How does a frost-free hose faucet work?

A standard outdoor faucet shuts off at the spout, right at the wall. A valve manufacturer's guide describes the problem: even when you turn a standard faucet off, water stays trapped in the pipe between the valve and the exterior wall, and when that water freezes, it expands with enough force to crack the valve or the pipe.

The frost-free design fixes that. Per the same guide, the key difference is an extra-long stem that runs through the exterior wall and connects to a valve seat located in the warm, heated interior of the home. The maker of the guide sells these valves, so treat its marketing language with care, but the mechanism it describes is the standard design, and the University of Illinois Extension describes the same result: frost-proof spigots reduce the risk of freezing water creeping back into the house, where a burst line can do a lot of damage in a short time.

1. 1You turn the handle outside. The long stem turns with it.
2. 2The stem closes the valve deep inside the wall. The guide says the valve sits where it is protected from the cold, so the water supply is shut off in the warm zone.
3. 3The barrel drains. Any water left in the pipe between the interior valve seat and the outdoor spout runs out through the spout due to gravity.
4. 4The pipe stays dry through a freeze. Ice has no water to form from in the exposed section.

This is why the faucet must slope. The guide says a frost-proof spigot must be installed at a slight downward angle toward the outside, that this is critical for the frost-proof feature to work, and that it must never be angled upward. It puts the angle at roughly 5 to 10 degrees when it describes drilling the hole for installation. If the barrel tilts up or sits dead level, water stays in it, and you are back to the problem of a standard faucet.

A hose left on. Everything above depends on the barrel emptying through the spout. A hose, a splitter, a timer or a nozzle left on the spout seals the outlet, and the water cannot drain. The guide calls a hose left attached the single most common cause of failure: the water freezes and bursts the pipe despite the design. The University of Illinois Extension gives the same warning for any spigot, saying to remove and drain the hoses and store them in a sheltered spot.

Cold that reaches the valve. The Illinois Extension is direct on this point: even though these spigots are called frost-proof, do not assume yours will never freeze. It depends on how cold it gets and how well insulated the home is, including the wall cavities where the spigot's supply is installed. The valve seat is meant to be in warmth, but a poorly insulated wall or a long cold snap can chill it.

Phoenix Water Services' household plumbing tips still apply to a frost-free faucet: remove and drain the hoses, and keep garage doors closed if supply lines run through the garage. Our page on how to winterize a hose spigot in Arizona gives the full sequence, and whether pipes can freeze in Phoenix explains how much cold you need before it matters.

Many frost-free faucets also protect the water supply. The guide describes a frost-proof anti-siphon sillcock as a model with a built-in backflow prevention device. It gives this example: if you leave a hose connected with its end in a bucket of water, a sudden pressure drop in the main line could pull that dirty water back into your plumbing, and the anti-siphon feature stops it. The Illinois Extension adds that new spigots usually come with an anti-siphon feature that keeps water from siphoning back from the hose into the home's water supply.

If your faucet does not have one, a screw-on vacuum breaker is the usual fix. Our page on what a hose bib vacuum breaker is explains when you need one and how it relates to backflow.

The Illinois Extension suggests that if you have a very old spigot, swapping it for a new frost-proof one can reduce the risk of a ruptured frozen pipe. A few checks help you decide:

• Does it leak or drip? Read why an outdoor faucet leaks first. A worn washer is a small repair. A frost-split stem is a replacement.
• Is it on a cold wall? An exposed north-facing wall is the harshest spot. Our page on pipes freezing in Phoenix covers the at-risk locations.
• Is it a standard faucet with no interior valve? Then a frost-free model, or an added interior shutoff, gives the most improvement.
• Where do you live? In Flagstaff and other high-country areas, where winters bring freezing temperatures, a frost-free faucet earns its keep. In milder areas, the same steps as always still work: hose off, line drained.

The guide also lists choosing the right length and type for your needs, and says that if you lack experience, install by hiring a professional plumber. The install involves drilling through the wall, soldering, threaded or push-fit connections and sealing the flange, and the slope has to be right. A wrong angle leaves the faucet defeating its own purpose.

### Three examples

These are made-up examples to show the reasoning, not real jobs.

Faucet drips a little after shutoff. A brief drip right after you close it is water leaving the barrel, which is normal for this design. A drip that goes on and on is a worn washer or seat.

Water shows up inside the wall when the hose is on. The faucet leaks only with the hose in use. The barrel may have split in an earlier freeze, and the crack only leaks under pressure. Shut the inside valve or the main shutoff and call a plumber.

New faucet, hose left on all winter. A homeowner replaces an old spigot with a frost-free one and leaves the hose attached out of habit. The barrel cannot drain. The faucet has done nothing wrong.

In short, a frost-free faucet is a simple idea done well: shut off the water where it is warm, and let the pipe behind the spout empty itself. It cannot do that with a hose on or a barrel tilted up. HQ Plumbing offers free estimates and upfront pricing, and can swap an old faucet for a frost-free one or add an interior shutoff.