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As a sidenote to this question: Why do European 19th century kitchen stoves for solid fuels often have circular openings on top? Is the heating more effective if there is no additional metal between the fire and the cooking vessel on the stove? Cast iron is a good conductor for heat, so I would assume it does not make so much of a difference?

I have tried googling, but all I found was that the rings allow you to enlarge the opening on the stove, not why you would want to enlarge said opening.

An old kitchen stove (image source)

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    Aren't most pots and pans round?
    – MCW
    Jan 29 at 23:01
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    Depends on era - many of the old pots I have seen don't have a flat bottom, but a rounded one. That would give pretty bad heat conduction if placed on a flat surface, but would work fine in a round hole. But I don't know what kind of pots were common in 19th century Europe.
    – jpa
    Jan 30 at 7:21
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    @jpa non-flat-bottom cooking wessels were indeed common in 19th century (as well as way earlier and somewhat later)
    – fraxinus
    Jan 30 at 13:08
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    @Jan: there was a door at the bottom for that, but too small to load wood into. Jan 30 at 22:58
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    Cast iron is actually pretty bad at conducting heat, compared to other metals used for pans. Aluminum is ~4x better and copper is ~ 8x better. Iron may not be a insulator, but I wouldn’t call it a “good conductor for heat” Jan 31 at 1:40

6 Answers 6

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I have no reference other than personal use and observation, having once lived many years in rural areas where virtually everyone used wood stoves.

Yes, you may remove the appropriate sized plate and put your cooking vessel directly open to the fire beneath. This is one way to adjust the heat to the cooking vessel, as is simply moving it to a part of the stove further from the firebox.

People often also add (small amounts of) wood to the firebox through the top rather than the opening in front.

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    In particular, there were special pots of different sizes that could be inserted into the range with the appropriate ring(s) removed. An example is shown in this YouTube video (in German, but the demonstration works in purely visual fashion). Yes, this was done for efficiency reasons.
    – njuffa
    Jan 30 at 5:20
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    Also, you don't have to completely remove the plate, you can just pull it open a little and you might do this with no pot on, to increase the air draw through the stove for a little while. Jan 30 at 17:30
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    Though not for «heating with fire», the principle still is used in some chemistry labs when you partly immerse beakers, Erlenmeyer flasks, etc. in a water bath (example, and (less frequently) heating with steam of water (example). Oh and if your are worried about these flasks would tip while afloat, they just get a ballast ring around their neck.
    – Buttonwood
    Jan 30 at 21:03
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    It's funny to see people describing these ranges as historic: my parents still use one.
    – TRiG
    Jan 31 at 23:30
  • Once the pot is boiling, you can re-insert the CI disc to simmer. (I have a kerosene stove like this on my boat) Feb 1 at 17:12
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You take out the rings so that the bottom of the pot is heated by the air from the fire.

If you put the pot directly on the metal, you can only transfer heat by conduction, but to get efficient heat conduction the contact area has to be large. However, in the time that these stoves were used, pots, although they generally had a flat bottom, were not precisely engineered but even often hand-made. Also pots were used for a long time and tended to have a lot of scratches and bumps after a while. And the stove itself is cast-iron which is also not perfectly flat.

So the pots would not sit very evenly on a metal surface and the contact area would be small, making heat conduction quite inefficient. Such pots with uneven bottoms are better heated directly by the hot air through convection and radiation from the flame. Modern pots designed for electric stoves have a very smooth bottom. But note also that now induction heaters (which generate a current within the pot and heat it directly) or infrared stoves are becoming more popular, as they don't depend on heat conduction between two (possibly uneven) surfaces which is notoriously difficult to do efficiently.

This is based on own experience with these stoves. When you finished cooking and wanted to keep the food warm but not heat it any further, you'd move the pot onto the metal. Even though the metal was also burning hot, it didn't burn the food.

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Related to this, vintage cast iron pans have a heat ring that corresponds to different stove hole sizes.

With the advent of wood-burning stoves, pans were produced to conform to the sizes of the openings in their tops known as "stove eyes". Think of a stove eye as a burner on a modern stove. (Some people still call them that.) A heavy cover piece was left in place when an eye was not directly in use, and removed-- using a special, heat-resistant lifter handle-- when maximum heat from the eye was required.

Heat rings, the rims protruding from the bottom circumference of most early cast iron pans, served multiple functions: as a "seal" of sorts between the pan and stove eye, as added stablility for less-than-perfectly flat pan bottoms, and as a device to help reduce hot spots.

Depending on the brand of stove, and the sizes of its various eyes, appropriately-sized pans would need to be purchased for use with it. Or, in some cases, the stove maker also produced pans, which they supplied for use with their units.

http://www.castironcollector.com/numbers.php

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Your assumptions are wrong. It's easier to see why if you change the context slightly.

Imagine a pot of water boiling on a gas stove. Now imagine you have the opportunity to insert a cast iron disc between the fire and the pot. Would you do so?

Generally, you would expect the disc to be less efficient at boiling the water, becasue it would "block" the heat from getting to the pot: some would get absorbed to warm up the disc, some would get radiated off in other directions, etc. You also have the surface effects, where a hot fluid (the air in the stove) is going to have more heat-transferring surface area than the pot-disc interface.

So yes, removing the cover makes it more hot.

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    While this might deal with some false assumptions in the question, it doesn't really provide an answer to the question itself.
    – Steve Bird
    Jan 30 at 14:46
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This looks more like a physics question than an historical one. I saw several stoves like that, although I never used one and I'm confident they were made that way because there was a perceivable advantage.

From a physics point of view, I'd say the main advantage is using convection rather than conduction to transfer heat to the pan. The hot air would reach the bottom of the pan, cede heat and then fall down, replaced by more hot air coming from the fire.

  • You obviously do not want a hole larger than the pot, so that the hot air (and the smoke) is not lost to the room,
  • you also do not want the hole to be too small, so that the transfer from the hot air is quicker and more uniform. You don't want the food to get burned in the middle and still be uncooked at the edges, nor you want to heat the metal rings unnecessarily, costing you time and fuel.
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    In an adequately vented wood stove you don't lose hot air to the room. In an opening like this, air is sucked in.
    – fraxinus
    Jan 30 at 13:04
  • @fraxinus that's really interesting. Wouldn't the cold air coming in be harmful to the cooking?
    – Rad80
    Jan 30 at 13:34
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    The cold air coming in can as well increase the heat power of the stove (by bringing more oxygen). Or lower the heat power (by reducing the chimney draft). It depends on the stove geometry and the fuel placement. Both effects could be intended. Either way, you really don't want "hot air" getting out, because it will actually be smoke and not air. This happens when the chimney is clogged or when cold-starting the stove in a hurry.
    – fraxinus
    Jan 30 at 18:55
  • "You obviously do not want a hole larger than the pot" - because the pot would sit in the middle of the fire preventing air flow, generating smoke and make you die because of CO and CO2? Jan 31 at 19:24
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I watched my grandmother time and time again pull the hob eye out to put in more wood specifically for that part of the stove or to stir it down to cool that area or hob of the stove. I never saw her take the hob eye out and set a pot directly over flame, she cared for her cooking utensils more than just not having the time to heat it up faster. The term hob is not used much anymore and has changed in meaning over the decades. If I remember correctly, my grandmother called them plates. I've heard them called everything so it doesn't matter. My grandfather would get up and build a fire in the kitchen wood stove then bring in different sized kindling filling up my grandmother's wood box. Then he would milk his cows. When he was done milking the cows and and coming back, my grandmother would have every thing set up and was cooking breakfast. When he walked in the door setting down the different 5 gallon cans of fresh milk my grandmother would tell him whether she wanted warm milk for breakfast or cold. If she wanted warm he poured out warm into a pitcher for her, put the lid back on and put it outside to cool down. Then he would wash up and go sit down at the table in time for my grandmother to put food on the table for everyone. Her kitchen would stove was bipowered she could either use the wood to heat it or she could use electricity. I do not remember her ever using the electric part other than the clock that was in the kitchen stove.

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