# Boiling Water question, lid on or off?

If I’m boiling a pot of water, will it come to a boil faster with the lid on or off? My pal thinks it’s a waste of energy to boil water without a lid, I say that if the lid is on, how do you know it’s boiling? And don’t we really just leave the gas on for the same length of time and at the same setting anyway? Sheesh.

Boil with the lid on; it’s more efficient. The escaping vapors take heat with them. If the lid is on, the vapors condense on the lid, retaining the heat in the pot.

From my experience it seems significantly faster to boil water with the lid on. I don’t have time right now, but it wouldn’t be too difficult to conduct a wee experiment in the kitchen and find out. And how do you know if it’s boiling? Umm, you check? Or sometimes you can tell because the lid is rattling from the pressure of the steam.

You don’t need to keep the lid on all the time, you can lift it to check, and it has a tendency to jiggle when the water boils. The lid helps keep the heat inside the pot, rather than letting it escape, so it should help the water boil faster. Without an experiment, though, I can’t say how much time you would save. Assume it takes 3 minutes less to get to a boil, you can start cooking 3 minutes earlier and turn off the burner 3 minutes earlier, that’s an energy savings. You might also be able to boil the water in the same amount of time, on a slightly lower setting.

It could also be true that the amount of energy saved is miniscule in comparson to the amount used overall, but that would take an experiment to prove/disprove. I don’t think it’s easily estimated by just thinking about it, and there are a lot of factors that effect the situation.

Well, technically, if water vapor is condensing on the lid, it is because it is giving up the heat that changed it from a liquid state to a gas. The heat is absorbed by the lid, and re-radiated into the room.

I’m not so sure about this. Wouldn’t keeping the lib on tend to raise the pressure and retard the onset of boiling?

I agree that the water temperature would probably go up faster with the lid on than with it off but boiling is another matter.

But it only gives up enough heat to turn into a very hot droplet of water, not the cool one it was when the process started. And at least some of that heat is radiated from the lid back down into the pot.

Some of that heat goes back into the pot. The lid also limits mass transfer of steam, and its heat content, out of the pot.

Not necessarily. It would depend on how tight of a seal your lid makes. Most of the lids I use don’t make a very tight seal; also, once it jiggles from the boiled water, any excess pressure can bleed off very quickly. (Now, a pressure cooker is, of course, another story.)
Where do you all think the phrase “A watched pot never boils” comes from?

Put a lid on it!

Even if the lid raises pressure by one PSI (2.036 inches of mercury), it’ll only raise the boiling point by 2.9 degrees. Of course for an 8 inch lid to hold that pressure in by its weight alone, it’d have to weigh 50 lbs.

No doubt the lid doesn’t raise the pressure by much, but it does raise the pressure. Can we agree that the water will heat to 100 C a trifle faster and boil just a tad later with the lid on?

I actually kind of did an experiment involving this question when I was making strawberry jam a few weeks ago. When I was sterilizing my first batch of jars, the lid was not on the canner so I could see when the water started boiling to start timing the process. The second batch I had the lid on the canner, and the water seemed to come to a boil significantly faster. I didn’t time it, because I didn’t think of it until I was doing the second batch.

… and that the combination of speeded up heating and retarded boil might just result in a decrease in the over all time taken to reach boil?

Surely this is a no-brainer. Keep the lid on - the water boils quicker and you don’t steam up the kitchen so much.

Sure, the increased pressure will increase the time to boiling slightly, but blocking mass transfer of steam with a lid will effect a big decrease in the time to boiling.

With the lid on, it heats up significantly faster and boils at a very slightly higher temperature. Net effect: it boils significantly faster.

If you want to warm up and humidify the kitchen, leave the lid off. If you want to boil water, put it on. If you want to know if the water’s is boiling, lift the lid and look.

This is true, but the net effect depends on the comparison of a trifle to a tad. We can estimate the pressure part of this pretty easily since it’s based on simple calculations.

An 8" lid has about 50 square inches of surface area. If it weighs 1 pound, we have a maximum increased pressure of 0.02PSI (1/50). The pressure increase is roughly linear, so 0.02PSI x 3 Degrees F = 0.06 deg increase in boiling point. We’re increasing the temperature by about 140 deg, so the increased pressure adds 0.04% to the heating time (.06/140). If that heating time is 10min, 0.04% is about 1/4 of a second. The increase in temperature is certainly real, but small enough, I think, to consider irrelevant for our purposes.

I don’t think my math is wrong, but I wouldn’t mind a second look.

What kind of lid boils water faster: metal or glass?

<bolding mine>

[Nitpick] - the original saying from Poore Richard’s Almanack would be better paraphrased “A watched pot never boils OVER” meaning that if you keep an eye on your affairs, they’ll not get out of hand. Where the shortened expression meaning that things seem to take longer if you’re waiting on them comes from, I have no idea. [/nitpick]

Meanwhile, back at the OP - put me down in the lid on boils faster camp. The amount of heat loss from evaporation is much greater than the minimal increase in boiling point due to pressure. Even if a fair portion of the heat is radiated away by the lid, some of it is radiated back to the water and more is conducted through the lid to the pan, whereas without the lid, all of it is lost to the atmosphere.

No kidding? Shucks, and here I thought I was onto something.

I still like my explanation, tho…