Colorado · typical $200–$600
Frozen drain & sewer lines
Most people think of frozen supply pipes, but drains freeze too: lines that run through unheated crawlspaces, garages and exterior walls, condensate lines from high-efficiency furnaces, and shallow sewer sections during long cold snaps. A frozen drain looks exactly like a clog, but clearing it takes heat, not a cable.
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Sounds like this?
- A drain stopped working overnight during subzero weather
- Furnace shut down with a full condensate drain or ice at the outlet
- Drains in an addition or over a crawlspace freezing first
- Water backing up in the lowest fixtures after a long cold snap
- Ice visible where a drain pipe exits the house
Where drains freeze in Colorado homes
- Kitchen and laundry lines in exterior walls, especially on the north side
- Drains under floors over vented crawlspaces in older homes
- Lines in attached garages or bonus rooms above them
- High-efficiency furnace condensate lines that exit the house; when they freeze, the furnace shuts itself off
- Shallow sewer sections after weeks of hard cold, more common in mountain towns
What to do and not do
- 01
Stop sending water down it
Water poured into a frozen drain just adds to the ice and can back up into the house.
- 02
Warm the room, gently
Open cabinet doors and raise the thermostat. A space heater in the area (never left unattended) can help.
- 03
Never use an open flame
Torches on pipes start house fires every winter. Plastic drain pipe can also melt.
- 04
Call if it doesn't clear
Plumbers use steamers and hot-water jetters that thaw from inside the pipe without damaging it.
Preventing it next winter
Insulate drain lines in crawlspaces and exterior walls, seal crawlspace vents for winter, and route furnace condensate lines so they can't freeze at the outlet (a plumber or HVAC tech can add a heat cable or change the exit point). During a deep cold snap, running a little warm water through vulnerable drains a few times a day helps. More in preventing frozen drain lines.
Common questions
Can a drain line freeze?+
Yes, especially lines in exterior walls, crawlspaces and garages, and furnace condensate lines that exit the house.
How do plumbers thaw a frozen drain?+
Usually with a steamer or a hot-water jetter fed into the line, which melts the ice from inside without damaging the pipe.
Will a frozen drain pipe burst?+
Drain pipes aren't pressurized, so they burst less often than supply lines, but ice can still crack older pipe and cause backups.
Why did my furnace stop when it got cold?+
A frozen condensate drain is a common cause with high-efficiency furnaces. The safety switch shuts the furnace off when the drain can't empty.