Huge DCs like Amazons and ours at Google are very efficient, cooling uses at most 10% of total power. So cranking up this wouldn't help. Nor wouldn't it be possible usual anyway, as these are typically using evaporation cooling, which can't really be cranked up like traditional compression cooling. And keeping a huge tank and heater ready would introduce another point of failure. The easiest is just to have your servers do some heavy calculations.
Compared to heating a water tank, it would be a much more responsible use of power to fire up some folding@home images.
Perhaps a more financially responsible solution would be to spin up a bunch of instances that mine some sort of cryptocurrency. I doubt it'd cover electricity costs, but it could offset it some.
