AC Drainage and Condensate Line Guide

Every air conditioner produces water as it removes humidity from the air. Proper drainage prevents water damage, mold growth, and system shutdowns. This guide covers drainage for all AC types.

Why AC Units Produce Water

When warm, humid air passes over the cold evaporator coil, moisture condenses — just like water droplets on a cold glass. A typical AC removes 1-5 gallons of water per day depending on humidity levels. This water needs somewhere to go.

Drainage by AC Type

Window AC

Water collects in the bottom pan and drains outside through a small hole in the rear. The unit must tilt slightly backward (1/2 inch) so water flows out, not in. If you see water dripping inside, check the tilt angle first.

Central AC / Mini-Split

A PVC condensate drain line carries water from the evaporator coil to a floor drain, utility sink, or exterior. The line needs a P-trap (prevents sewer gas backup) and should slope at least 1/4 inch per foot. Many systems include a secondary drain pan with a float switch that shuts down the system if the primary drain clogs.

Portable AC

Auto-evaporative models recycle condensation through the exhaust hose. Others have an internal tank (empty when full) or a continuous drain port for a gravity hose.

Clearing a Clogged Drain Line

Turn off the AC system
Locate the drain line access point (usually a T-fitting near the indoor unit)
Pour 1 cup of white vinegar or diluted bleach into the line
Wait 30 minutes, then flush with water
If still clogged, use a wet/dry vacuum on the outdoor end of the line

Preventing Drain Problems

Flush the drain line with vinegar every 3 months
Keep the area around the drain terminus clear of debris
Install a drain line safety switch (auto-shutoff if clogged)
Insulate drain lines in unconditioned spaces to prevent sweating