"Joseph O'Brien" wrote in message
Dryer + elbow + vertical duct + elbow + horizontal duct + elbow +
vertical duct + elbow outside.

By my initial calculations, since I have 3 90-degree elbows (not
counting the one leading outside), I reduce my maximum duct length by
15 feet. Does that sound right? I counted the elbow coming out of the
dryer... is that right?

Yes and if you have a long run, you are asking for problem down the road.
Mine is in a downstairs bath/laundry room and with only two elbows need
cleaning too frequently. Move the washer if you can.