What is the origin of 72 degrees and 'room temperature?

October 16, 2011 4:34 PM

Does anyone know how or why 72 degrees fahrenheit was decided as the ideal ambient temperature for humans? is there any scientific basis for this number at all? seems like it makes sense, but why 72, instead of 73 or 71? any ideas when, where, how or why this came into practice? Thanks! /bc
posted by quickasfoxes to Science & Nature (21 answers total)

I question the premise of this question. If someone put a gun to my head and asked me to give a number, I'd say "I don't know? Somewhere between sixty and eighty?" and if they then squeezed the trigger I'd probably say seventy. Because it's round. But I don't think 72 is universal. In any case people dress differently in different seasons, so the ideal temperature can't be the same year-round unless you never go outside.
posted by madcaptenor at 4:43 PM on October 16, 2011 [1 favorite]

72*? I've always heard 68*.
posted by NotMyselfRightNow at 4:46 PM on October 16, 2011 [3 favorites]

I've always heard that it was 72 degrees, (or 21 celsius), and apparently lots of other people have heard that too, and wondered the same thing. According to Google Answers, the reason is "that the ideal temperature for minimizing asthma and allergies, preserving cigars, maintaining cut gerbera daisies, serving wine, and growing marijuana (!) is 72 degrees!", and according to Wikipedia seems to indicate that while it isn't a scientific measure, that its the generally accepted most comfortable average temperature across seasons.
posted by Kololo at 4:54 PM on October 16, 2011

Its not a universal thing. But its a temperature that we think we can make about 80% of the occupants happy. See the artical on thermal comfort. There are also a ton of other factors like radiant temperature, air speed, and humidity. There is also a factor for how much clothing the occupant is wearing. It has a unit of "clo". So ASHRAE has put some research effort into this.
posted by ihadapony at 5:03 PM on October 16, 2011 [1 favorite]

As a scientist, when I see "ambient temperature" in a protocol, I assume 68 degrees Fahrenheit, and I had always assumed that it was chosen based on how it is equivalent to the nice round 20 degrees Celsius (or rather 20C had been chosen and translated to Fahrenheit). I also often see ambient as a range of 68-72 degrees, which again is the nice round range of 20-22C in the metric system. But I can't really cite this...
posted by Tandem Affinity at 5:05 PM on October 16, 2011

I'm Australian. When I did first year science in 2005, standard ambient temperature was considered 25 degrees celsius or 77 degrees fahrenheit at 100 kPa or 14.5 PSI.

I just did a quick look on Wikipedia and it seems that Tanenbaum was right - "The nice thing about standards is that you have so many to choose from".
posted by dantodd at 5:20 PM on October 16, 2011 [2 favorites]

I've always heard that it was 72 degrees, (or 21 celsius),

21C is 69.8F. 72F is 22.22C.

I hadn't heard the 72F thing, but the fuel poverty definition in the UK suggests not being able to afford to heat the main living space in a domestic dwelling to 21C is an issue.
posted by biffa at 5:30 PM on October 16, 2011

Sorry, that should have been 1995 not 2005.
posted by dantodd at 5:34 PM on October 16, 2011

To my (midwestern-US-reared) mind, 72 degrees F is indeed "normal room temperature". My initial guess would be that it's because Imperial measurements are a base 10 / base 12 hybrid, and 72 is divisible by 12, making 72 a natural point of reference.

The Wikipedia article on Fahrenheit is related and interesting. (Though of course as a science article on Wikipedia it may or may not be made up.) It doesn't touch on the room temperature question directly but does note that originally the ends of the scale were conceived as the freezing point of a particular brine (0 degrees) and normal human body temperature (96 degrees).
posted by tivalasvegas at 5:34 PM on October 16, 2011

Hmm. I always thought room temperature was 75 F.
posted by limeonaire at 5:54 PM on October 16, 2011

Found this in The Louisville Monthly Journal Of Medicine And Surgery, Volume 21 № 3, August 1914, p. 85:

During the period 1825 to 1875 the standard of temperature of dwellings and public places was gradually increased from 55 degrees F. to 72 degrees F. There was no attempt at corresponding increase of humidity. Fifty-five degrees with natural ventilation implies about 40 degrees relative humidity; 72 degrees F. gives a natural humidity of 20 per cent, or lower. From the health point of view the 20 per cent, decrease in humidity is more important than the 15 degrees rise of temperature.

Catarrhal and acute infections are more prevalent during the cold months to a degree not credible. Abnormal dryness of the air of our habitation is a factor worthy the attention of hygienists. Dry air is a dust ladened air—and an infection disseminator. Moist air causes precipitation of dust content, and a proper humidity lessens dangers of air borne infections.

And then in The Laryngoscope of the American Laryngological, Rhinological, and Otological Society, Volume XXIV № 8, August 1914, p. 751:

Fire was man's first friend—that is, conservation of body-caloric by artificial heat started the evolution of the higher nervous system, but, to carry this logic to an absurd extreme, one cannot say that mental precocity is in direct relation to the ingenuity in inventing and utilizing heating apparatus. Based on this theory the inhabitants of the Northern and Middle States might claim, for instance, that they are at least 10 degrees more progressive than Europeans. Heating and ventilating contracts in public school buildings specify 70 degrees in America, and in England 60 degrees. They might raise the question as to which temperature-standard favors the more rapid expansion of the intellect. Are we really 10 degrees hotter on the trail of Truth?

It is interesting to follow the gradual change that has taken place in our own country during the past half century in artificial heat standards. In 1820, American text-books gave 50 to 55 degrees F. as the healthful, comfortable temperature of the living room and nursery (and I should add in passing that the natural relative humidity, taking into consideration the methods of heating,—luminous heat and direct radiation, the open fire-place, ovens and the Franklin stove—would probably be about 40 per cent. In 1850, the comfortable temperature was stated to be 62 degrees F. and in the next thirty years it was raised to 72 degrees F. Now should we consider this 17 degree change (55 to 72) a triumph of man's increasing dominance over the elements, or are we on the contrary 17 degrees decadent in physical vigor? Our ancestors of two generations ago would have considered 72 degrees the proper temperature for the aged and infirm, but not for youth. This whole record is a commentary on ingenuity in invention and extravagance in burning up natural fuel resources. (The base burner and hot air furnace were invented about 1840.) Again I must mention humidity in this connection. The moisture in the air of a building at 70 degrees F., (this applies particularly to public school buildings and places of sedentary employment) would naturally be below 25 per cent relative. Therefore, if we were to state that in the period from, say, 1825 to 1875, we reduced the standard of humidity from 40 per cent or 50 per cent relative to 25 per cent or less it would be a more significant fact from the hygienic standpoint than to call attention to the 17 degrees increase in temperature during that period. In other words, we have worshiped a false god of comfort,—Fahrenheit. Rather too mercurial!

Both by the same guy, one Thomas Hubbard, MD.
posted by XMLicious at 6:27 PM on October 16, 2011 [5 favorites]

AFAIK, this is based on SCIENCE! tied up with human efficiency studies that date back to the turn of the century. The ASHVE scale from the 20's identifies a small range of temperatures & humidities that people feel most comfortable at under different physical stresses. IIRC ('cos I can't dig up the original paper now), that range is 68-72°F.

I always assumed, without any particular reason, that some industrialist (Ford? He was into that sort of thing…) settled on 72°F as maximising efficiency while minimising cost, and everybody else followed suit.

Googling "thermal comfort analysis" throws up a bunch of studies that look interesting for further research.
posted by Pinback at 6:42 PM on October 16, 2011

(Oops - that should be "a small range of temperatures that maximise comfort under a range of different humidities and physical stresses".)
posted by Pinback at 6:44 PM on October 16, 2011

Yeah, not to dogpile but it's absolutely not an absolute (ha). When my classroom is set at 72F, half of my students are FREEZING and complaining, a quarter are fine, and a quarter are MELTING and complaining. For most of the students, that's simply not a temperature setting that they're used to. (My students are not North American.) Nonetheless, XMlicious' and Pinback's answers are interesting. :)
posted by wintersweet at 7:41 PM on October 16, 2011

More info:
Comfort zone for air (~ ½ way down) - 72°F / 22.something°C looks to be smack-bang in the middle of (presumably US-centric) summer & winter optimums over 30-70% R.H.

PLEA Note 3 : Thermal Comfort - The history section is interesting, while the rest includes some explanation and discussion on the ASHVE index and later models.
posted by Pinback at 8:16 PM on October 16, 2011

65 degrees, if you're Jimmy Carter... which is to say, there's no one ideal.
posted by The corpse in the library at 8:22 PM on October 16, 2011

(Last one, I promise ;-)

Climatic Discomfort in The Kimberleys (1959) - a bit of historical scientific management. "Climatic discomfort lowers the efficiency of the work force, thereby reducing output per head … Monotony of climate is an important subjective factor influencing discomfort, and therefore human efficiency."
posted by Pinback at 8:40 PM on October 16, 2011

I had also always heard the 72 degrees figure was preferred as it was optimal for office productivity. Apparently, studies show slight variations but a range from ~72 to ~77 seems to work.
posted by misha at 10:40 PM on October 16, 2011

Every single integrated circuit I know of specs its parameters based on tests at 25C. Hence, I've come to calling that nominal room temp. I figure if it's good enough for Intel, Samsung, Hitachi, Motorola, RCA, Dallas Semiconductor, Texas Instruments, Analog Devices, Sprague, ad infinitum, it's good enough for me. Never bothered to ask where it came from, but it certainly is homogeneous across electronic components, FWIW.
posted by FauxScot at 4:16 AM on October 17, 2011 [1 favorite]

In my office, there is no acceptable temp that satisfies everyone, and preferences change daily. My preference, then, is to use the most energy-efficient temp. Our system will allow me to set it as low 69.5 heat in winter, and I forget the summer temp range. People can actually adapt to a pretty wide range of temps. The more Central A/C and heat we have, the less people seem to adapt, in my experience.
posted by theora55 at 8:07 AM on October 17, 2011

70 to 75 was the avarage temperature range in the highlands of East Africa when I lived there so I think we simply like the temperature we evolved in. I've tried to find out the temperature in that area 100,000 to one million years ago, but with no luck so far. Does anyone know?
posted by nickji at 12:52 PM on October 17, 2011 [1 favorite]