When does floating energy (and power) disappear from your pool?

Ruling: Energy and power disappear at the end of each turn and at the end of each draw phase.

Nuances:

• You can recycle runes to float power even when not paying a cost
• The draw phase clearing almost never comes up; its purpose is to prevent exhausting and recycling 2 runes in your Beginning phase with an empty rune deck, channeling those 2 runes, and having access to 14 energy in a single turn
• Floating power can be useful in edge cases, such as when you have 12 runes on board and cannot reveal another rune from your rune deck for cards like Twisted Fate