It ain't the heat, it's the humidity.

That, and the air isn't circulating properly.

Possibly the oxygen content doesn't get rebalanced by diffusion or circulation if enough of it gets respired and exchanged for carbon dioxide? Known that to happen in certain types of enclosed spaces (submarine hulls, railroad tank cars) in which people are working. It's something you have to plan for ahead of time and provide a solution so folks can do their stuff safely. ("Hey, anybody seen Frank this afternoon?")

I've been in enclosed spaces that weren't noticeably warm but there wasn't really enough oxygen, and the stuffiness was noticeable but not immediately so. Like you, grouse, I'm curious as to why I perceive it more quickly in warmer air.

Interestingly (to me at least) the oxygen content in a room never decreases by much, if at all. We exhale a lot of oxygen along with the co2 and all the other stuff.

Stuffiness is subjective. It can be the increased humidity with all the exhaled breath, the increased co2, which causes some physiological changes (such as slowed breathing) that happen below our awareness.

When I try to explain the whole IAQ (indoor air quality) concept to building occupants, I use the very technical word "cooties" to describe all of the stuff that we exhale, along with skin cells we slough off, odors we emanate (whether natural or from stuff we put on our bods) along with the co2, co, and the rest of the gasses we exhale.

But iconomy is right (I would never mention it, even if she was wrong), when the air is not exchanged with enough outside air, it gets more humid.

I have lots of fun machines that I use for this, and part of the joy for me is just (when I am in the mood) completely bs'ing people about what the numbers and graphs mean. That said, all of the above is the truth.

Confined spaces, such as submarines, tank cars, etc. are a WHOLE other issue.

So I can sense increased CO2 in a way that causes me to think, "wow, it's stuffy in here?"

grouse. . .it's the increased co2 plus all of the other irritants that get built up in the air. . .dust, cosmetic and other detrius from humans, bits of fabric, off gassing from finishes such as paints, formaldehyde from cubicle walls, etc etc.

It's all of that stuff. . hence, I just use "cooties" and people seem to get it.

BTW, the guidelines for CO2 in a room state that it should be kept to 1000 ppm but it's hard to do that. Outside, it's pushing 400, by now.

danf, "cooties" (for me anyway) is that mythical infestation you'd get from touching a member of the opposite sex when we were kids...never thought I'd see the term repurposed like that.

On submarines (again) "cooties" were known universally as "boat funk" -- step aboard a boat that's just back from at least three weeks submerged, and it smells like all the body smells you can think of, ozone, industrial solvents, machine oil, really old locker room, food smells, and (depending on whether they've blown the CHTs lately) a faint whiff of sewer. But weirdly, it's never stuffy on one (I'm talking nuke boats here -- maybe some Euro sailor can talk about D/E boats) and the air conditioning means that it's never "stuffy" (except when they secure the blowers as part of rigging for "ultraquiet") and it's not even slightly warm, either (except for the engineering spaces during speed runs).

Today it's about 17 C and threatening to rain or raining, and a couple of people have said their parts of the office are "stuffy" despite audible blowers running. Neither the A/C or the heat seem to be working.

(Nor do I, I suppose...)

Whoa, submarine thing! Huh. I always thought cooties derived from the slang term for...well, crabs.