The reason is because our preferred temperature range is much nearer the freezing point of water than its boiling point. You can only raise or lower the temperature of something if you have something else that is hotter or cooler than the temperature you want to get to (second law of thermodynamics). Room temperature is 15-25°C (59-77°F), our fridges are 0-5°C (32-41°F) and domestic freezers can be as low as -20°C (-4°F).
A stove ring or kettle element can reach over 200°C (about 400°F), so we have no trouble getting water up to 100°C (212°F) given there is a temperature gradient of well over 100°C. But to cool water without freezing it, we only have the fridge, a temperature gradient of about 20°C. Also, an electric stove ring uses 1-2 kilowatts, whereas a fridge uses just 5 per cent of that, so heat removal via a fridge is slower than heat addition via a stove ring.
You could put your glass of water in a large freezer, but the temperature gradient is still just 40°C, much less than that provided by a stove. You also risk freezing the water, possibly cracking the container. Much of the impression that cooling is slower is because we heat water actively, but often let it cool passively If terrestrial temperatures were 80°C (176°F), you could cool water (in a high-power fridge) quicker than you could heat it (before it boiled away).
Mike FollowsSutton Coldfield, West Midlands, UK It has certainly felt that way during the recurring heatwaves many people in the northern hemisphere have experienced this summer. When we heat things, we usually do so actively. A kettle can dump a couple of kilowatts of power straight into a litre of water.
Cooling is often more passive: put a warm object somewhere colder and thermal energy leaks into the surroundings and, as the temperature difference diminishes, that heat flow slows. A fridge speeds up cooling by using energy to pump heat from the cold interior into the warmer room. However, there is no fundamental rule that says water must cool more slowly than it heats.
So, during our everyday uses of water, much of the impression that cooling is slower is simply because we heat it actively and quickly, but often leave it to cool passively and slowly. The more interesting asymmetry appears when we try to cool something below ambient temperature. Then we encounter a less familiar problem: entropy.
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