Is there an apparatus that operates like a double boiler, but loses no steam?

In other words, in a normal double boiler the steam is allowed to escape, so energy is lost and the boiling pot must be periodically renewed with fresh water.

If, however, we make the boiler sealed, then pressure will build up to potentially dangerous levels.

Is there a way to keep the steam captive and reflux it safely back to the boiler without loss of heat except to the vessel being heated?

Note that using a condenser does not solve the problem because energy will be lost to the condenser and even more energy will be required because a pump will be needed for the condenser.

Offhand, the only way I can think to do this would be to have a sealed boiler with a pressure sensor and then reduce the heat when the pressure reached a certain level. That way there would only be a fixed amount of steam so the pressure vessel would (hopefully) never reach dangerous levels of pressure and the heating would be controlled. So, it would be something like this:

enter image description here

I have done searches on "pressurized double boilers" and the only thing that comes up are Espresso machines!

  • $\begingroup$ Why are you worried about loss of water? The point of a normal bath is to control temperature of the stuff being heated (so it doesn't exceed the temperature of boiling water) and water is cheap. Pressurised steam doesn't solve the heating problem as the temperature will rise with pressure. And alternative (non-evaporating) solvents will be more useful (and temperature control can use a cheap thermostat). $\endgroup$
    – matt_black
    Jul 22, 2021 at 13:55
  • $\begingroup$ @matt_black It's not a bath. It's a steam dryer. Losing steam is bad because energy is lost AND not only that but requires that the water be refilled. This process needs to be running autonomously. $\endgroup$
    – Shaka Boom
    Jul 22, 2021 at 15:19
  • $\begingroup$ If you need to control pressure, steam is going to escape. If you need a vessel that can cope with any pressure, the expense will be huge and you won't control the temperature. If you want continuous operation, you could feed steam into the vessel and let it condense in another vessel, but that would require condensation many industrial processes do this, efficiently). I suspect you have incompatible requirements. $\endgroup$
    – matt_black
    Jul 22, 2021 at 22:09
  • $\begingroup$ if the contact between steam and the material isnt necessary, if you're going to use temperature control anyway you should use oil instead of water to maintain temperature of 100°C without significant evaporation = without heat loss $\endgroup$
    – Francis L.
    Aug 21, 2021 at 4:03
  • $\begingroup$ How about an autoclave? $\endgroup$
    – Karsten
    Apr 19, 2022 at 14:54

2 Answers 2


Just use a water or oil bath with an accurate temperature control and stirrer such as these ThermoFisher units or from Thomas Scientific. After all, temperature control is the purpose of a double boiler.

Since your question also concerns efficiency, this is a better solution, since the container can be insulated. If energy were at a premium, e.g., at a remote location, then it could even be sealed, though a safety valve would be needed; in normal operation, it would not vent.

  • $\begingroup$ Steam is required because the vessel being heated must be above 212F $\endgroup$
    – Shaka Boom
    Jul 22, 2021 at 1:11
  • 3
    $\begingroup$ @ShakaBoom, Incorrect: read the answer - oil bath. $\endgroup$ Jul 22, 2021 at 4:46

It seems to me that you want to prevent water vapor from escaping the container. There are different ways to stop this, but having an escape duct for the steam is useful in order to prevent an accident. For example, let's consider that your heating apparatus has an issue, and instead of periodically heating the container which heats the water, it keeps on applying energy. Air pressure in your container might accumulate to dangerous levels until one of two things occurs:

  1. The container melts/cracks due to high temperature, and the vapor escapes.
  2. The air pressure ruptures your container (could be violent).

Both scenarios are not ideal. So an air pressure escape duct is useful. In other words, don't make a container that is prone to accidents.

Now, you suggest that a pressure sensor would be a good way to prevent pressure from accumulating. Your apparatus would measure the pressure, and stop applying heat when the level is too high. My suggestion would be to use a heat sensor instead. There is no need to invest in a pressure sensor that will probably be more expensive. Remember that the ideal gas law (assuming you are not doing precise calculations) relates pressure to temperature; so the temperature probe will do just fine.

Now, there is a fundamental issue with what you are trying to propose. You want to achieve something impossible: "without loss of heat". If you stop applying heat, the already present heat will disperse into the environment. It doesn't matter what kind of container you have, heat will simply be conducted and lost to the environment. As DrMoishe Pippik suggests in his answer, insulting your container will reduce heat conduction, but it does not stop it. You will find yourself spending large amounts of money on an apparatus that simply won't work. Additionally, "keep the steam captive and reflux it safely back to the boiler" is not a smart nor cost-effective idea. Firstly, your gas will cool down, and trying to re-heat the water with the "captive" vapor is just overcomplicating things. However, saunas do exactly that, but they don't re-use their water, and they always heat the vapor again.

Finally, if you don't want the vapor to escape, just use a large container that can maintain all the water in its vapor state without safety issues. Then, your probe measures the temperature and stops heating when it is too high. Since $\ce{H2O(l)<->H2O(g)}$ is reversible, you won't lose your water. And make sure to have an escape duct!

  • $\begingroup$ Losing heat is fine, but we want the heat to be transfered from the steam to the material being heated. We don't want the heat to escape in the form of lost steam. Obviously there would be a pressure release valve in the vessel. The question is: does this kind of equipment already exist? If so, what is it called? $\endgroup$
    – Shaka Boom
    Jul 22, 2021 at 1:13
  • $\begingroup$ @ShakaBoom So you want to be able to take out the material without losing the vapor? $\endgroup$ Jul 22, 2021 at 1:24
  • $\begingroup$ I have added a diagram showing an idea of how it could be done, but note that there is not much design for reflux at all, its just a controlled pressurized double boiler. As far as I can tell, this type of device does not exist as standard lab equipment, but maybe I am wrong. $\endgroup$
    – Shaka Boom
    Jul 22, 2021 at 1:34
  • 1
    $\begingroup$ @ShakaBoom This sort of equipment does exist and is common in industry-scale work in chemical plants or pilot plants. They use site wide steam to heat vessels (on 100kg+ scales). But the plants recycle the steam so steam jackets the vessel under constant pressure and condensed water is recovered and reheated in a closed loop. but this makes almost no sense on smaller scales where simpler heating methods are easier and more convenient. What scale are you working on? $\endgroup$
    – matt_black
    Jul 23, 2021 at 14:21

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