Frozen Pipes: Prevent and Thaw Safely

How do you prevent frozen pipes in a mountain home?

You prevent frozen pipes by keeping warm air around them: hold the heat at 55°F or higher, open sink cabinets on outside walls, and run a pencil-thin stream of cold water on the coldest nights. Colorado Springs Utilities, a Colorado municipal utility, gives all three steps and warns that turning the thermostat off "can lead to frozen or broken water pipes."

The steady trickle matters most on a faucet far from where water enters the house. Arlington County, Virginia, suggests opening the faucet farthest from the main valve to a small, steady trickle, and closing off crawl spaces, sealing drafty doors and insulating walls and attics so cold air never reaches the pipes.

Up here the season is long. NOAA's 1991–2020 normals for the Aspen 1SW station (about 8,175 feet) count roughly 210 days a year with a low at or below 32°F and about 14 nights at or below 0°F. Down-valley at Glenwood Springs #2 it is about 6 nights at or below zero. Either way, a frozen supply line is a question of when, not if, for a house left cold.

Freeze numbers for the valley

• 55°FLowest thermostat setting, even when awayColorado Springs Utilities
• 14Nights a year at or below 0°F, Aspen 1SW (1991–2020)NOAA NCEI
• 6Nights a year at or below 0°F, Glenwood Springs #2NOAA NCEI
• 32°FBelow this, Carrier requires a condensate freeze kitCarrier 59SC5A manual

Which pipes freeze first?

The pipes that freeze first are the ones closest to cold air: supply lines inside outside walls, under kitchen and bathroom sinks on exterior walls, and anything running through a crawl space, attic or unheated garage. Colorado Springs Utilities singles out cabinets "against an exterior wall," and Arlington County points to crawl spaces, drafty windows and doors, and thin wall and attic insulation.

Outside, the ground itself freezes deep. Garfield County's building code requirements sheet lists a frost depth of 36 inches up to 8,000 feet and 42 inches above 8,000 feet; that is a commercial code sheet, but it shows how far down the cold reaches. Hose bibs, sprinkler lines and any pipe near a vent or foundation crack are weak spots too.

How do you thaw frozen pipes safely?

Thaw a frozen pipe slowly with gentle heat: a hair dryer, a heating pad or warm towels, working from the faucet end back toward the frozen spot with the faucet open. Colorado Springs Utilities says to start "nearest to the faucet" so melted water can drip out, and not to use a hair dryer around standing water.

Never use a torch, kerosene heater or any open flame, and keep heat away from anything that can burn (Arlington County). Arlington also says not to thaw a water meter yourself.

If a pipe has already split, shut the water off at the main valve right away. Arlington suggests marking that valve with fluorescent paint or tape so you can find it in the dark. When the pipe is inside a wall you cannot reach, or the thaw does not bring water back, call a licensed plumber.

Is heat tape safe for frozen pipes?

Heat tape is safe only when it is the right product for that pipe and is used exactly as its maker says. In a 1989 safety release the CPSC, the federal product safety agency, told owners to unplug heat tape each fall and check its whole length for cracked or charred insulation and bare wires, replacing it if any turn up.

The same release says to buy tape labeled for the pipe's diameter and length, not to lap tape over itself unless the instructions allow it, and not to wrap it over thermal insulation. If insulation goes over the tape, the CPSC says it must be non-flammable, such as fiberglass, and only where the maker recommends it. Owners unsure about checking tape under a house can hand the job to a licensed electrician.

Outdoor heat tape also costs money up front in two jurisdictions: under the REMP exterior energy rules, Aspen charges $3.26 per watt and Pitkin County $3.39 per watt.

Can a furnace condensate line freeze?

Yes. A high-efficiency (condensing) furnace makes water as it burns gas, and that water drains through a trap and a plastic line that can freeze if it passes through a cold crawl space, garage or outside wall. Carrier's 59SC5A installation manual says that where the temperature may fall below 32°F a condensate freeze protection kit, a trap with a heat pad, is required, and it allows only self-regulating, shielded, waterproof heat tape rated 3 to 6 watts per foot on the rest of the drain line.

A frozen drain backs water up, and that alone can shut a furnace down. That is why a cold house with a no-heat problem is worth checking for ice at the drain. Where the furnace sits below the nearest floor drain, a condensate pump lifts the water out; the pump, its discharge line and any freeze kit are a technician's job to fit and route. PlumbingSupplyAndMore's condensate pumps (part of Upvalley Heat's ownership group) show what these parts look like. If you are unsure, stop and call a qualified technician.

What should a second-home owner set up?

A second home needs heat that stays on, water that can be shut off, and someone who checks the house after storms. Colorado Springs Utilities says to keep the thermostat at 55°F and turn off the indoor water supply at the valve when you leave; Arlington County adds that a home with a boiler or other wet heating system left vacant should be set up by a licensed plumber.

Snow is the other risk. After a big storm, both plastic pipes of a high-efficiency furnace need to be clear: makers set them a foot or more clear of the snow they expect, and a drift can shut the furnace down (see snow-blocked vents). Ask whoever checks the house to look at the vents and the thermostat reading on each visit.

A furnace or boiler that stops in a power cut leaves pipes exposed too; the winter power outage page covers that. For the wider picture of cold-weather risks, start from the cold snaps overview.

Lift-line questions

More on cold snaps

• Folder: Cold snaps in the valley: pipes, outages and lost heat
• Cold snaps: Safe checks when the furnace stops
• Cold snaps: Keeping warm when the power goes out
• Radiant and snowmelt: Boiler care and glycol