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UpkeepBurst Pipe

How do I protect pipes in an unheated crawl space?

Stop the cold air first: seal gaps and holes in the foundation and around pipe openings. Then fit snug foam or fiberglass sleeves on every exposed pipe with no gaps, add a thermostat-controlled, UL-listed heat cable only where a pipe still freezes, and in a hard freeze let a faucet fed by those pipes drip. Keep the house heated to at least 55 degrees.

Free to ask. Local shops send quotes, and you pay only when you book one.

By Kasra Taheri, Founder, LoclisUpdated

Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.

Step by step

Read when to stop and call a pro, further down this page, before you start.

  1. Step 1: Find every pipe down there

    Before cold weather, go into the crawl space with a light and gloves and trace every supply pipe, noting any near vents, the rim joist or an outside wall.[2]

  2. Step 2: Seal the air leaks

    Seal cracks and holes in the foundation and around pipe and cable openings near the pipes so cold wind cannot blow across them.[8] Do not seal the foundation vents shut as a quick fix, especially if a fuel-burning appliance down there draws combustion air from them.[7]

  3. Step 3: Measure the pipes

    Clean and measure each pipe and buy sleeves whose inside diameter matches the pipe's outside diameter for a snug fit.[3]

  4. Step 4: Sleeve the pipes with no gaps

    Fit insulation along the full length of every exposed pipe, including elbows and valves, and tape the seams so no bare pipe is left in cold air.[8] Leave any old wrap already on pipes or ducts alone; it may contain asbestos.[7]

  5. Step 5: Protect yourself from fiberglass

    Wear gloves, goggles and a dust mask if you use fiberglass wrap or batts.[3]

  6. Step 6: Add heat cable only where needed

    Where a pipe still freezes, use a plug-in heat cable labelled for that pipe size, with a built-in thermostat, installed exactly as its instructions say.[4][8] If the outlet within reach is not GFCI-protected, have an electrician look at it before you plug in.

  7. Step 7: Check heat cable every fall

    Unplug it, then check its whole length for cracked or charred insulation and bare wires, and replace it if you find any.[4]

  8. Step 8: Shut off and drain outdoor faucets

    Shut off and drain the pipes leading to your outside faucets so no water is left to freeze.[1][9]

  9. Step 9: Drip in a hard freeze

    On the coldest nights, let a faucet fed by crawl-space pipes drip, hot and cold, so pressure cannot build if ice forms.[8]

  10. Step 10: Keep the house warm

    Keep the thermostat at 55 degrees or higher, even when you travel, and consider a freeze alarm for an empty house.[1][2]

  11. Step 11: Label the main shut-off

    Find and label the main water shut-off valve, and make sure everyone in the house knows how to close it.[1]

The short answer

Keep cold air off the pipes, then wrap them. Wind chill can play a major role in accelerating ice blockage, and thus bursting, in water pipes,[8] so a pipe in a drafty crawl space is at more risk than one in still cold air. Seal the drafts, sleeve every exposed pipe with no gaps, add a thermostat-controlled heat cable only where a pipe still freezes, and on the worst nights let a faucet drip.

Crawl spaces are a common trouble spot. Virginia American Water's list of areas that might be prone to freezing, such as crawl spaces, unheated rooms, basements, garages, and exterior walls,[2] puts them first.

1. Find the pipes and the drafts

Go down before the first hard freeze, with a good light, gloves and old clothes. Trace every supply line from where it enters the house to each fixture above. Pay attention to pipes near foundation vents, along the rim joist, close to the access door, and wherever a pipe or cable passes through the foundation wall. On a cold, windy day you can often feel the drafts with the back of your hand.

2. Seal the air leaks

Loudoun Water's advice is short: "Seal all leaks in crawl spaces and basements."[1] Cracks and holes in outside walls and foundations near water pipes should be sealed with caulking to keep cold wind away from the pipes.[8] Larger gaps around pipe penetrations can take expanding foam. A loose access door is worth fixing before winter too.

Do not seal the foundation vents shut as a winter quick fix. A U.S. Department of Energy Building America guide on converting a vented crawl space into a closed one warns that simply sealing the vents could make the situation worse, increasing the levels of moisture and potentially creating a deadly situation if naturally ventilated types of combustion equipment are located in the crawlspace.[7] The guide singles out natural draft-vented appliances "that depend on combustion air from the open vents"[7] in the foundation. For a fuel-fired furnace or water heater down there, the guide calls working out its venting and combustion air sources a critical first step[7] before any change to the vents. Closing a crawl space properly is a project for a crawl space contractor, not a winter fix.

Close-up of a metal water pipe with a lengthwise split from freezing, circled and labelled Burst in a pipe
Photo: Tomwsulcer, CC BY-SA 3.0, via Wikimedia Commons

3. Insulate every exposed pipe

Loudoun Water's advice is plain: "Insulate pipes in any unheated or drafty areas."[1] Virginia American Water says the same: Where pipes are exposed to cold, wrap them with insulation or heat tape.[2]

Before you start, look at what is already on the pipes and ducts. Old crawlspaces might have asbestos-based insulation wraps on ductwork and plumbing pipes.[7] General movement and unintentional contact with asbestos-based products can stir the fibers,[7] so do not cut, pull off or sleeve over old wrap you did not put there. Have it checked first (see below).

Pipe insulation comes as tubular pipe sleeves, spiral insulation wrap, and fiberglass batts that can be taped around the pipes.[3] Foam sleeves are the easiest in a crawl space. Clean and measure the pipe first and match the pipe's outside diameter to the pipe sleeve's inside diameter to ensure a snug fit.[3]

Coverage matters more than brand. It is important not to leave gaps that expose the pipe to cold air.[8] Cut sleeves to fit around elbows and tees, cover valves, and tape every seam and joint. Where a pipe sits right next to a vent or the rim joist, thicker insulation helps; specialty sleeves come as much as 1 or 2 inches thick.[8]

If you use fiberglass: "Wear gloves, goggles, and a dust mask when working with fiberglass."[3]

4. Add heat cable only where it is needed

For a stretch that still freezes, a heat cable can help, with care. Fairfax County Fire and Rescue's caution: "There are some specially designed, UL approved heat tapes that can be used in unheated areas, but again, you need to be careful. If these methods are used, be sure to follow the directions exactly; a slight variation could cause a fire."[9] Look for the label, and check to make sure the product conforms to UL 2049.[8] Choose one with a thermostat: "Tapes and cables with a built-in thermostat will turn heat on when needed."[8] Tapes without a thermostat have to be plugged in each time heat is needed, and may be forgotten.[8]

Read the cable's own instructions before you buy, because they differ. Frost King's, for example, say its cable can be used on water-filled plastic or metal supply pipes but not on drain lines, fuel lines or hoses, that it must not be buried or come in contact with the ground, and that the entire installation should be wrapped with 1/2-inch fiberglass insulation.[6]

Think about the outlet before you buy. The CPSC recommends GFCIs in kitchens, bathrooms, and other areas where the risk of electric shock is higher.[5] In our view a damp crawl space deserves the same care: if the outlet within reach of the cord is not GFCI-protected, or there is none, do not run an indoor extension cord down there. Upgrading or adding an outlet is a job for a licensed electrician.

Heat cable is also a fire risk if it is installed carelessly. The Consumer Product Safety Commission's guidance:

  • know the diameter and length of the water or drain pipe to be protected, then buy tape labeled for that size;[4]
  • tape should not be lapped over itself around the pipe unless manufacturer's instructions specifically permit it;[4]
  • and: "Don't cover heat tape with insulation unless the manufacturer's instructions suggest it; if insulation is recommended, it must be non-flammable, such as fibrous glass."[4]

In 1989 the agency said tapes and cables were involved in some 3,300 residential fires each year,[4] and that heat tapes and pipe heating cables should be inspected each fall.[4] Unplug the heat tape or cable first, then check the entire length of the tape for signs of cracked or charred insulation as well as bare wires,[4] and replace any that is damaged. Homeowners uneasy about checking cables under the house should consider turning the job over to a licensed electrician.[4]

5. Shut off what you do not use

If a line in the crawl space feeds only an outdoor spigot or an unused fixture, take it out of play. Fairfax County Fire and Rescue's advice: "Shut off water to unheated areas of your home and to outdoor faucets. Don't forget to drain these pipes."[9] Loudoun Water's advice for outdoor faucets: "Shut off and drain the pipes leading to your outside faucets and/or hose bibs so no water is left to freeze, expand and cause a leak in these lines."[1]

6. On the coldest nights

Let a faucet fed by crawl-space pipes drip. It is not a sure thing: "Leaving a faucet on with a slow trickle may or may not keep the pipe from freezing; you can't count on this method."[9] What it does reliably is pressure relief: opening a faucet will provide relief from the excessive pressure that builds between the faucet and the ice blockage when freezing occurs.[8] Where both hot and cold lines serve a spigot, make sure each one contributes to the drip.[8]

Keep the house heated. Loudoun Water's advice is to keep your thermostat set no lower than 55F[1], home or away. For an empty house, a freeze alarm can call a user-selected phone number if the inside temperature drops below 45 degrees.[2]

Stop and call a pro if

  • A pipe in the crawl space freezes every winter despite insulation, or has already broken. Fairfax County Fire and Rescue says you may consider having the pipe or pipes rerouted through less vulnerable areas,[9] which is a plumber's job.
  • You find old insulation wrap on the pipes or ducts. Do not disturb it. Old crawlspaces might have asbestos-based insulation wraps on ductwork and plumbing pipes, and the DOE guide says a certified asbestos abatement firm will have to be contracted to inspect and determine the best treatment strategy[7] if it is found.
  • There is no outlet near the pipes for a heat cable, or the outlet is old, not weatherproof or not GFCI-protected. The CPSC warns that GFCIs can prevent electrocutions.[5] Adding or upgrading an outlet is electrical work for a licensed electrician.
  • A furnace, water heater or other fuel-burning appliance is in the crawl space. Do not seal its foundation vents shut, and have a licensed HVAC or plumbing pro check where it gets its combustion air before anyone changes how the space is vented.[7]
  • You find standing water, a wet floor, sewage or mold in the crawl space.
  • A pipe is already split, bulging or dripping. Close the main valve and call a plumber.
  • The crawl space is too tight to move in safely, or you find damaged wiring, animals or a gas line in the way.

Next steps

Read why pipes burst in winter for the reasons behind these steps, and how to keep pipes from freezing for the rest of the house. If one has already broken, see what to do when a pipe bursts. You can also browse crawl space and encapsulation services, find plumbers in Blacksburg, or read all plumbing repair answers.

If a crawl-space pipe keeps freezing or needs rerouting, describe the job once and licensed local plumbers quote it.

Common questions

Is pipe insulation enough on its own?
Often, if the crawl space is reasonably tight and the sleeves cover every inch of pipe. Insulation slows heat loss; it does not add heat, so a pipe in a strong draft can still freeze in a long cold snap. Seal the drafts first, and add heat cable only to the stretches that still freeze.
Can I put insulation over heat tape?
Only if the heat tape's instructions say so. The Consumer Product Safety Commission's advice is not to cover heat tape with insulation unless the manufacturer's instructions suggest it, and if insulation is recommended, it must be non-flammable, such as fibrous glass.
Should I close my crawl space vents in winter?
Not as a winter quick fix. A U.S. Department of Energy Building America guide warns that simply sealing the vents can raise moisture and can be deadly if a naturally vented furnace, water heater or other fuel-burning appliance in the crawl space draws its combustion air through them. Seal cracks and pipe openings instead, insulate the pipes, and treat closing the crawl space as a project for a crawl space contractor.
Does leaving a faucet dripping really help?
It helps with the part that bursts pipes. Fairfax County Fire and Rescue says a slow trickle may or may not keep a pipe from freezing, so do not rely on it alone, but an open faucet relieves the pressure that builds between the ice and the faucet, which is what splits the pipe.
What if there is no outlet near the pipes?
Do not run an indoor extension cord into a damp crawl space. Adding an outlet is electrical work for a licensed electrician; until then, rely on sealing, insulation and dripping faucets.

Sources

  1. [1] Frozen Pipes, Loudoun Water. Checked October 26, 2026.
  2. [2] Virginia American Water Urges Customers to Prepare for Cold Weather (December 3, 2025), Virginia American Water. Checked October 26, 2026.
  3. [3] Pipes in Exterior Walls, U.S. Department of Energy, Building Science Education. Checked October 26, 2026.
  4. [4] Inspect Heat Tapes, Cables As You Winterize Your Home (September 27, 1989), U.S. Consumer Product Safety Commission. Checked October 26, 2026.
  5. [5] Home Electrical Safety Checklist (Pub 513, July 2008), U.S. Consumer Product Safety Commission. Checked October 26, 2026.
  6. [6] Automatic Electric Heat Cable Kit instruction sheet, Frost King (Thermwell Products Co.). Checked October 27, 2026.
  7. [7] Guide to Closing and Conditioning Ventilated Crawlspaces (January 2013), U.S. Department of Energy, Building America Program. Checked October 26, 2026.
  8. [8] Freezing and Bursting Pipes: How pipes freeze and burst, and what to do, City of Paola, Kansas. Checked October 26, 2026.
  9. [9] Frozen Water Pipes, Fairfax County Fire and Rescue Department. Checked October 26, 2026.

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