Window air conditionre © D Friedman at Choose a Room Air Conditioner - BTU Chart

  • POST a QUESTION or READ FAQs about how to determine the necessary cooling capacity in BTUs for a room or building area cooled by a window air conditioner or a portable air conditioning unit

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Air conditioner BTU requirements: this article provides an air conditioner BTU chart shows how to choose a room air conditioner for window or through-wall mounting.

We provide room air conditioner or window air conditioner BTU sizing & choice charts.

We also show how to actually calculate how much BTU cooling capacity you need based on building area or square feet, and we warn about dehumidification problems if you buy an air conditioner that is too big for the space you are cooling.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Typical BTU Cooling Capacity Range for Types of Room Air Conditioners

Room air conditioners © D Friedman at

Portable, window, or through-wall air conditioners are typically described by their manufacturer as suited for:

Article Contents

Room Air Conditioner Sizing and Choosing Chart

The table below gives recommended air conditioning BTU's necessary to cool a single room. The data in the table assumes that the ceiling over the room is insulated and that the room is not over or is not itself a special heat-producing area such as a kitchen or boiler room.

Table 1: Base BTUs - Recommended Air Conditioner BTUs

Number of
Room Area
Room Area
One Room . 100 4,000 - 6,000
100 180 6,000 - 7,500
180 270 7,500 - 9,000
270 400 9,000 - 10,500
Several Rooms . 400 10,500 - 12,000
400 500 12,000 - 13,500
500 700 13,500 - 15,000
700 800 15,000 - 16,500
Large Areas  . 900 16,500 - 18,000
900 1000 18,000 - 19,500
1,000 1,100 19,500 - 21,000
1,000 1,100 19,500 - 21,000
1,100 1,200 12,000 - 22,500
1,200 1,500 22,500 - 24,000
1,500 1,700 24,000 - 25,500
1,700 1,900 25,500 - 27,000
1,900 2,200 27,000 - 28,500

Notes to the Table Above

Calculating BTU Requirements: instead of using the table above, and particularly where factors may make the table inadequate (examples are given just below) you may want to CALCULATE the BTU COOLING REQUIREMENT using the procedure given below in this article.

Ceiling height variations: BTU capacity tables for air conditioner selection typically assume typical 8 foot ceiling heights in residential spaces.

If your ceilings are significantly higher, say 14 feet or more, you may want to use the next larger room area size when selecting the BTUh capacity needed for your air conditioner, particularly if your building is located in a hot climate with higher heating loads.

Building heat gain rate variations: in locations of high heat gain or high solar gain such as a significant exposure to direct sunlight or many sun-facing windows, or for buildings with little insulation, you may need to select a higher-capacity air conditioner than given by the table.

How To Calculate the BTUs needed to cool a given space: follow this procedure:

Wall air conditionre © D Friedman at

  1. Calculate the total square feet to be cooled: Measure the size of the room (or rooms) to be cooled, to obtain total square feet.

    Multiply room length by width for each room and if there are multiple rooms, add the room areas together to get a single number.
  2. Read the Base BTUs needed from Table 1 below
  3. Add additional BTUs for these factors:
    • + 4,000 BTUs for each room below a ceiling or roof which is not insulated
    • + 4,000 BTUs for a home or residential kitchen included in the cooled area
    • + 1,500 BTUs for each window which receives significant daily sunshine
    • + 1,500 BTUs for a room over a kitchen or boiler room IF the kitchen or boiler room is actively producing heat during the cooling period
    • + 600 BTUs per person over two, if more than two occupants will be occupying the room during the cooling period
  4. Subtract BTUs from the total required if these factors are present:
    • - 1,000 BTUs if the room is on the shaded side of the building
  5. Calculate the final total BTUh needed from the above steps. This should place you in the right range of cooling capacity needed. Review the warning below about buying an oversized air conditioner.

How Much Cooling Capacity do we need Per Square Foot of Building Area? How Much Space can a Ton of Cooling Capacity Serve?

Sketch explaining how many square feet of building can be cooled with one ton of air conditioning power (C) Carson Dunlop Associates

Maybe 450 sq.ft. to 1000 sq.ft. of a typical home can be cooled per ton of cooling capacity: that is, one ton (or 12,000 btuh) of air conditioning can cool about 500 sq.ft. of space. Sketch courtesy of Carson Dunlop Associates.

But the real answer is, it depends. Some of the factors that affect the ability of an air conditioner to cool a space need to be considered besides just the number of square feet. These include at least the following questions about air conditioning load and cooling requirements:

Watch out: Don't Buy an Oversized or "Too Big" Air Conditioner

Sketch explaining that oversized air conditioners are a mistake (C) Carson Dunlop Associates

Watch out: Do not buy an air conditioner which is oversized (too many BTUh) for the area you need to cool. You may think that bigger is better, but not in the case of air conditioning.

To make a room comfortable the air conditioner needs to both cool the room air AND dehumidify the room air.

If the air conditioner is too large for the space to be cooled, the temperature will drop quickly and the A/C unit will shut off before the air has become adequately dry. The room will be either too cold or too humid for comfort. Sketch courtesy of Carson Dunlop Associates.

More detail about how to diagnose and cure an air conditioner that is not dehumidifying can be found at DEHUMIDIFICATION PROBLEMS

Other types of portable or individual-area air conditioners

Casement or narrow window air conditioner © D Friedman at

How to Determine BTUs or Tons of Cooling Capacity of an Air Conditioner from its Data Tags

A/C Size Mistakes: units too big or too small


(Apr 17, 2011) arnold said: very usefull information it helps alot to understands airconditioners performance

(May 3, 2011) nova said: Thanks. Very important information for choosing the right air conditioner. I appreciate that.

(July 22, 2011) Susana said: Finally I found a website with all the information I needed about AC!!! Thank you!


Continue reading at BTU SIZING FAQS for AIR CONDITIONERS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see DEHUMIDIFICATION PROBLEMS if your A/C or heat pump system is over-sized it may not dehumidfy adequately.

Or see this

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