What size air conditioner do I need?
How to work out the BTU capacity your room actually needs, and why guessing costs you money in both directions.
First, the reassuring part: water dripping from your indoor unit is not refrigerant. Refrigerant is a gas at room pressure and it does not pour out as liquid onto your floor. What you are seeing is condensate — ordinary water pulled out of the air — that has failed to find its drain.
Cooling air makes water. Warm humid air passes over a cold coil, moisture condenses on the fins exactly as it does on a cold glass, and that water collects in a tray under the coil and runs outside through a drain pipe. When any part of that path fails, the tray overflows into your room.
The four usual causes
1. A blocked drain line
The most common by far. The drain pipe is dark, permanently damp and slightly warm — ideal conditions for biological slime, which builds up over a season or two until the pipe closes. Water backs up in the tray and spills over the front edge into the room. Clearing and flushing the line usually solves it completely.
2. A drain line with the wrong fall
Condensate drains by gravity alone; there is no pump in a standard split system. The pipe needs continuous downward fall from the unit to the outside. If it was installed with a dip, or has sagged over the years, water pools in the low spot and eventually backs up. This is an installation fault, and it will keep recurring until the run is corrected.
3. Ice on the coil, melting
If the coil freezes — from a blocked filter, a fouled coil or low refrigerant — a block of ice forms on it. When the unit stops, that ice melts all at once, far faster than the tray can drain, and it overflows. If your leak comes in sudden bursts rather than a steady drip, and the unit also cools poorly, this is likely the cause. Fixing the drain will not solve it; the icing is the real fault.
4. The unit is not level
The indoor unit should sit level or with the faintest tilt towards the drain outlet. If it was mounted slightly off, or the bracket has shifted, the tray tips the wrong way and water leaves at the far end instead of the drain. Common on units installed in a hurry.
What to do right now
- Turn the unit off. Continuing to run it means more water.
- Put a towel or a container under the drip to protect the wall and floor.
- Check and clean the filters — if icing is the cause, this is often the underlying reason.
- Look at where the drain pipe exits outside. If nothing is dripping there while the unit runs, the line is blocked.
Do not leave it running and hope. Condensate running inside a wall causes damp, ruins plaster and paint, and can reach electrical fittings. It is a cheap repair now and an expensive one after a month.
Preventing it
An annual service before the cooling season clears the drain line and the tray before they block, which is why units on a maintenance schedule rarely produce this call at all. Washing the filters yourself every few weeks during heavy use prevents the icing route as well.
If the cause turns out to be fall on the drain line or a unit that was never mounted level, get it corrected properly rather than repeatedly cleared. Those two faults recur every single season until someone fixes the underlying installation.