As the missus likes a deep bath at the temperature of lava it always seems an incredible waste of heat but to use it.
After she gets out I leave the bathroom door open for 10 minutes to let heat into the rest of the house then slowly let myself into the still scalding water where I wallow for an hour checking emails, nsc, maybe listen to a podcast.
At this stage the water may have cooled enough to become merely warm so feeling that full value has been extracted and that I am sufficiently pre soaked I have a quick wash and exit.