Why does my sparge water need to be a specific temperature?
It is generally accepted that up to a point, the hotter your sparge water the better or more efficient.
This is generally agreed to be around 75°C (167°F). Above this temperature and tannins from the grain husks become soluble enough to be rinsed into the grain.
There has recently been some research to suggest that cold sparging has no negative effect on efficiency (though it may result in poorer wort clarity).