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Rick;
Didn’t you ever hear of the old wive’s tail that hot water in the ice cube tray freezes before cold water?
You have to look beyond Physics and study Heat Transfer. Raising the temperature differential will set-up a highly efficient condition known as “forced convection” cooling. Small air currents will circulate the cool air aross the warm surface. These currents will continue until the temperatures are nearly equal. Cold water also starts the forced convection, but it is usually too weak to be sustained.
Even the hose bib on a hot water line can loose heat faster through the convection cooling than can be supplied by heat conduction through the water & water line.
Exterior faucets should be frostless sill cocks NOT standard hose bibs. The shutoff is actually well inside the house away from the cold outdoors. It also helps if sill cocks are not the last on the lines.
cheers; JE
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Rick;
Didn't you ever hear of the old wive's tail that hot water in the ice cube tray freezes before cold water?
You have to look beyond Physics and study Heat Transfer. Raising the temperature differential will set-up a highly efficient condition known as "forced convection" cooling. Small air currents will circulate the cool air aross the warm surface. These currents will continue until the temperatures are nearly equal. Cold water also starts the forced convection, but it is usually too weak to be sustained.
Even the hose bib on a hot water line can loose heat faster through the convection cooling than can be supplied by heat conduction through the water & water line.
Exterior faucets should be frostless sill cocks NOT standard hose bibs. The shutoff is actually well inside the house away from the cold outdoors. It also helps if sill cocks are not the last on the lines.
cheers; JE
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Rick: I've encountered that old-wives tale (p.c. version: chronologically gifted spouse's anecdote) and it's all a bunch of hooey. Of the course the hot water cools faster initially, but once it's at tap temperature, it will cool at the same rate as tap water (but will always lag by that initial cooling time). Any convection currents set up initially will dampen out quickly. If you stir the air in the freezer with hand and closed the door, it won't keep swirling around in there for many minutes.
Some of this is being discussed under the "Avoiding Frozen Pipes" discussion.
They make those freeze-proof hose spigot valves in several lengths for different wall thicknesses, get the deepest one you can fit. I'm putting all mine through where an interior wall meets the exterior wall. So I can use very deep recessed valves and so I've got no standing water in any exterior walls. I'm also going to slope mine down at the very end to make it more positively draining.
I've got a dog musher friend in Kasilof who spec'd hot and cold freeze-proof recessed faucets (his 26 dogs get a hot gruel mixture each day and he can mix it all outside). Really nice to have a hot water spigot in the backyard for washing the dog, kids, and equipment!
A little heat tape, installed in advance and left accessible but unplugged can be a blessing when problems crop up.
The totally bomber (safe) way to keep it from freezing is to put those recessed spigots on a thermosyphoning loop of hot water. This assumes that your hot water is below the spigot. Run piping up from the heater, to your various fixtures and faucets and back to the cold inlet of the heater. Inslulate the shole loop and put in a swing check valve. Not only will the loop always be hot and therefore conduct some heat out towards the spigot, but you'll have instant hot at all your fixtures.
Getting from the neighborhood,
-David, Kenai, Alaska
*Well here's a twist on the explanation. Is it physics or groundless folklore?Temperature is a measure of degree of heat (like volts with electricity). Calories (or BTU's) are a measure of volume of heat (like amps). The hot water is less dense, it has less mass even though it has a higher temperature it may take fewer calories of heat lost to reach freezing point.I would guess the relationship of volume, absolute water start temp, ambient temp, rate of transfer (convection, conduction, area of exposed surface, etc. etc.) all play a role.Does it ever happen? Sometimes? Where is Bill Nye or Mr. Wizard?
*Duh...as the warm water cools, does it 1) retain it's original density, 2) become more dense and create a void space, or 3) become more dense and due to the system being pressurized have that potential void space replaced with water from upstream? This is real rocket science.Brian
*As a side note, I have found that the modern freeze-proof hose bibbs also have anti-siphoning devices in them. It's been my general experience that these devices can be responsible for most of the noise from the bibbs and, if they're removed for cleaning and not re-installed, the noise goes away. There shouldn't be danger from siphoning if you don't keep a hose attached to the bibb when not in use, if you don't leave the hose in a kiddy pool, and if you don't have a flood.
*Barry,You've got a healthy attitude towards safety. If a safety device is inconvenient, get rid of it. Anti-siphon hose bibs are designed to protect the water system, not for "if you don't" but for "when you do." Not under normal conditions but under adverse conditions. There shouldn't be danger if the water supply is not turned off either. But when it is, contaminated water can be syphoned back not only into a house, but into a public water system. That shouldn't be a problem either if the water is not too badly contaminated, but when it is, a lot of people can be exposed to nasty things like hepatitis. But in the meantime you don't have to listen to noisy pipes.
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This reminds me of a story I heard about a friend of mine. This man is a renowned sea ice scientist who was in Washington attending an environmental working group chaired by our VP Al Gore. My friend, because of his stature, ended up sitting next to Mr. Gore. During the proceedings, the Vice President turned and asked, "Is it true that a like amout of hot water will freeze before cold water?". My friend, always outspoken, replied, "Mr. Vice President, don't be stupid!". Mr. Gore then turned and the meeting continued.
tf
*I'm surprised that this entire thread is lacking the true explanation that I learned in school. Idle hot and cold water pipes at the same ambient temperature: the hot always freezes first. Anything disolved in water lowers it's freezing point, including disolved gasses. The heating and storing in your hot water tank dissapates much of these disolved gasses and this is why it freezes clearer and more easily. Plumbers here up north know this from experience, if not the exact reason why.
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If the water in my hot water bibb freezes and cracks the metal housing, but noone is around to actually hear it crack, does it really make a sound?
Brian
*Mike,Thanks for your thoughts. I am a prudent person, always safety conscious, use GFCIs and all of the normal noxious chemical detection devices, etc. etc. Civil disobedience isn't my style. But if they want me to retain the anti-siphon devices, then they darned well better make the &^$@#%$^ things so they're quiet!! Not too much to ask, I'd think. I categorize these obnoxious devices with the 1974 seat belt interlock. When I was a helicopter pilot in Vietnam, I was concerned for the lack of redundancy in vital systems, the lack of armor, insufficient firepower, and no parachute. The answer was that if you provided for every contingency, the thing was too heavy to get airborne. Just fly safely, elude the enemy, shoot accurately, and don't get shot down. I'll be careful about disconnecting my hoses.But since we're playing Mr. Wizard, how come there's little fizz when you put ice into warm Coke, but tremendous fizz when you pour warm Coke over ice? I've, of course, only observed this phenomenon with others, as it doesn't do the same thing with my scotch.TIA.
*Hot water freezes first (contrary to common sence), although the physics are complicated and I don't remember the details. I saw a link, I think it was on the Plumbing Forum, that had a long discussion by a university professor, at his site, of how the physics actually works.By the way. The new IPC, International Plumbing Code, is supposed to require seperate shut-off valves at each outside hose bib. It seems rediculous (sp?) to require this in non-freezing climates, but despite proposed ammendments, they are doing it. If you have a basement, you'd put the shut-off valve there, but if you don't where do you put the shut-off valves, outside? It might just apply to commercial.
*Barry: I too find it a little hard to get all excited about anti-siphon valves. Sure, I put them in, but I don't get up on a high horse about it. The remote chance that I'll drink some kid's piss, diluted about 100,000:1 from a wading pool that had a hose left in it, during a water system failure, that drained the system below the level of the kiddie pool, when the hose had no air leaks in it that would break the siphon, etc, etc, doesn't keep me up nights. I think the bigger danger is that someone can so easily inject something really nasty through any house or public drinking faucet. So why aren't there check valves on every water service as it leaves the main? Maybe because those retrofits would cost water companies some real money. So instead, protection (anti-siphon valves) against this piddly chance of exposure to a piddly amount of piddle is required of every homeowner or contractor doing a remodel or new construction.Re fizzing cokes: two phenomona here. One is the solublity of CO2 in water and the other is nucleation. The solubility of gases in water is higher at low temperatures. That's why there are more kg of fish per cubic meter in the arctic (pollock, cod, halibut) than the tropics (cute and colorful, but small or spread out) - less CO2 and O2 supports a less dense food chain. So the warm coke, fresh from its pressurized can is even farther from its equilibirum and gives up its CO2 faster than a cold coke.Nucleation: when materials change phase (liquid to solid, liquid to gas) it happens most quickly in the presence of some material that allow ice crystals to form or gas bubbles to develop. That's why cloud seeding is sometimes done and why "boiling chips" are added to boiling liquids in chemistry labs. Otherwise you supercool and superheat liquids (by a few degrees). Arctic ground squirrels hibernate a bit BELOW 32F because they don't have any chemicals in their bodies that allow the ice crystals to form.Note that once a coke has been poured over ice cubes and fizzed a lot, the same ice cubes won't cause much fizzing by the next coke. Most the rough surfaces (both visible and microscopic) have been smoothed off and it is not as good a nucleation surface. -David
*Good Gravy! how could a post on hot hose bibs command this many reponses? Are we okay?
*First, I apoligize to both myself and others for getting sucked into this debacle. I thought this thread would die soon, now I'm assisting with the CPR!In a sense, BOTH arguments CAN be correct. I think I just threw gas on the fire. Most of the pertinent facts have already been brought forth by others.The first two posts lay out the main facts. Mike and Greg both bring forth that water, straight from the source (private well or city main) has both soluble and insoluble particulate in it. One branch goes to the cold water tap. The particulate remains suspended/dissolved. The other branch goes to the hot water heater. As the water is heated, it gives up dissolved gasses. While it sits in the tank, suspended particulate drops out to the bottom of the tank. We all use more cold than hot water during the day, so the cold "impure" water is constantly being replenished, the hot is given additional time in the tank to "purify".Pure water, in a pure environment, freezes at approx 32F/0C. Add impurities and the freezing temp is lowered. The amount lowered depends on the amount and type of impurity. On the same note, water can also be supercooled to well below the freezing temp while remaining liquid. The limit, suprisingly, is -40F/-40C. I won't touch that here, though.To the other extreme, water with no impurities, in a sterile vessel with no surface flaws, will not boil until superheated. It needs to go up to approx 230F/110C. As it boils, it gives up heat, dropping down to the familiar 212F/100C figure, then boiling stops and the cycle repeats. Add a few scratches or flaws to the inside of the vessel and the boiling point is reduced by a few degrees. The irregularities in the vessel surface allow minute steam bubbles to form. Once formed, they quickly grow, then rise to the surface. Add impurities to the water itself and the boiling point will be lowered by a few more degrees. The next time you make pasta, just as the pot is starting to boils, throw in some salt. You've just lowered the boiling point of the water and the water should go to a vigorous boil since it's superheated. As it boils, it will carry off heat, eventually reducing to the impure boiling temp and settle into a comfortable boil. Dave mentioned boiling chips, small ceramic chips added to liquid to break the "boiling cycle" mentioned above. They act as flaws in the vessel, so to speak, and help promote an even boil. Anyone own one of those "boiling rings", they are sold in department stores. You put them in a pot of water and they help the water to boil faster? Same idea as a boiling chip.So, impure water both freezes at a lower temp and boils at a temp lower than pure water. For the discussion below I'll consider water that's been through the water heater to be void of air bubbles and suspended particulate, thus "pure". Water from the cold tap willl be "impure".Apples and Oranges: Two ice cube trays. Take water from the hot water tap (120F or so?) and place it in one tray and put water from the cold tap (55F?)into the other tray. Were you to put them in the freezer, I would think the cold would freeze first, due to the initial temp advantage. It does depend on the types and quantities of impurities in the cold water and to what degree they depress the freezing temp of the cold water, but the cold water should freeze first.Apples and almost Apples: Now repeat the process (hot water tap in one tray, cold water tap in the other tray), but let the water in both trays come to room temp prior to placing tin the freezer. In this case, "pure", previously "hot" water should freeze before the impure, previously cold water, due to its higher freezing temp. Once frozen, compare cubes. The "pure" water should have clearer cubes. Apples and Apples: Fill a tray from the hot water tap and let is come to room temp (70F?). Now, fill the other tray with HOT water (120F?) and place both in the freezer. The room temp water will freeze first. Same water, same freezing temp, just different initial temps.Back, for a moment to the clean ice cubes and previous posts. These "cleaner" cubes also have the advantage of having a smoother surface, thus they are less likely to cause your carbonated beverage to fizz as much as cubes made from "impure" water. The microscopically rough surface of the ice cube acts just like the flaw on the vessel surface. It's a catalyst to bring the gas out of solution. Want to reduce the fizz with dirty cubes? Rinse them in water. The warm water will melt minute surface irregularities resulting in fewer bubbles.For this reason, I have the water line to my ice maker tapped off the hot water line. Am I sending hot water to my freezer? No, as the water sits in the supply run and cools to ambient temp long before entering the fridge. Same idea as adding an in-line filter to remove impurities to get "clean" ice cubes. In this case, the water heater is my "filter." There is a difference in cubes. Try it.Does hot water freeze before cold water? Not if it's the same water. Does water directly from the hot water tap freeze before water from the cold water tap? Possibly, but I'd doubt it. Depends on the initial temperature difference and the difference in freezing temps, but on average, I'd wager that the cold would freeze first. However, if starting at the same initial temperature, water that has been through the hot water heater will most likely freeze before water that has not. Sorry if I muddled the issue. Not trying to foster an argument, just trying to clarify based on how I perceive the topic. I still have many "possibly's", "maybe's", etc, but hey, it's a house and not a laboratory, thus an uncontrolled environment. .Time to go to the pantry for some Guiness and Tostitos...Mongo
*I repeat. HOT WATER FREEZES FIRST.See: http://math.ucr.edu/home/baez/physics/hot_water.html From the discussion "hot water to ice maker" on the Plumbing Forum. There is a link to the Plumbing Forum at our web page.Gary Wheeler, AIAweb page: http://home.att.net/~g.wheeler
*Gary, I checked out the site, thanks for the referral. The Mpemba Effect is one of those things that many people take and apply haphazardly in an across-the-board fashion. It is based on a quantity of water with a fairly large surface area exposed to the atmosphere. It also considers the water in a vessel, typically wood, which has some insulating qualities and a rough surface. It doesn't fully apply in this argument.In the professor's own words:"Although research has been done on some specific cases where hot water freezes faster than cold, the experiment has...not been studied enough in detail to establish the conditions for it to happen. The answers given here should not be considered difinitive..." That's backpedaling, nothing wrong with that, just a disclaimer...He explains the five factors that contribute to his theory:1) "Evaporation...is important when there is a large exposed surface area. " Zero, inside a copper pipe. "Mass is carried off so that less water needs to be cooled." Zero inside a pipe. "Also, the temperature drops due to heat lost in the phase change from liqiuid to vapour." Once again, zero.2) "Supercooling...some experts believe it is the most important factor...however, most of these experiments have been carried out in ideal experiments...it is not clear how well they represent the classic case..." Theory.3)"Convection...it would be neccessary to show how hot and cold currents are separated in the process...no experimental evidence has been found to support the hypothesis...". No evidence to support...4)"Dissolved Gases...is often cited as an important factor but no references to experimental evidence or quantitative analysis has been given up." No evidence to support..."5)"Conduction...This final mechanism is more relevant to the case where water is placed in a freezer in small containers." I find it difficult to read this report and come to a blanket conclusion. There are quite a few references from other professionals, both researchers and educators, who support the other argument. Neither side has definitive, hardcore evidence that applies to ALL CASES. In copper plumbing this argument falls by the wayside, as the professor's most important point is exposed surface area and the resultant evaporation of mass, meaning there is simply less water left behind to freeze. Non-existent in a replenished copper pipe. Two little-used domestic water branches, one hot, one cold. If niether is used for a while and the water in both is at the same ambient temp, in a freeze yes, the hot may freeze first. With a frequently used hot water run that is at 120F, I seriously doubt that the hot would freeze first. I stand by my previous conclusion. I'm not calling you wrong, I'm just saying that your evidence fails to persuade me. Last year my daughter's class argued the same issue, each child went home to run the experiment. Every child got the same results in the hot and cold at room temp. Hot froze first. They all came to the same in the hot- hot and the room temp-hot as well. Room-temp hot froze first. The same with the last, the hot-hot and the cold-cold...the cold-cold froze first. Not scientific, and not in copper pipe, just a fun experiemt for the kids to do. Once again I believe sometimes it does, sometimes it doesn't...with hardcore beliefs like that, I should go into politics...Waveringly, Mongo
*Mongo, If you are crazy enough to get into this, so am I. Furthermore, I agree with every word you said. I also have my ice cube maker hooked up like that for exactly the same reason. It was a slow evening last night so I broached this subject with my wife. Using your theories and that of my old college chemistry professor, I conducted a semi-scientific experiment outside in the 10 below zero night air.I filled two identical containers to the same level with water at 40 degrees and water at 120 degrees (the source for each was from the hot water tank). I set them out and observed that the cold water did indeed freeze first (by about 45 minutes). Now I'm more worried about my water line freezing!
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Jeez, Mongo, your two posts nailed that puppy down tight. Nice!
*Sounds as though you just might have a good grounding in what is called the "scientific method". But going with this post any further would be like fighting windmills...
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And I quote from my Webster's New Collegiate (not even a chemistry book or an unabridged), "Nucleate vt, 1: to form into a nucleus : CLUSTER 2: to act as a nucleus for, etc." It may sounded confusingly like "nuclear energy" or "nuclear bomb" as when physicts are referring to a nucleus of proton and neutrons. But as chemists use it, it refers to a nucleus of molecules of a specific phase (e.g. the steam or ice phases of water).
*G: I too thought too many people were theorizing when the way to test the theories was obvious of easy. I started with 42F (cold tap) and 150F (heated hot tap) water, and put identical amounts in two shallow tupperware container and placed them outside in the 14F (not a very cold day) weather. The hot water dropped very quickly in temp (in 17 miuntes the cold and hot were 33F and 64F, respectively) and the hot water approached the temp of the cold water in an hour. At one hour and 40 minutes both were 32F, the cold water a thick surface of ice and the hot water had a thin surface of ice. I'll try it again when the weather gets cold. I'm off to the Copper Basin 300 mile sled dog race tomorrow and the HIGHS in Glennallen yesterday were -18F! (low was -35F). Ahh, what we do for science. -David
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I'm not a scientist, chemist, nor master builder but I do know that the hot water lines are the first to freeze in a house. Duh? Is'nt this the basis of this discussion? Why are we throwing around a bunch of craptrying to act like Harvard PHDs? Give it a rest, hot water lines freeze before cold! Who should care except for a few techno nerds?
*Don, I've lived in the land of frozen water pipes all my life and have repaired or replaced them every winter. I too have often seen hot water lines in homes freeze and right beside it is a functioning cold water line. Why does this occur?? Simply because the cold water line was used more frequently and the "hot" water in the other line simply sat there cooling off until it froze. This does not have anything to do with rocket science!The point is, if you run pipes inside wall cavities, through freezing cold crawl spaces or other places like this, you are going to have frozen pipes, both hot and cold. The best way to avoid this is to do everything you can to keep the environment around the pipes above freezing. Heat tapes are a LAST resort for extreme cases. I think they are dangerous.A properly installed freezeproof faucet will not freeze. Keep the shutoff valve inside a heated space, slant the faucet toward the outside so the water drains out of it, and above all...don't forget to disconnect the hose or it will freeze anyway!
*I recall the hot water freezing first phenomenon was explained away in Scientific American a few years ago: A vessel of hot water in a freezer initially melts the ice under it, which then quickly refreezes, thus increasing the effective contact surface area of the vessel and allowing the hot water to cool and freeze rapidly. The cold water vessel usually sits upon an insulating later of ice crystals which will not have the same contact surface area and thus reduces the efficiency of heat transfer of the water. The Sci. American conclusion was that this myth came about because of this specific fault in experimental design. The final note was that given the EXACT same conditions (as as logic would have it) cold water will freeze before warmer or hot water. Try hot water with the old-fashioned metal ice cube trays, and you'll see how this myth got started...and now you'll know why.
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The hot water will freeze quicker because of less disolved air. But does it matter if the hot freezes at 2:15 AM and the cold freezes at 2:17 AM? I don't think so. Use frost proof faucets and don't leave the hose on in the cold. Also get a hose "Y" to mix the hot and cold. Don't bother with heat tape, it wastes energy and the electricity will be out in that ice storm anyway.
*In an uncontrolled unintended experiment a couple months ago the hot water to our upstairs bathroom froze. The wife, who takes showers in the MORNING, was NOT amused.It was unusually cold that week. My explanation to her at the time, was that she had used the toilet in the middle of the night, and that was probably enough water transfer to keep the cold water pipe from freezing. After looking into the physics a little, I'm not so sure anymore.This being California, and having a design temperature of something like 30 degrees F, hard freezes are not usually a problem. The pipes in question are 1/2" rigid copper pipe, outside the wall, but insulated with foam insulation, although exposed to the sun and open at some of the corners etc. The hot and cold are about the same length and location.The next night, we let the faucet drip a little water to keep flow, cracking open the hot and cold valves.
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I am not an expert, but I believe that hot water will freeze faster than cold, but only under certian very odd circumstances. If you take two cookie sheets and put a thin layer of hot water in one and simularily cold water in the other, the one with the hot water may freeze faster than the cold. This is due to a very large surface area when more evaporation can take place in the "hot" cookie sheet. With each molecule of water that evaporates from the hot cookie sheet, it takes energy with it, this amount is known as the "heat of Vaporization", or at least it was when I was in high school, (I am still upset about inert gases now being called noble gases...sniff). The more heat that escapes through evaporation, the quicker the temperature drops. In extreme cases, this means the cookie sheet with the hot water will freeze quicker than the cookie sheet with cold water...but except for an interesting way to spend a winter afternoon, this "effect" means little.
In the real world I think that the two sill cocks would freeze equally as quick (assuming equal use, or rather, lack of use) and if you desire a hot and cold sill cock, why not...
Now watch someone prove me wrong...well...science ain't exactly a science, you know....
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Joe: I guess I misunderstood your question about "Nucleation: when materials change phase (liquid to solid, liquid to gas)", sorry. I didn't mean that that phase change is the definition of nucleation, but rather that foreign particles, rough surfaces, and impurities which facilitate a phase change are examples of nucleation.
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Nucleation and sublimation, fizzing cokes, etc. That was some good stuff! I enjoyed that and the brains behind it all - and the very gentlemanly banter back and forth. Great!
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We were adding an addition and I wanted not just cold, but hot water hose bibs outside!
The plumber looked at me and said nope--- the hot water ones always freeze first. I looked at him and said (as I searched my memory banks back to physics class) go ahead and do it-if it freezes it is my problem.
I thought about it and asked every one I know and they all agree--- we can think of no reason why a hot water hose bib should freeze faster than a cold water one!
Has anyone else heard this?? Is it an "ole wife's tail"??
(So far -- neither one has frozen-- and it gets pretty cold in Anchorage).
Thanks!
*If you take water from the water heater to make ice, it makes clearer ice. The reason being that junk has time to settle out and disolved air is dissipated. So what have we here, but the beginning of an old wive's tale. So it somehow becomes known that hot water freezes faster. Now, in order to justify this myth I have heard people talk some nonsense about evaporation cooling the water quicker. Pretty soon this is accepted as fact. The fact is that hot water will loose heat to a given temperature environment faster as long as the temperature differential is greater, but there are more BTU's to loose. So the cold water will always freeze quicker. As far as hose bibs go, I would suspect that the one that gets used the least will freeze first.