Stay warm, and may your drains flow freely.

When the wind chill drops below 20°F (-6°C), cold air seeps through foundation vents, missing insulation, or cracks in the siding. That cold air hits the cast iron or PVC pipe. Add a little bit of standing water left behind after your shower, and you have a recipe for a solid ice plug. Here is the gross truth that plumbers know but rarely advertise: Bathtub drains freeze faster than other drains because of soap scum and hair .

The thin layer of organic sludge that lines your drain acts like a sponge. It holds moisture against the pipe wall. When freezing starts, that sludge creates a rough surface for ice crystals to latch onto. Within a few hours of your morning shower, a partial blockage can turn into a full ice dam. A frozen tub drain isn't just an inconvenience—it can be a disaster. When you run water to try to melt the ice, the water has nowhere to go. It backs up into the tub.

Here is why your tub drain freezes, why it’s dangerous, and how to thaw it out before you end up with a costly repair. We tend to think of our plumbing as existing entirely inside the warm envelope of our home. But the bathtub drain is a trickster.