Vinegar to clean water system..How and how much?

What scale? Flushing the water heater tank with fresh water at the beginning and end of each season has always been sufficient for keeping the tank free of any residue. Sorry, I've never heard of using vinegar for scale removal, only for offsetting any bleach smell. I tried it once but felt the vinegar smell was worse than any bleach smell so in the spring after draining off the RV antifreeze I just flush the system with fresh water and I'm good to go. :)