My question: What is the ideal gap between two panes of glass for insulation?

According to this: Are engineering questions appropriate for this site?

When constructing a product for use in the world, there are many considerations that go into the decision-making process. The underlying physical principles are only a part of this. The physics community, while often tangentially knowledgeable in these areas, is not the place to seek guidance when ease-of-use, manufacturing costs, material availabilities, etc. are also primary considerations.

Ease of use, manufacturing costs, and material availability are not considerations in my question. I specifically said that it doesn't matter how impractical it is. The material is not a variable. I just want to know what the ideal gap is (and how to arrive at that information), which I suspect makes it a physics problem. A physics problem I still have no idea where to begin with.

All of the responsibility of engineering it: thermal expansion of glass vs. the frame, size of the glass, strength of the glass, whether the glass will bow or break under its own weight, whether the gap is too large or small for my limitations, fog between the panes of glass, etc. are all not in question. In order to make my sad rendition of a "good" balance of these factors, I need to know which direction "perfect" is, and I don't.

Please understand the answers I've found range from "basically as close possible without touching" and "wide enough to stick your finger in there".

Yes, I include a specific thickness of the glass, but how does that make it engineering? I suspect that things like how thick the glass is, whether it's glass, the temperature of the air, the fact that it's not argon (which is what manufacturers put between glass layers) are required information to get an answer that doesn't contain the words "not enough information".

I'm asking how to determine a single dimension under idealized circumstances. It's a five-layer sandwich of infinite planes of: hot air, glass, air gap, glass, cold air.

If that isn't physics, why isn't the question that my question links engineering also?

  • 1
    $\begingroup$ Engineering = application of science to the real life. While I believe it is a better match to the Engineering SE, its science part is enough strong the leave it open (reopen). The border between science & engineering is fuzzy. I would ask such a question on the PSE only if I would want to know the science part of the answer (i.e. learn about the related theories). If you want an engineering solution to an engineering problem, Engineering SE is the better match. $\endgroup$
    – peterh
    Commented Jan 31, 2021 at 20:24

1 Answer 1


I can actually see several reasons why this question doesn't fit, including the engineering reason that it is closed for. I'll go through my opinion on them.

For off topic as engineering, I don't think that blurb you quoted gives the whole picture on why something could be seen as an "engineering" as opposed to physics question. The problem is that the question really isn't asking about physical concepts as much as it's asking about results of the practical application of those concepts under certain conditions.

This actually leads me to another reason one might close; the homework and exercise policy. The first part of your question can basically be distilled down to "What is the solution to this word problem?"; this isn't particularly helpful to future readers, as it only addresses a one specific example instead of the broader application of concepts.

You might then point out that there are several questions under that which are asking more about concepts; which leads to the third potential close reason. The question is too broad. Your question should focus on a single question, but your second paragraph seems to ask three different questions along with the first one.

I think it's possible to get some answers to the things you want to know by formatting the questions better, but you would need to avoid off topic reasons. I would actually consider posting some version of it to Engineering SE perhaps (though I'm not sure what part you should focus on, it still seems too broad). That site might be a bit less active, but I suspect people there would be familiar with the situation you're talking about and possibly even be able to point you to good resources on it.

  • $\begingroup$ "Because the question is so specific, it's homework and a word problem and therefore not helpful to future readers, but the part where I do ask about the general physics concepts that would be useful to future readers is too broad. I should refine my question by breaking it into more specific questions despite receiving no information as to which parts are relevant." $\endgroup$
    – gunfulker
    Commented Jan 29, 2021 at 1:51
  • $\begingroup$ @gunfulker I can't tell you which parts are most relevant to what you want to know. You asked several different things. $\endgroup$
    – JMac
    Commented Jan 29, 2021 at 2:03
  • $\begingroup$ I explained the exact situation in so much detail that my question got thrown out as a homework problem, but simultaneously not enough information to tell whether the given parts of information were relevant to the solution of the specific problem. Maybe I should ask the philosophy stack exchange. $\endgroup$
    – gunfulker
    Commented Jan 29, 2021 at 2:20

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