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I want to install a water outlet on the outside of my house for gardening etc. Outside temperatures here in Latvia fall to -25°C sometimes, so I cannot use a common water pipe; it would burst when the water freezes. Is there a formula to tell how thick the pipe wall must be compared to the water volume inside the pipe, so that the pipe would withstand the force of frozen water expanding. Are there water taps that are strong enough?

Are there other solutions that do not require heating?

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would shutting off the outlet in the winter be sufficient? – rpmerf Feb 26 at 12:48
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No, that's too service intensive :) – AndyZ Feb 26 at 13:59
    
Just a note @AndyZ if you have a hose on all 3 of these examples below with the water on they can freeze. The way they all work is by draining the water to the freeze zone and the valve seat is at a warmer location. – Ed Beal Feb 26 at 14:37
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Just for clarification, it is NOT ice that causes the burst. The plugs of ice forming cause a steep rise in hydraulic pressure - up to 250 bar. You can Google the pipe required to resist that! That's why all bursts are flared. They are explosive decompressions. The valve mentioned looks perfect. – YorkshireDave Feb 26 at 15:33
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The common solution in Canada sounds like what you already have: an ordinary valve outdoors with an indoor valve (which is equipped with a drain plug). Simply shutting off the indoor valve isn't enough to prevent damage - the line must be drained by either opening the drain plug or the outdoor valve. – Anthony X Feb 28 at 16:44
up vote 40 down vote accepted

A common device used in the US (and required by some building codes) is a water outlet that is long so that turning off the water allows the portion exposed to the elements to dry out. These are called "Frost-free" or "freeze proof", etc.:

enter image description here

They come in different lengths, and the actual valve is all the way to the right of this picture where the copper meets the brass. This causes the entire valve to drain so no water is exposed to outside temperatures. The actual water pipes will be well inside the wall of the home and will generally not be exposed to freezing temperatures.

Here is another diagram to help explain from this answer:

enter image description here

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thank you, just to clarify, I still need to make sure that there is no water pressure in the pipe, so I have to have another valve on the inside of the house, then just leave this valve open and let it dry out? If so, then there is no magic ;-), I wanted some solution I don't have to care about – AndyZ Feb 26 at 13:56
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No, turning the knob on this valve closes the water off on the inside. It drains itself, and there is nothing else to do. One valve and done. – JPhi1618 Feb 26 at 13:58
    
Oh..OOOOH....now I see, ok, that sounds a lot better :) Yes, thank you, I got it. – AndyZ Feb 26 at 14:00
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Disconnect the hose before winter comes! I've had to replace my share of these and when I do, I add a valve anyway; these are not fool-prof. IME these sometimes only last a few years and if the vacuum breaker gets stuck, you'll be glad you put a valve in so you can shut it off and deal with it next summer. – Mazura Feb 27 at 8:49
    
You need to remove the hose so water can gravity-drain out of the pipe area (shown blue in the above diagram). If it stays in there, it will freeze and crack the sillcock. – Harper Feb 27 at 16:02

Freezing water can generate pressures scientists have only recently been able to experimentally verify. For more practical examples:

So exactly how much force is the ice capable of exerting? Well, people have been trying to work this out for a long time. In 1784 and 1785, one Major Edward Williams took advantage of the weather in Quebec and repeatedly tried and failed to find a method of containing ice. Williams at first tried to seal water inside of artillery shells, the cast iron plugs of which were launched 475 feet at an astonishing 20 feet per second when the pressure become too great. Unperturbed, Williams then took to anchoring the plugs in place using hooks, only for the shells to split in two.

In another experiment, an attempt was made to fill cannons made of one inch thick cast iron with water only for them too to split when it was frozen. Academics in Florence later tried to fill a ball made of one inch thick brass with water only for that too to crack when it was frozen. They later worked out that the force required to do so clocked in at around 27,720 pounds.

For a more exact answer, you need to once again go back the the water phase diagram, which shows that ice will turn into Ice II when the pressure reaches 300 Mega Pascals, which is exactly, 43,511.31 pounds of force per square inch. In other words, that's the amount of pressure a container would need to be able to survive to stop water turning into regular ice, instead causing it to turn into Ice II.

(source)

The answer to a freeze resistant plumbing system is actually the opposite: make the pipes thin and ductile enough that they expand with the pipe. New, well manufacturered copper can often freeze a few times before splitting.

The problem with this is that each time the copper expands, it becomes more brittle. Metal workers know that as you stretch, compress, or otherwise work copper and most other metals they develop internal stresses which cause them to be more brittle. The process of annealing can reduce or eliminate these stresses, restoring the metal's ductility.

So a copper pipe can often withstand a few freeze/thaw cycles. The joints are much less forgiving, though, and a lot of frozen pipe failures occur at or near joints where stresses cannot as easily distribute.

Thus the short answer to your question is that there is no practical size of pipe that will withstand frozen water.

There are a multitude of methods to handle this, though, the most common is the freezeproof faucet or hydrant.

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They're mis-reading the phase diagram. If you want a non-expanding form of ice, you only need to resist ~200MPa to get ice III. A back-of-the-envelope calculations says that a high-strength steel pipe with a wall thickness equal to 10% of its radius can do the job for a few winters, although the repeat freeze-thaw cycles will weaken it over time. – Mark Feb 26 at 22:05
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@Mark that's exactly what I expected and what I wondered about, so why not make the wall thickness equal to 100% of the inner radius, this would last maybe for a human lifetime? – AndyZ Feb 27 at 7:15
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@AndyZ, cost. McMaster will sell you high-pressure pipe rated at 40MPa for $50 per foot (compare ordinary copper pipe at $3 per foot). How much do you think a pipe five times stronger will cost? – Mark Feb 27 at 9:27
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@Mark don't look at the cost from that perspective, look from the other side, a copper pipe costs 3$ per foot, so make it ten times thicker and it MUST cost only 30USD ;-) – AndyZ Feb 27 at 19:11
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@AndyZ make it ten times thicker and it costs $300 - amount of material required in a pipe is proportional to (square of outer diameter) - (square of inner diameter). – Jules Feb 29 at 9:23

Fist gotcha is that nothing is actually freeze proof only freeze resistant (you were right to word your question that way) up to a certain point. Heating units are about as 'proof' as you can get, until of course they fail for whatever reason, and of course they have their own other drawbacks.

That said, assuming you want or need the bib to be located closer to the garden, what you may need is a Yard Hydrant. These will drain the water in the pipe down below the freezing line in the ground. You'll have to run a pipe to below the frost line, which varies on depth based on several factors such as temp and type of soil. Talk to local builders or city officials to find out what the frost line in your area is.

Yard Hydrant-1

Yard Hydrant-3

(The actual hydrants have much longer standpipes.)

These hydrants are great but they are expensive starting around $120 USD and up. Most installation instructions forget about telling you to put some kind of stone or block under the elbow fitting at the end of the pipe in order to support it better. You should also put some drain rock below and around it and I recommend some landscape fabric surrounding the drain rock.

For more information on what and where the 'Frost Line' is: nsidc.org

I wish I could post more links but my reputation isn't high enough. ... a little help here ;)

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thank you, yes Ed Beal already linked to one of those in his answer, but the picture you added is better than a link :) – AndyZ Feb 27 at 7:21
    
Oh, I missed that one. I actually have two of these on my property and they work great! – JaredW82 Feb 27 at 7:32
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"up to a cretin point" Damn you, autocorrect! – David Richerby Feb 27 at 17:07
    
Missed that too :) – JaredW82 Feb 27 at 17:09

The freeze proof bibs above work on the wall of a house. If you want the faucet further from the house this hydrant style works great. The supply line is buried below the freeze level and the base of the unit is bedded in rock when you turn it off the water drains into the rock. We have 3 of these for our horses and they have never frozen. I plan on replacing our other 3 standard bibs this summer as they always freeze and break the valve.

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Thank you, no, I was thinking about a solution on the wall of the house. But this hydrant seems to be made of gold, at least the price suggests that ;-) – AndyZ Feb 26 at 14:03
    
They are worth it. For a wall unit @Jphil1618 gets +. – Ed Beal Feb 26 at 14:08
    
Found a wall unit for 40USD, I must admit the prices for the wall units are also very high. – AndyZ Feb 26 at 14:16
    
I've seen these used extensively on ranch-type properties where water outlets are needed on a fence line where they would have no protection from the elements. They are expensive on that particular link, but can be purchased cheaper at a local farm supply store. – JPhi1618 Feb 26 at 14:30
    
Yeah, the online prices for these things are insane. Sillcocks (the wall units) go for $13-20 locally at the building supply here. Much as I like to believe in American exceptionalism, other countries have also heard of winter. I would certainly not pay to import a US style fixture if your local building supply will have one that fits local hoses, gaskets and handles are readily available, and have metric hexes and threads. – Harper Feb 27 at 16:00

Ironically enough, the most resistant metal water pipe is the original - lead! It's ductile enough that when the pipe contents expand during freezing, the pipe stretches outwards without breaking. Of course there is a limit to how much it can manage this before the metal gets fatigued, the walls get thinner, and things start to leak, but it's probably the most resilient option.

The downside of lead is pretty obvious though - poisoning! So I wouldn't advise using it. :) Still, if you're asking about plumbing, it's worth remembering that the word "plumbing" comes from "plumbum" which is the Latin word for lead, and this is just one of the reasons why it was used.

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Well, yeah, lead is something to kill somebody, not to water you garden – AndyZ Feb 26 at 18:13
    
@AndyZ It took 2000 years to get something better! :) Lead oxide is chemically pretty stable (assuming your water is not highly acidic) and limescale lined the inside of pipes, so lead plumbing actually did not put toxic levels of lead in piped water. Historically, lead poisoning mostly came from the workplace, not from water. We have better and safer alternatives now though, so we use them. – Graham Feb 26 at 19:07
    
"better and safer alternatives", yes, I like those better :) – AndyZ Feb 27 at 7:17
    
Well nowadays you would just use a sufficiently ductile plastic. But then you have UV light to worry about. – Harper Feb 27 at 16:05
    
Good info. Especially the Latin word for lead. No wonder "plumbers" move so slow. They need to "get the lead out". 😉 – ArchonOSX Feb 27 at 17:49

No piping nor material is "freeze-proof" when full of water & in your application it shouldn't be tested. But, I agree with JPhi1618 get a Freeze Proof Sillcock to accomplish your project.Sillcock

Here are a few tips to using them optimally:

  1. Angle the handle end down slightly from the interior connection so it always drains completely after every use.

  2. Caulk the backside of the mounting plate after the exterior wall's hole has also been caulked or foam filled so air doesn't enter the house, have any possibility of getting to the interior's valve & inside heat can keep the majority of the valve above freezing.

  3. Partially Unscrew the Vacuum Breaker cap for anything left connected to the Sillcock in freezing weather, this protects the Sillcock & whatever's connected only if that item drains completely by gravity. Ideally, nothing should be connected in those conditions & they will be damaged or destroyed if they aren't separately & fully drained.

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thank you. But what about 10mm inside diameter of a tube and 30mm thick steel tube walls, would so little frozen water still break metal that thick? – AndyZ Feb 26 at 14:01
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Oh yeah absolutely, ice will break most everything, it may take a few freezes but the ice will win in the end. Plus, steel would not only rust out it would have a very bad electrolysis reaction to your copper if not connected correctly. – Iggy Feb 26 at 14:15
    
I cannot believe that 10mm of freezing water would create a force that high, at some point the ice starts to form different crystals ice II to ice XV, well, I don't need to produce ice XV, but there is some limit to what ice expansion force can do. The question is, is this force beyond of what is reasonable or not. A pipe with 1meter thick walls would be...let's say it would be heavy – AndyZ Feb 26 at 14:19
    
I know what you're saying & I can agree that ice has a limit...I wouldn't know the routine physics formula but I'm sure it exists somewhere. But, ice breaks mountains apart...we have to use explosives & jackhammers to match the strength of just rainwater ice. But, in your application there's no better 1-step solution than the freeze-proof Sillcock. Now, a 2-step solution is just a regular Sillcock outside & an interior shut-off that can be meters away from the Sillcock, that would beat the freeze-proof Sillcock ONLY IF performed right AND before freezing temps begin. – Iggy Feb 26 at 14:29
    
Well, the comment "ONLY IF performed right" says it all, forget to shut off water supply and to release the remaining water just once at the right time and you make your DIY store happy again. Yeah, seams like ice is a bitch if you can say so :) – AndyZ Feb 26 at 18:11

In frost resistant sillcocks the valve can still freeze depending on the inside/outside temperature, and depth of the valve. The traditional method of doing it is using a stop and waste valve further back, which requires closing/draining before freezing temperatures, and opening it after: http://diy.stackexchange.com/a/38208

In houses I've looked at the stop and waste valve had been as much as 3 meters in.

At -25°C outside consider doing both, especially if in the future the heat may be turned down. I couldn't find a formulas for depth; try to look in your neigbour's houses to see what they did and if it works for them.

I wouldn't blame you if you chose to just run a hose indoors during the summer to keep things simple! In your shoes this is the solution I'd prefer. I remember from childhood a garden hose attached to the kitchen facet, exiting through the window above the sink. The facet had threads so a garden hose could be attached, and there was a PVC fork on the facet so water could still be drawn in the sink.

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