Does water boil faster in a covered or uncovered pot?

I cook soup daily so I do my fair share of boiling water. I always cover up the pot when I heat the water to make things go quicker.

I mean, it just makes sense: the cover traps the heat that would otherwise escape so that should heat the water faster. Plus, the very existence of pressure cookers would suggest that trapping heat makes for an efficient cooking method.

But a few years ago one of my friends questioned this logic. He is a smart guy from an Ivy League college, so I didn’t just brush his opinion aside.

He agreed with me that covering a pot should trap in heat. But on the other hand, he reminded me of a bit of chemistry. When you cover the pot, you are creating pressure inside the pot which will increase the boiling point of water (known as Gay-Lussac’s law).

So he wondered, might covering the pot actually take longer due to the increased boiling point of water?

The answer is no, it’s still better to cover. But let’s confirm this and understand the reason why.

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"All will be well if you use your mind for your decisions, and mind only your decisions." Since 2007, I have devoted my life to sharing the joy of game theory and mathematics. MindYourDecisions now has over 1,000 free articles with no ads thanks to community support! Help out and get early access to posts with a pledge on Patreon.

My small experiment of boiling water

I thought it would be fun to actually boil some water in pots and see how much of a difference covering makes.

I used the following experimental design:

–I weighed out 16.00 oz of filtered room temperature water
–I used a 4 cup stainless steel pot (the pot can make a big difference)
–I set my gas range to a high flame
–I used a stopwatch to record when boiling occurred
–Every minute I measured the temperature with an IR thermometer gun for the center of the water
–I did not stir the water

I repeated the process using both a covered pot and an uncovered pot. For the covered pot, I would very briefly open the lid to get the temperature reading every minute. I knew it was boiling by the sound, and also I had a rough idea of when it would boil since the temperature of the water increased almost linearly.

So here are the results.

The covered pot boiled quicker at 4 minutes and 15 seconds. The uncovered pot took an extra 30 seconds to boil at 4 minutes and 45 seconds.

I stopped the experiment at 212 F when the water was boiling. Here’s a graph I made of my temperature readings:

(Note: the covered pot also boiled around 212 F, so there wasn’t much increased pressure to raise the boiling point.)

So there you have it: one confirmation that it’s faster to boil water in a covered pot.

Important caveat: You have to be vigilant when boiling with a covered lid so the water does not boil over. For this reason I always cook soup uncovered after I get the water to a boil.

The reason why water boils faster in a covered pot

It is true that covering a pot will increase the pressure and raise water’s boiling point. In many pressure cookers, water will boil at 120 C (248 F) which is quite a bit higher than the normal boiling point (100 C / 212 F).

But this effect is minimal compared to another effect. When you cover a pot, you are trapping the heat inside which is energy that can be used to heat and boil the water faster.

As explained on this educational website:

In the uncovered pot, as the water heats up and gains energy (temperature), some of that energy is used to change the phase of the water from liquid to gas. The energy this phase change requires is called the latent heat of evaporation. As the water heats up, some of it changes to water vapor, using up some of the energy that the water would need to boil.

The water in the covered pot will also lose energy as some molecules change phase (liquid to gas). However, since there is a lid, the gaseous water cannot escape. It will condense on the lid, which releases energy (the latent heat of condensation, which is the same amount as the latent heat of evaporation) back to the liquid water. In this system, very little (if any, depending how tight the lid is) energy is lost, and the water will have more energy and boil faster.

In conclusion: it is definitely a bit faster to boil water in a covered pot. True, it’s on the order of seconds and minutes, but in our busy lives every second can count.

So next time you need to boil water on the stove, save yourself some time and cover up.