Reheating of water woun´t happen but the aim of the second rad is defeated.
Front mounted rads perform better than rear or top mounted rads that has to draw warm air from inside the case.
The direction of air flow/which rad gets the water first in stacked rads will play an important role when the configuration is being used. I have tried single rad with front and later back mounts and i noticed that i lost about 4~5°c difference in temp with front mounted rad but other hardwares get heated up from the heat being dumped in the case. Thats why i went with a external mounted rad. The bottom line is that when the water flow from rad1 to rad2 and the air flows thur rad1 to rad2; the water exiting the rad2 will not loss enough heat due to warm air coming from the first rad1
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