Working on the ducts for my shop. Just installed a CV1800 with the 16" impeller. Question is, for the vertical drops, am I better doing 45 degree turns down, with a section of 6" metal pipe, then using a perhaps 24" long or so, section of flex tubing? Or just do a 90 degree turn with a straight pipe connected by a very short piece of flex pipe? Basically does the longer length flex pipe outweigh the better 45 degree turn?

Any other suggestions or 'rules' would be much appreciated.