I have two panes of glass, about a 3/8" thick (.95 cm). Space efficiency and aesthetics ignored, how far apart should they be spaced to maximize heat insulation, assuming the gap contains regular air (and not argon)?
I read that it's a balancing act between convection and conduction, and that store-bought double panes windows are usually in the 1/4" - 1/2" range (0.635 cm - 1.27 cm). Other sources suggest a gap up to 2" (5 cm) is ideal, with the reasoning that a larger gap is always better up until it's wide enough to allow convection. Assuming it's exactly freezing outside and room temperature inside, approximately what gap size is most insulating?
Additionally, I'm curious why there isn't a consistent answer. For example, does a higher temperature range mean a smaller gap is better, because more energetic air convects easier? Does the glass thickness or number of panes matter? Or does the gap size not matter much, as long as there is one?
Related, an unanswered question that suggests a 6-cm gap: Air insulation cavity depth: rule of thumb to avoid convection
