How to Drain and Winterize Pipes: When It Matters on the Peninsula

To drain pipes for winter, shut off the main water valve, open every faucet from the top floor to the bottom, flush the toilets, and drain the water heater. That empties the lines so nothing is left to freeze and split a pipe. On the San Francisco Peninsula you rarely need to do this, because hard freezes are uncommon. It matters for vacant homes, cabins, second homes in colder places, and the occasional cold snap.

This guide explains when winterizing is worth the effort here, how to do it correctly, and what to do if a pipe has already frozen.

Do You Need to Winterize Pipes on the Peninsula?

For most occupied homes in Pacifica, San Francisco, Daly City, San Mateo and along the coast, the answer is no. The heat is on, the home is occupied, and the coastal climate keeps overnight temperatures mild. Plumbing runs inside heated walls, so full winterizing is overkill.

It is worth doing in these cases:

• A vacant house or an investment property between tenants. No one is there to notice a leak or a cold spell.
• A second home or cabin in a cold area. Tahoe homes owned by Peninsula residents are a common example. These are the places where a hard freeze can actually split pipes.
• A long trip with the heat turned off. Draining the system removes the risk.
• A rare cold snap. Exposed pipes in a garage, crawlspace, or exterior wall are the first to go. Outdoor spigots and irrigation lines are too.

Frozen pipes are less of an issue here than in other parts of the country, but a burst pipe in a closed-up home can do more damage than one in an occupied home, because water runs for hours or days before anyone finds it.

How to Drain Pipes for Winter, Step by Step

These steps apply to a vacant house or a seasonal home with a standard tank water heater. If you are not comfortable with any step, call a licensed plumber.

1. Shut off the main water supply. Find the main shutoff valve and close it. Tell everyone in the house first.
2. Turn off the water heater. For an electric heater, switch off the breaker. For gas, turn the control to pilot or off. Do this before draining so the elements or burner do not run dry.
3. Open the faucets. Start at the highest faucet and open hot and cold. Then open the lowest faucet or hose bib. Gravity helps move water out of the system.
4. Flush the toilets. Flush each toilet, then hold the handle down to empty the tank. Sponge out what is left in the bowl and tank.
5. Drain the water heater. Attach a garden hose to the drain valve, run it to a floor drain or the yard, and open the valve. Open a hot faucet or the relief valve to let air in. Leave the drain valve open until you return.
6. Drain outdoor lines. Disconnect hoses, open outdoor spigots, and drain irrigation lines.
7. Protect the traps. Water left in sink, tub and floor drain traps can freeze. Use only antifreeze made for plumbing systems. Never use automotive antifreeze, which is toxic.
8. Leave faucets open so any remaining water has room to expand.

Washing machines, dishwashers, ice makers, and water filters hold water too. Check each appliance manual for winterizing steps. Blowing out the lines with an air compressor is a job for a plumber, because too much pressure can damage fittings.

How to Keep Pipes From Freezing in a Vacant House

If the house will be empty but you want to keep the water on, the goal is to keep the plumbing warm. A Salt Lake City utility guide recommends opening cabinet doors under sinks so household air can warm the pipes, setting the thermostat above 65 degrees if you will be away for several days, keeping attached garage doors closed, and letting the faucet farthest from where water enters the house drip slowly. Moving water is less likely to freeze. Sources disagree on dripping faucets, and some water agencies discourage it to save water, so check with your local utility.

Other steps that help:

• Insulate exposed pipes in garages, crawlspaces and attics with foam sleeves.
• Seal gaps where cold air gets in around pipes.
• Know where your main shutoff is, and have a neighbor or property manager who can use it.
• Consider a leak sensor or smart shutoff valve for an empty property.

Freezing Water Pipes: What Happens

Water expands as it freezes. The ice itself does not always split the pipe. Pressure builds between the ice blockage and a closed faucet, and the pipe fails where that pressure peaks. Often the split is invisible until the pipe thaws and water starts flowing. That is why a pipe that “survived” a freeze can become a leak a day later.

How to Unblock a Frozen Drain Pipe

If a faucet gives no water in cold weather, or a drain is backed up, a frozen pipe is possible. Try this:

1. Open the faucet so water can flow once the ice melts.
2. Apply gentle heat with a hair dryer, heating pad or warm towels. Start near the faucet and work back toward the blockage.
3. Never use an open flame, torch or propane heater on a pipe. It is a fire risk and can damage the pipe.
4. Look for leaks as the pipe thaws. If you see water or cannot find the frozen section, shut off the main and call a plumber.

A frozen drain line is a different problem from a frozen supply line. If a drain is slow in cool weather, it may also be a normal clog. Our drain cleaning service covers that.

When to Call a Plumber

• You cannot find or reach the frozen section.
• A pipe has already split or is leaking.
• You want the system blown out or the water heater drained and checked.
• You are reopening a home after a freeze or a long vacancy and want a plumbing inspection before you turn the water on.

When you turn the water back on, do it slowly with the faucets still open. Close them one at a time as water runs. Check under sinks, around the water heater, and at any exposed pipe for leaks. Refill the water heater fully before turning it back on.

Frequently Asked Questions

How do I winterize a house plumbing system?

Shut off the main, open all the faucets, flush the toilets, drain the water heater, and drain outdoor lines. Protect the traps with plumbing antifreeze.

Is it better to drain the pipes or keep the heat on?

If someone will be in the home, keep the heat on. For long absences in cold places, draining is the safer choice because it does not depend on power staying on.

Can pipes freeze on the San Francisco Peninsula?

It is rare, but exposed outdoor lines and pipes in uninsulated spaces can freeze during a cold snap.

Get Help From Works Plumbing

If you are closing up a house, reopening one after a cold spell, or dealing with a leak, call Works Plumbing and Rooter, Inc. We are a licensed California contractor (CSLB #982663), family owned, and have served the Peninsula since 2009. We are open 24/7 with same-day service. Call 650-899-3542 or contact us online. For maintenance help, see our plumbing maintenance page.