The short answer
Why Pipes Freeze with Heat On
Your heating system warms the air where the thermostat sits, usually a central room. But water lines run through places that never get that warm air: under floors, inside exterior walls, in garages, or in crawl spaces. If those areas are poorly insulated or have air leaks, the temperature around the pipes can drop below 32F even while your living room feels toasty.
Another common cause is a furnace that cycles on and off but doesn't push warm air into every corner. A blocked vent, a broken blower motor, or a dirty filter can reduce airflow to far reaches of your home. You might feel warm near the register, but the far side of a closet or a stairwell stays cold enough to freeze a pipe.
How to Find the Frozen Spot
Start by feeling along exposed pipes in unheated areas. Look for frost on the pipe surface or a section that feels much colder than the rest. Also check for bulges or cracks, which mean ice has expanded and may have split the pipe. If you see water dripping or a small leak, shut off your main water valve right away to limit damage.
Listen for reduced water flow. Turn on a faucet at the lowest point in your home. If the water trickles or stops completely, the freeze is likely between that faucet and the supply line. Work backward from the faucet, checking each accessible section of pipe. If you have a crawl space, be careful stepping on insulation or wiring while you look.
- Feel for cold spots on exposed pipes
- Look for frost, bulges, or cracks
- Check under sinks and in cabinets
- Inspect the attic and crawl space
- Turn on a faucet to test flow
- Shut off the main valve if you see a leak
Safe Ways to Thaw a Frozen Pipe
Never use an open flame, a blowtorch, or a propane heater to thaw a pipe. That can melt the pipe or start a fire. Instead, apply gentle heat with a hair dryer, a heat lamp, or a portable space heater set to low. Move the heat back and forth along the pipe, starting near the faucet and working toward the frozen section.
Wrap the pipe in towels and pour warm water over it, or use an electric heating tape designed for pipes. Keep the faucet open while you thaw so water can escape as ice melts. If you can't reach the frozen area or the pipe is behind a wall, you may need to call a plumber or a water damage pro to handle it safely.
When to Call a Water Damage Pro
If a pipe has already burst, you likely have water spreading through walls, floors, or ceilings. Shut off the water and electricity in the affected area if safe to do so. Then call local water damage pros to extract standing water and begin drying. The longer water sits, the more damage it does to drywall, wood, and insulation.
Water damage pros use moisture meters and drying equipment to remove hidden moisture. They can also help with structural drying and dehumidification to prevent mold and rot. If the freeze happened in a hard-to-reach spot, a leak detection service can locate the exact break without tearing open your walls unnecessarily.
How to Prevent Future Freezes
Insulate exposed pipes in unheated areas with foam pipe sleeves or fiberglass wrap. Seal gaps around pipes that enter your home from outside, using caulk or spray foam. Keep garage doors closed and open cabinet doors under sinks on cold nights to let warm air circulate. Let a faucet drip slowly during extreme cold to keep water moving.
Know where your main shutoff valve is and how to use it. If you leave for vacation, set your thermostat no lower than 55F, and consider draining your water system if you'll be gone for weeks. Keep your shutoff valve location written down so you can act fast in an emergency.
- Insulate pipes in the attic and crawl space
- Seal air leaks around pipe entries
- Keep garage doors closed in cold weather
- Open cabinet doors to warm the pipes
- Let a faucet drip during hard freezes
- Know where your main shutoff valve is
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Call Now (469) 698-4610Frequently asked questions
How long does it take for a pipe to freeze?
It depends on the temperature, pipe location, and insulation. A pipe in an unheated attic can freeze in a few hours when outdoor temps stay below 20F. But even a mild 25F night can freeze a pipe if cold air blows directly on it.
Can I use a space heater to thaw a pipe?
Yes, but safely. Place the heater at least a few feet from the pipe and never leave it unattended. Keep it away from flammable materials. Move it slowly along the pipe, and keep the faucet open so water can flow as ice melts.
What should I do if a pipe bursts?
Shut off the main water valve immediately. Then turn off electricity in the affected area if it's safe. Call the pros to extract water and dry the area. Take photos of the damage for your insurance claim, and check your policy for coverage details. Policies vary, and your insurer decides what is covered.