As long as you fill the jars to the bottom of the threads on the side of the jar, you should not have problems with the jars floating. But things happen from time to time and you may have a jar float. To solve this, place something that is both heat save and not buoyant on the jar to beep it submerged. I have a metal meat tenderizer that I use. Another alternative is to place a cooling rack or a colander in the bath with something heavy in/on it to keep the jars submerged in the water.