Guide · updated 2026-10-02
How to keep drain lines from freezing this winter
Colorado winters swing from mild afternoons to subzero nights, and arctic fronts can drop temperatures fast. Supply pipes get the attention, but drain lines in the wrong spot freeze too, and a frozen drain in January usually shows up as a backup at the worst time.
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The drains most likely to freeze
- Kitchen and laundry drains in exterior walls, particularly north-facing ones
- Drains in rooms over vented crawlspaces in older ranch homes
- Lines through attached garages or bonus rooms above them
- Furnace condensate lines that exit the house (a frozen one shuts the furnace down)
- Shallow sewer laterals during long cold spells, especially in mountain towns
Before winter
- 01
Insulate exposed drain pipe
Foam pipe insulation on drains in crawlspaces, garages and unheated basements is cheap and quick.
- 02
Close crawlspace vents
Many older homes have vents meant for summer airflow. Closing them for winter keeps the space well above outdoor temperature.
- 03
Check the furnace condensate exit
Make sure the line slopes properly and exits where snow and ice won't block it. A heat cable is a common fix for lines that freeze.
- 04
Know where your cleanout is
If a line does freeze or back up, the plumber will need it.
During a cold snap
- Open sink cabinets on exterior walls so house heat reaches the pipes.
- Run some warm water through vulnerable drains a few times a day.
- Keep the garage door closed if drains run through it.
- Don't set the thermostat very low at night or when traveling.
If a drain freezes anyway
Stop using that drain, warm the space gently and give it time. Never use a torch on any pipe. If it doesn't clear within a few hours, or water starts backing up elsewhere, a plumber can thaw it from inside with a steamer or hot-water jetter. See frozen drain and sewer lines.