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
Portable, window, or through-wall air conditioners are typically described by their manufacturer as suited for:
Single Room Air Conditioner Capacity - typically for rooms up to 20' x 20' or 400 sq.ft. in area. BTUs in this product range are typically from 6,000 BTUh to
Portable room air conditioners - 7,500 to 14,000 BTUH, portable, using one or in some cases two flexible ducts to move heat from the room, through cooling coil and the compressor, to outdoors
Multiple Room Air Conditioner Capacity - typically for a total area of up to 800 sq.ft. BTUs in this product range are typically from 10,000 BTUh to 16,000 BTUh.
Large Capacity Air Conditioner Capacity - typically for multiple rooms or very large rooms up to a total area from 900 sq. ft. to 2,000 sq.ft. BTUs in
this product range are typically from 16,000 to 28,000 BTUh.
Central Air Conditioning - typically to cool an entire floor or multiple floors in a home. Also see A/C TYPES, ENERGY SOURCES
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
4,000 - 6,000
6,000 - 7,500
7,500 - 9,000
9,000 - 10,500
10,500 - 12,000
12,000 - 13,500
13,500 - 15,000
15,000 - 16,500
16,500 - 18,000
18,000 - 19,500
19,500 - 21,000
19,500 - 21,000
12,000 - 22,500
22,500 - 24,000
24,000 - 25,500
25,500 - 27,000
27,000 - 28,500
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:
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.
Read the Base BTUs needed from Table 1 below
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
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
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?
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:
What are the sun and heat characteristics of the geographic area where the building is located (southern U.S. vs. northern U.S. or Canada, for example)?
How much direct sunlight is falling on the building?
Is it bright hot sun or only partly sunny?
What are the exterior colors of surfaces on which sunlight is falling?
How well the building is insulated?
How drafty is the building?
How many occupants are in the building?
What other heat sources (or cooling sources) are in the building?
How high are the interior ceilings?
How does air circulate within the occupied spaces?
What defects in the air conditioning system need to be overcome, such as duct system errors or damage, dirty filters, blocked cooling coils, etc. ?
Watch out: Don't Buy an Oversized or "Too Big" Air Conditioner
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
Heating & Cooling units - capable of both cooling or heating a room using electricity. Basically these units are small heat pumps
that are mounted in a building window or wall. Heating/Cooling units will give two different BTUh figures, one for cooling and one for heating.
These figures will differ, for example, producing 18,000 BTUh in cooling mode but only 12,000 BTUh in heating mode. The difference between
heating and cooling, and the amount of heat actually available will depend also on the outdoor temperatures when in heating mode (as with
any heat pump system, the unit cannot provide heat below certain temperatures.)"
Slider or Casement Window units - narrow tall cooling systems which are designed to fit into the narrow space provided by
casement or slider windows.
Through-wall air conditioners - air conditioning units which are designed to be installed into a metal sleeve which is then
itself installed in an opening cut into the building wall, leaving windows unobstructed, or perhaps for use in a room without
a suitable window in which an air conditioner could be placed. BTU output is typically a bit more than the smallest window
air conditioners but otherwise is similar in range.
Portable room air conditioners - units on wheels which are plugged into an outlet but can be moved room-to-room and do not require a window for their exhaust.
cooling units are of modest cooling ability, typically around 10,000 BTUh though some producers such as Sunpentown offer units up to 14,000 BTUh.
Thanks to various industry and air conditioner sales publications and consumer pamphlets including Sears Kenmore(R) air conditioning sales
Sunpentown International (SPT), 21415 Baker Parkway, City of Industry, CA 91789, 800-330-0388 / 909-468-5288, produces portable room air conditioners. Web search 12/31/2010. FAQ for portable room air conditioners: http://www.sunpentown.com/learnmore.html
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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