I believe since the advent of the overfill prevention device, 20lb tanks are filled to a max of 17.5lbs. When fuel prices sky rocketed a lot of the swap propane companies went to 15lbs basically keep their price lower and roll the wool over the consumers eyes. I basically read this on a sign on an AmeriGas propane tank cage about a class action lawsuit against them…
It is pretty much always a better deal to get a tank filled then to swap. First you are paying for what they actually give you… If they only fill the tank half way, you only pay half the price. Second the price by volume is usually cheaper. The only thing that is a PITA with filling is the hydro date on the tank, which is something you don’t have to worry about when swapping them. That being said a lot of the swapped tanks are either near out of hydro or they don’t stamp the tank so you can get it filled…. you are then stuck swapping it. Don’t be afraid to look at the date on the tank when swapping and if it is near out of hydro, ask for another one. I believe hydro tests are good for 10 years.