# Sauna physics

I spend about 20 minutes in the sauna after my workout, and there’s inevitably the grandson of a Finn who claims he sat in the sauna with his grandpappy, and they got the temp up to 260 degrees!
Today, not only were there several claims of temps well over 200, but that throwing water on the rocks actually lowers the room temp, and throwing hot water on the rocks gets the room hotter faster (I know, conflicting statements, but from different people)
I tried to explain that the water removes heat from the rocks and distributes it into the air as steam, but the one guy kept saying that even though it seemed hotter, it was actually getting cooler.:rolleyes:

Anyway, I think I know how this works. The water cools the rocks, the heat has to go somewhere, and it does, into the air as steam.
But, does anybody know, is it possible to get the temp up as far as 260 (F), and could a human stand temps like that for more than a few seconds?

I am not a fizzycyst. Picture Richard M. Nixon momentarily. Okay, enough of that. I’ll let somebody else deal with the hot rocks, hot/cold water stuff. Thermometers, though, are pretty dicey instruments. If the glass tube slips in the metal housing, you can get a hotter-than-real reading. If you get a bubble in the mercury, you can get a hotter-than-real reading. Even with the painted-on-the-tube numbers, there are variations (sort through the bin to get 2 or 3 with the same reading.) Besides, even though your Finnish friend trusts his grandfather to tell the truth, should you?

Recommended suana temperatures range of to 212 degrees. It wouldn’t surprise too much that some people would go even higher than this range.

Dropping the water on the rocks will cool the room. It will feel hotter because of the humidity. The room will only cool off for a short while by watering the rocks though.

Water does remove heat from the rocks by absorbing it into the water. Also, the phase transition from water to steam will remove alot of heat from the rocks for as it requires alot more heat per unit weight of water to add that last degree of temperature than all the degrees before turning to steam. If the rocks are cooled off, they will heat the air less. The air will cool off (some), but not alot, and won’t last long. The raised humidity will more than make up the difference in how it feels.

I say dropping the water on the rocks would HEAT the room, rather than cool it. If dropping the water on the rocks cools the rocks, where did the heat go? It went into the water, and further, into making the steam. The steam then carries the heat from the rocks into the room, thus heating the room. Not knowing much about saunas, I would think that these rocks are heated electronically somehow (no? I would think gas heating to be a poor idea in an enclosed space like that :eek: ). If that is the case, the heat is most likely controlled by a thermocouple feedback system of some sort. THAT being the case, the thermocouple would notice the reduction in rock temperature, and cause an increase electrical output to the rock heating elements.

So… you would have an immediate (relatively) spike in room temperature from the water carrying the heat from the rocks into the room, and an overall increase of electrical output to the rocks since they cooled down.

The water will cool the rocks. The water turned into steam is not the same temperture as the rocks were. You have forgotten about the energy it takes to boil the water into steam. The energy is not transfered as an increase in water temperture, it is used for the phase transition.

If you pour a bunch of 100 C water on a rock that is at 150 C, the water boils into steam, the rock gets cooled to 100 C and the steam comes off the rock at just above 100 C. Over all, you have cooled the rock without heating the air so until the heating element has a chance to rewarm the rock, the room temperture will fall.

Actually, I’m COUNTING on the phase transition energy to heat the room. That same energy that it took to transition the water into steam will be released upon the condensation of the steam into water droplets (which will happen rather quickly, unless the atmosphere is 100C or greater (in which case I wouldn’t want to be in there)).

On top of that immediate increase in temperature, the long term (say, the next hour) heat output from the rocks will increase as compared to unmolested rocks, due to the heating controller trying to keep the rocks at a constant temperature (assuming the rocks are heated this way).

Actually, I may see our tripping point here. I’m assuming the atmosphere in our sauna is under 100C. If you are making the assumption that the atmosphere is over 100C, what you are saying is correct. But, to answer part of the OP, I don’t think anyone would want to be in a sauna that was 260F. You’d be effectively getting cooked with steam. I’m no doctor, but I would be willing to give my D_Frag guarantee (for whatever that’s worth) of blistered skin.

Putting water on the rocks will definitely cool the sauna. The reason it feels hotter is because of the increase in humidity. The only reason you don’t die a quick death in the sauna is because a sauna should normally be dry. The dry heat will cause you to sweat, and the sweat evaporating on your skin actually cools you down.

The hottest saunas I have been in have been at about 90C. If you entered a room that hot with a high humidity, (or god forbid the humidity at or near the saturation point), you would be scalded! That is the reason a turkish steam bath always have temperatures around 40C. The higher humidity when you put water on the rocks, slows down the evaporation of your sweat, therefore making you feel hotter.

In Germany they like to do something in a finnish sauna called an ‘Aufguss’. Basically they put water mixed with various aromatic substances on the rocks and then spread them throughout the room by waving a towel. After about ten minutes of this, you definitely want to leave that room!

The effect of a good sauna is actually to increase the body’s core temperature slightly (in other words, you’re actually giving yourself an artificial fever). That is why you should first relax for a few minutes afterward and then shower with cold water (do not, i repeat, do not shower with warm water!), or enter a cold water tub. This will then lower the core temperature and give your cardio-vascular system a really good workout. Then, RELAX!!! Take a nap. Anything. But do not go into the sauna again until about an hour later.

I don’t know about anyone’s granddad, but I have myself been in suanas with 260F temperature. Even if the thermameter is a bit skewed, it’s still way over 212F.
I don’t like them. It’s too hot. But there are really people who enjoy them. Adding steam by throwing water on the rocks is a bit of adding insult to injury.

I guess you have to be from our nordic countries to enjoy this torture. BTW, the finns really do slap themselves with twigs of birch and roll around in snow, nekkid, after. No myth. Truth.

Check out this. It’s in English.

Well I don’t know about the twig part but I have used such methods to go swimming in the winter outdoors and it is far from torture. Well THe initial feeling of jumping into the water is a little but once your swimming around - it’s a really strange feeling but a good one. YOu know the waters F&%\$#n freezing and you can feel it is cold water but it is not uncomfortable in the least.

That steam/heat/spiritual experience from the rocks is called “löyly,” pronounced by twisting your lips into a sort of “leuw-loo” way. In a really good sauna, I’ll use a wet wash cloth over my mouth to keep from breathing too much spirits.

/aside

I have observed the same effect when jumping into a cold bath after watching a Kylie Minogue video.

You believed the stories a coupla Finlanders sittin’ in the sauna told you? Did they tell you to watch out for snowsnakes, too?

hahahhahaha! (jk!)

The humiditiy in a sauna even after watering the rocks is low enough and the temp is high enough (sometime higher than boiling) that there will little or more likely no condensation.

If the water was recondensing in the air, I would agree with you.

Good point about the lack of condensation scotth. I hadn’t thought that through properly when writing my last post. I’ll chalk it up to a late night with my 2 week old son . But, if the atmosphere in the sauna is under 100C, adding 100C steam will increase the temperature of the atmosphere in the sauna regardless of condensation. In this scenerio, we’ve still added a 100C gas to an atmosphere of <100C gas.

If we are talking about a 260F atmosphere sauna, I have little doubt that adding 100C (212F) steam to the atmosphere will cool the atmosphere in the sauna.

Honest to goodness Finnish-American chiming in: the bundle of birch branches used to slap yourself or others with is called (in Finnish) either a “vasta” or “vihta”, depending where in the country you’re from. And for me, the thermometer usually reads 215-220 degrees F – though I can usually take no more than 15 minutes of this at a time. This is for electric stoves; wood-burning stoves usually reach lower high temperatures.

I have been in 120 degree C saunas, and although the dry heat is bearable, I did not find it pleasant. To me the ideal sauna temperature is around 90 C, you can sit back and enjoy the experience for 20 minutes without becoming overheated. I also like rolling in snow after a good stay, the weirdest feeling comes when you go back in the sauna and the snow melts and runs down your back! Throwing water on the rocks lowers the overall temp., but the blast of steam feels hotter because steam conducts heat better than dry air. When you use a vasta to beat yourself, your neighbour in the sauna gets the worst of it due to air currents.
Believe it or not, I was BORN in a sauna in Finland 52 years ago.
My parents never told me if I was conceived in a sauna, too?

The old Finns and Norwegians at home (MN) always liked their saunas in the mid 200’s F. I couldn’t hang with most of them. Mainly because they thought it was fun to lean over and breathe on your shoulders while you were wilting. It felt like your skin was melting off.

Like Finnie we kept ours at home around 200, which was perfect. But I gotta agree with how good it felt to go from 200’ish F outside to -40F and dive into the snow until you couldn’t take it anymore and then race back into the sauna. Do that a few times and it was better than sex. You just felt GOOD when you were done.

It’s gotta be hot and hotter the better. My Mom was born in a sauna like million of Finns before her. Minnesota Sauna nights were always kids and moms first, singles and the old folks last in because that was when the temp was at its best.

I don’t remember the actual temperatures, but this might give you an idea. I used to take sauna every Tuesday night in Khartoum, Sudan… yeah, where daytime temps can climb on average to 116. Some Finns working on a development project asked a friend if they could build a sauna in his backyard for their use on Saturday nights. Tuesday nights my friend would have his friends over for beer and sauna [this was in the late 80s before the radicals grabbed power]. We would step out of the sauna to cool off, drink some water and go back in until clean…beer was for the final cool-off. The sauna temp seem so much hotter than the hot, dry night air in Khartoum. I remember those sauna nights with fond feelings.

All right, I’ll bite:

What is the point of baking oneself in a sauna?

Historically, it was for cleaning oneself. My family, like many in this area, has a sauna at our ‘camp’ - our cabin in the woods. There’s no plumbing, so if you want to stay up there for several days at a time you need to clean yourself somehow. It might not seem like it, but sweating in a hot, steamy room really does get you clean. I feel cleaner after a sauna than I do after a shower.

To some, saunas are social things, too. As many have detailed above, the Finns and other Scandanavians think of saunas as many of us nowadays think of hot tubs.

Third, saunas are relaxing. The ideal sauna has benches long enough to stretch out on. They’re as good as a massage.

Another note - for those of you who think of a sauna as that hot, dry room found off the swimming pool in most hotels, that’s not at ALL what a real sauna is like. Finnish saunas are not dry. You put water on the hot rocks and get a good steam going. Most that I’ve been in are fairly large - like I said above, you want benches long enough to stretch out on. Wood fired, IMO, are the best, but electric are pretty good as well.

Pronunciation: Sow-na, not Saw-na. At least that’s how the Finns in my neck of the woods say it.