Does water cool down and warm up at the same speed?

A question submitted to us from ‘Phil and the Osophers‘ via Twitter asked;

We thought we’d set about trying to answer the question in our garage lab, however under not so perfect conditions, we only got back some not so perfect results. Without the ability to accurately heat and cool the water equally by the same amount, we experienced the hot water cooling faster than the cold water was warming (the cold water was about 10C cooler than room temperature at the start of the experiment, but the warm water was 30C hotter).

However, under ideal conditions water should, and does, return to the original room temperature at the same speed.

This is because heat transfer is symmetrical; if the water is warming up on it’s own, it is gaining heat from the environment, if it is cooling off, it is giving up heat to the environment.


If our experiment was completely symmetrical, with both glasses of water being exactly 10C above and below room temperature as was originally asked, and if the room temperature didn’t change during the course of the experiment, both thermometers would return at an equal speed.