What Is the Purpose of the Vent Open or Closed on a Window Air Conditioner?

Photo Courtesy: Getty Images / x Cavan Images

The vent on a window air conditioner is an opening in the unit where outdoor air can enter the room and where indoor air can be exhausted. With the vent set on “open,” outdoor air is allowed into the room. This increases the pressure in the room which forces out some of the indoor air. When the vent is set on “closed,” the window air conditioner simply circulates and recycles the air inside the room.

Why Vent?

Also called the “damper” switch, the vent in older windows and wall-mounted AC units look like a tiny black knobs in the air inlet grill from where cold air is being blown into the room. Pulling on the damper opens the vent, while pushing it in closes it. Newer models will just have a button in place of the damper, labeled as “exhaust.”

If you are using the AC to cool a room, it will seem counterintuitive to open the vent and let the cool air out. So why open the vent in the first place? There are several reasons why you may want to open the vent, and one of them is to replace stale, indoor air with air from the outside.

When the window air conditioner is set on “Fan Only,” you’ll want to blow in cooler outdoor air, rather than recycle indoor air. The temperature of recycled room air tends to become warmer due to the combined body heat of the occupants. Since window air conditioners pull moisture out of the air, opening the vent will also be a good idea if the cold conditioned air becomes too dry.

How a Window Air Conditioner Unit Works

As its name implies, these semi-portable cooling units are mounted on the window. Most models come with mounting brackets and insulation pads to make DIY installation easier for homeowners. Window air conditioners come with various cooling power for different cooling (or heating) requirements.


Window AC units work by pulling warm indoor air through evaporator (or cooling) coils on the front air intake grill. These coils contain a refrigerant, which the AC compressor cycles and keeps cold. The evaporator on the front intake grill cools the warm air by pulling both the heat and moisture from it.

The cooled air is blown back into the room, while the moisture becomes the condensate that drains out via the exterior part of the window air conditioner. The hot refrigerant cycles through the coils at the back of the AC unit where a blower cools it down. The compressor then pushes the refrigerant through a small coil opening, which further lowers its temperature as it returns to the coils on the front intake grill for the next air cooling cycle.

Will Opening the Vent Use More Power?

If the vent on a window air conditioner were opened from time to time, then it wouldn’t have much of an impact on utility bills. However, if the vent is left open for longer periods, the AC unit and its power-hungry component, the compressor, will need to work harder. It’s a good idea, therefore, to open the vents only when necessary, and for shorter periods to cut down on your electric bill.


What Window Air Conditioner Size Do You Need?

When it comes to AC units, bigger is not always better. Before purchasing a unit, take measurements of your window and the square footage of the room where it will be installed. Armed with this information, the experts at the hardware or appliance store will recommend the ideal type and size of AC for your room.


An AC’s cooling power is measured by BTUs or British Thermal Units. As a standard, a 7,000 to 8,000 BTU AC is usually recommended for rooms with a floor area of 250 sq. ft. Spaces measuring 300 to 425 sq. ft, on the other hand, need 10,000 to 12,000 BTUs of cooling power. Rooms larger than 425 sq. ft should have ACs with no less than 14,000 BTUs of cooling power.

Other Factors That Can Affect the Efficiency of Your Window AC

Apart from the floor area and window size, you’ll also have to inform the experts at the appliance store about several variables. These include where you plan to install the AC, the ceiling height of the room, the number of doors and windows, and the room’s usual number of occupants. This additional information will further help the experts determine the right size and model window air conditioner unit for you.