If you are in fact pressure canning something it only requires two or three quarts of water per the instructions. If you're water bath canning then you have to fill it two to 3 in above the level of the jars and that can require a whole lot of BTUs. But you can't shorten that time with a propane burner. Your canner came with a yellow piece of paper that told you under no circumstances should you expose it to a temperature above 12000 BTUs because it will distort the metal and ruin the pressure canner resulting in a catastrophic failure. Which is about the temperature of the large burner on your stove. A propane burner does a whole lot more BTU and there's no safe way to know when you've hit that limit I recommend starting boiling water early If you're going to do water bath canning.