Why Do Air Conditioners Drain Water?

by Erik North on September 26, 2012

Post image for Why Do Air Conditioners Drain Water?


On a hot, humid day, air conditioners are awesome. They’re awesome most other days as well but on hot, humid days especially so. As an energy auditor, even on particularly sweltering days, it feels a wee hypocritical having an electricity hog AC cranking away. But it sure is nice.

Air Conditioners Help How?

Air conditioners blow cold air on a hot day…the aforementioned awesomeness of the AC. But that’s the obvious way that air conditioners make you feel more comfortable. A less obvious way is that they also condense moisture from the air, reducing humidity. Lower humidity generally means more comfortable. But the moisture needs to go somewhere, and in this case that water is pouring out the back of your air conditioner.

A Simple How Do They Work

A very brief rundown of how air conditioners work. In any refrigerator unit, a refrigerant is circulated through a series of tubes (not the internet) where there is an expansion/evaporator on the interior and a condenser on the exterior.

The expansion/evaporator transitions the refrigerant from liquid to gas, absorbing heat. The condenser moves it back to liquid, expelling the heat.

The Streaming Water Figures In How?

How the heck does this produce water? Warm, moist interior air circulates over the cooled, interior refrigerant coils. This cools the air and since we’ve all read the post on relative humidity (here it is…go ahead, I’ll wait), we know that as air cools, it is less capable of hold water vapor.

Now unless you live in Arizona or a similarly arid locale, warm air means humid air. The air conditioner is kicking along, cooling the warm interior air of your house and at the same time, it is wringing water vapor out of the air. The cold refrigerant coils provide a convenient condensation point for all that vapor to collect, pool and eventually drain…hopefully to the outside.

Like I alluded to earlier, this has an added comfort benefit beside just being less hot. The cold air is the obvious selling point. But those dude who say ‘it’s a dry heat’ have a point, even if you’d like to drop a rattlesnake in their laundry. Humidity plays a huge role in our personal comfort.

Perspiration is your body’s cooling system. When you sweat, you expel heat. If the air is already saturated with moisture, the sweat on your skin will evaporate more slowly (or not at all). When the humidity is lower, sweat evaporates more easily and your body cools more readily.

Air conditioning pulls humidity out of the air, helping your body cool in multiple ways. So the next time you see water pouring out of the back of your AC, it’s just part of how air conditioners work and it helps keep you comfortable.

Leave a Comment

Previous post:

Next post: