Sleep equations:
Cold night + hot tub= good nights sleep.
Cold night + hot tub + 1-2 beers (or whatever) = GREAT night's sleep
Cold night + too many beers = waking up in the middle of the night = CRAPPY night's sleep
Warm night+ 30 minutes to cool off = great night's sleep
Warm night+ going to bed immediately= weird dreams and poor night's sleep
Stressful day at work= poor night sleep
Stressful day at work + hot tub= who cares about work
I could go on, but you get the idea.