A/C gurus...how long does it take to completely cycle/replace the air in a room?

[Melbourne]

In a non-perfect mixing situation, some of the stagnant air gets left in the corners of the room for a very long time.

Perhaps fortunately, in a non-perfect mixing situation, some of the corners of the room never really got much smoke in the first place. That’s why you don’t put smoke detectors in stagnant corners.

Also, interesting about the car! We’ve had several threads here about air quality in cars, and there have been a variety of opinions expressed, without much evidence to back them up.

[Napier]

@Snnipe_70E

Not modern cars. My Chief engineer and I were in his mini van traveling from one location to another. We had just purchased a meter that measures CO2 and CO levels in a building, checking for sick building syndrome. We were on the freeway in slow traffic. New meter you have to play with it. We were thinking how bad is the air in this traffic. The readings came close to the normal range, the green area. WE were kind of surprised. WE closed the windows and turned the AC to Max AC. The meter began to rise and in a few minutes it was in the yellow range for CO2. We turned off the Max AC and the meter began to return to the normal range. New cars are sealed tighter today.

So the air conditioning actually seals the car? There are openings someplace and the Max knob position makes them close?

[Joey_P]

@Napier

So the air conditioning actually seals the car? There are openings someplace and the Max knob position makes them close?

Yes, well, kinda.
Max AC (or recirculate) just recirculates the inside air. That’ll make it colder faster and more dehumidified. Turning that off brings in fresh air. I don’t know where it gets it from or how much, but that’s what it does.
Of course, for fresh air to come in, air also has to leave. Most cars have vents, near the back, usually behind the bumper/trim. On this car, it’s that black thing with the 3 louvers, behind the tire.
Turning the AC to max, likely meant that CO2 from Snnipe 70E and the driver was building up inside the car, going back to regular pushed it out.

Also of note, those vents in the back make it easier to close the doors. They keep the car from getting pressurized and pushing back when you close it (large walk-in freezers and coolers have something similar).