was 10x26 drop main trunk was 10x26 reduced to 8x18 4 panned back
Some of these duct designs are jokes. I recently did an addition (300sqft)The homeowner had someone do the design. The design for the hot air called for a length of 8x8 for 20ft with 7" top take offs!! How do you fit a 7" tto onto a 8" piece of duct?. I called the guy that drew up the design and told him I didn't agree with the it......he told me to just build it however I wanted and if the building dept had any issues he would draft the design to match my work.......honestly this defeats the whole purpose of the duct design. I ended up running 8x16 for a piece and then cutting down to 8x10 for the last 8ft, all 5'tto. At times I question the software used and individuals who do the designs, seems like some have never swung a hammer. As for the return drop, more surface area is always btr.