What Size Window AC Unit Do I Need? (Performance VS Cost)

We all know window air conditioners can provide a comfortable and cooling environment, particularly on a hot day. However, not all models are created equal; some stand out in performance, while others focus on economic value. This post will tackle the most common question when buying a window AC: What size window AC unit do I need? We will teach you how to evaluate your needs, measure room sizes, functions, and the cooling capacity of a unit. Never end up with an over-powerful or underpowered AC from this point onwards.


Choosing The Best Window Air Conditioner

The bigger the room size, the bigger and heavier the window AC is required. To determine the proper size of a window unit, we will first need to calculate the room size that needs cooling. Measure the width, length, and multiply both to get the square footage. You can get the cubic feet by multiplying the square footage by the ceiling height.
Next, match your room size to the window air conditioner’s BTU rating. British thermal unit (BTU) is an international unit of measurement that shows the amount of heat an AC can remove from your home hourly. The higher the BTU ratings, the greater the cooling capacity. You can refer to the table below for the complete window air conditioner sizing guide.

Window AC Sizing Guide

Room Sizes For Cooling (sq. ft.)Capacity Needed ( BTU)
100 to 1505,000 to 6,000
150 to 2506,000 to 7,000
250 to 3007,000 to 8,000
300 to 3508,000 to 9,000
350 to 4009,000 to 10,000
400 to 45010,000 to 11,000
450 to 55011,000, to 13,000
550 to 70013,000 to 18,000

Other factors you will need to consider with regard to window air conditioner sizes:

  • The more, the merrier. Add 600 BTUs for every occupancy in the room.
  • Minus 10% of the BTU if the room is heavily shaded or faces the other side of the sun.
  • As 25 to 30% of the home’s thermal transference is transferred through the window, opt for higher BTU for a room with more than one window.
  • Newer homes are well-insulated over older homes, built before the 1970s. You will enjoy better cool air circulation and retention.
  • If you intend to cool the air in more than 1 room, consider installing a central air conditioning that is better suited for the job.

Finding The Right Size Window Air Conditioner

To summarize, it is vital to choose a proper size window air conditioner for your room, no matter how long the unit is running. An underpowered, undersized window AC will not cool the room completely, no matter how long it runs. An overpowered, oversized window unit is noisier, consumes more energy, freeze up, and is incapable of removing adequate moisture, leaving dampness in the air. If you are in the market for one, we suggest identifying the window AC based on the three categories below:

  • Small rooms (100 to 250 sq. ft.) – Look for a window air conditioner with 5,000 to 6,500 BTU ratings. Ideal for bedroom, guest room, home office, foyer, storeroom.
  • Midsized rooms (250 to 350 sq. ft.) – Look for a window air conditioner with 5,000 to 6,500 BTU ratings. Suitable for a tiny studio, meeting area, playroom, and medium-sized bedroom.
  • Large rooms (350 to 550 sq. ft.) – Step up for a window air conditioner with 9,800 to 12,500 BTU ratings. Best used in an open floor area like the dining room, kitchen, basement, garage, and master bedroom.

How Do Window Air Conditioners Work?

Window AC is a cheaper, easy-to-install alternative to a central air conditioning system that cools a single room. It uses refrigeration technology to reduce indoor temperature and humidity levels. Cold air will be recirculated while hot air will be dispersed outside. Depending on the model, most came with multiple preset cooling modes to help you maintain the coolness in a room. The air conditioner will turn on when the room temperature rises and turn off when it reaches the desired room temperature. Some model even comes with an additional heating mode that will come in handy during the winter season.

What Features To Look For In A Window AC

Once you have determined the right size window air conditioner to buy, the next step is to look into the AC unit's functionality. Below are some stand out features that you should consider:

  • Programmable timer - Set a specific time to switch on or off the air conditioner to conserve energy.
  • Remote control - Make adjustments to the air conditioner in the comfort of your sofa or bed.
  • WiFi-enabled/ Smart feature - Advanced version of remote control. Allows you to control and monitor the AC via smartphone, even if you are away from the house.
  • Digital display - Pairs well with the electronic controls that allow you to set a specific temperature or timer, which is not possible with a conventional physical knob button.
  • Ionizer - Generates millions of negative ions to remove airborne impurities like dust, mold, and pollen. Ionization technology is safe for home use, but you will have to do house cleaning to completely get rid of the impurities that adhere to a surface area.
  • Pre-filter - Traps dust and other large particles to prevent them from getting inside the evaporator/ condenser coils. Most filters are washable; you can reuse them repeatedly. Some models are better designed that allows easy filter removal for cleaning.

How To Install A Window AC

Window air conditioners come with a bundled window kit that can fit most standard-size windows (non-casement). Measure the dimension of the window frame and check if the kit matches the size. Next, install the air conditioner to the window and ensure it is securely placed to prevent any injury risk. As window air conditioners are heavy, get someone to assist you with the lifting. Contact a licensed HVAC specialist if you encounter any issues with the installation.

,strong>Pro tips: Make sure there is a dedicated power outlet under five feet, as most window unit cords are about 6 feet long. It will not work with an extension cord due to safety reasons. Most window AC uses standard 120V, 15-amp outlets. For models that use a higher 230V, 20-amp outlets, you will need to plug it into a new circuit with a 12 gauge wire. Avoid using a step-up or step-down transformer.

Window AC Maintenance And Cooling Tips

Choosing the right size window air conditioner is the first step of good ownership. You will need to perform regular maintenance to ensure the unit is working in tip-top condition. Here are a few ways to ensure optimal cooling efficiency:

  • Clean the air filter when it is dirty or according to the suggested interval time by the manufacturer. Use a brush attachment and gently vacuum out the trapped dust particles. Use lukewarm water and mild soap for stubborn particles that are hard to remove. Leave the filter completely air dry before reinstalling it.
  • Make sure there is smooth airflow circulation by clearing out any obstruction. Leave 2-4 feet of gaps between the window AC. Wipe away any dust buildup, particularly in the ventilation section. When possible, store the window unit or cover it during seasonal changes.
  • Weatherstrip can improve window insulation to prevent hot air from entering and cold air from escaping. Do it on all the windows.
  • Choose a more shaded window e.g. facing the north side, to boost the window AC cooling efficiency. Install a blind to block out sunlight from shining inside the room.
  • Out with the old, in with the new. Newer window AC with the Energy Star label has a higher standard Energy-efficiency ratio (EER) of 10 or above. It cools better and is more efficient to run.

Max Fernandez

A loving father and a dedicated reviewer for airfuji.com with more than 1000 air purifiers under his belt. Max Fernandez is also one of the million patients currently suffering from asthma. Feel free to nudge him if you have any questions.