# Does tea cool down faster at altitude than at sea level; is the rate of cooling faster?

I've found this question impossible to find online because all the answers talk about the boiling points and freezing points at different altitudes.

The question is whether the rate of cooling or heating changes with altitude. So, practically speaking, if the boiling point is 90 C because I am at elevation, it takes x seconds to cool from 90-80 C. Assuming the same ambient temperature and dew point (I suppose), etc., will it cool slower from 90-80 C at sea level, take the same amount of time, or cool at a faster rate?

More broadly, does it generally take water longer, the same, or less time to cool at higher altitude. Or, does water cool faster at altitude? (Not really how or why it changes faster, the same or slower at altitude just whether it changes and approximately by how much.)

I do not mean to ask whether it will it take longer to cool to 80 C from the respective boiling points.

My hypothesis is that the rate of cooling would increase with an increase in altitude. I've found it really hard to get across what I mean without someone launching into the intricacies of humidity and all the rest to the point where I have no idea what the person is saying other than "it depends." So I would appreciate if anyone can answer in plain English whether my hypothesis is correct.

Methods/What I have tried:

I sit with my cup of tea and notice that I have to heat it up after a shorter period than I kind of remember it being at closer to sea level. This is not an experiment, just a general observation, and I am hoping for a general answer. I can't really try anything because I can't easily rush back and forth between the mountains and the 200 km distant sea, nor do I have any apparatus to speak of. Anyway, it's not an experiment, just a general question :)

• This can't be answered with a simple yes or no. The cooling rate of the tea will depend on a lot of factors, both of the vessel in which it's stored and the air around. Commented Mar 29 at 12:52
• Well, I'll take that as another failure to communicate. Ceteris paribus, all other things being equal, under identical conditions except one, etc. etc. Not sure what else I can say. Thanks for taking the time to answer, but honestly put, it wasn't lost on me that the vessel and factors like humidity, which I mentioned, would play a role. Commented Apr 7 at 0:57
• No, that's not the problem. The problem is that you can't just say "all other things being equal", because the concrete choice of equal parameters influences which of the two cools faster. And it's not even clear how you would define "equal". For example, humidity could be absolute or relative, equally-strong wind could mean the wind speed is the same or it could mean dynamic pressure is the same, etc.; in either case the other parameter will then be different. Commented Apr 7 at 16:33
• I know, I know, I know, I know. I will respectfully say that this is why scientists have a reputation for being bad communicators. If you must cling to some "it depends" parameters, define them (simply) and answer the question. I taught 20 years, and I can say that this is how it's done. Saying it depends, then thinking a better explanation is a more detailed explanation, then explaining as if the person is an idiot, and next calling them an idiot is the MO for way to many scientists. It's amazing how many either have to show off or can't release from that. End of rant. Commented Apr 9 at 21:24

TLDR - It usually cools faster, but heats about the same rate.

The rate at which water heats depends on how fast heat is added to the water and how much water is being heated. We will assume you use the same amount of water each time.

If you use the same stove each time, you would expect the same amount of heat to be added to the water. But things are different at altitude. Primarily it is colder out and the air pressure is less. So you need to ask if that affects how fast heat gets from the flame into the water. And that isn't a simple question. Here are some things I would guess might have an effect.

• Less air might affect how the stove burns. It the flame as hot?
• Does air pressure affect the shape of the flame? If it gets wider, some hot gas might flow away from the pot before heating it.

The temperature doesn't affect the rate of heating. But if you start with colder water at altitude, it takes longer to get up to a hot temperature. That is counteracted by the temperature of boiling not being as hot at altitude.

The rate at which water cools depends on how fast heat escapes from the water. There are a number of ways this can happen. So again, it depends.

The primary way for heat to escape is often evaporation. This is definitely affected by altitude. With less air holding it back, it is easier for water molecules to escape from the water. This is also why water boils more easily at altitude. These molecules carry heat with them.

• If you put a lid on the water, you block the molecules from escaping. They and their heat often go back into the water. This slows cooling.
• If you cook inside a tent, the tent acts a little bit like a lid. But it isn't as effective as a lid in preventing escape.

If you put a lid on, heat can still get out. The water heats the pot, and the pot heats the air around it. There is less air to carry away heat, but the air is usually colder.

• Thanks; this part is what I thought was the relevant factor, meaning, yes, it cools at a slower rate. "This is definitely affected by altitude. With less air holding it back, it is easier for water molecules to escape from the water." Commented Apr 7 at 0:53