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Heating, cooling & air
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How powerful an air conditioner do you need?
 
aircondwks.jpg

This worksheet, adapted from a printed version published by the Association of Home Appliance Manufacturers for the continental United States, can help you estimate how much cooling capacity you need. You'll need a tape measure, scratch paper, and a pocket calculator.

The worksheet guides you through the measurements needed to calculate the size of the air conditioner, and then it automatically calculates the final answer for you. We suggest that you print out the worksheet first, fill it out, then enter the information online.

Make the measurements listed. For each dimension or area, round it to the nearest whole number before entering it in the appropriate box.

Note: This worksheet is to be used only for the area to be cooled by a single air conditioner. If the room is connected to another by a permanently open door or archway more than 5 feet wide, consider the two rooms as one area and make all the necessary measurements in both rooms.

 
1. Geographical location
 

Select the city nearest to your location with a similar climate (continental US only).
   
 
2. Walls
 
  Measure the length of all walls, in feet. Add up three separate lengths:
 
 

A.    

Outside walls not exposed to direct sunlight
(facing north and/or shaded by adjacent buildings)

B.    

Outside walls exposed to direct sunlight
(facing other directions and unshaded)

C.   

Interior walls
 
 
  Enter the lengths in the three boxes below, and select the appropriate wall frame type.  
 



Outside walls facing north, and/or shaded

Total wall length
  feet sq.

  
 

Outside walls facing other directions, unshaded

   feet sq.  
 

Interior walls

   feet sq.  
  Wall frame construction
  
 

 

  (Note: For wall frame construction there are two choices: uninsulated or masonry up to 8 inches thick, insulated or masonry more than 8 inches thick.)
  
3. Ceiling
  Determine the ceiling height, in feet. Enter that figure in the box.  
  (Note: For a sloped ceiling, determine the average height
between the highest and lowest points.)

Ceiling height
  feet sq.

  
  Determine the ceiling area (length x width), in square feet. Enter that figure in the box, and select the appropriate category for insulation above the ceiling.  
   

Ceiling area
  sq. feet

  
 
Insulation above ceiling
  
 

 

  (Note: For insulation above ceiling, the choices are: uninsulated, no space above; uninsulated, attic above; insulated, no space above; insulated, attic above; occupied space above.)  
4. Floor
 

If the floor is on ground or over a permanent basement, skip this step and move on to step 5. Otherwise, determine the floor area (length x width) in feet, enter it in the box. The floor area is usually the same as the ceiling area.

  
 

Floor area
  sq. feet

  
 
5. Doors and arches
 

If the room is connected to another by a permanently open door or archway more than 5 feet wide you should consider it as one room; skip this step and go on to step 6. Otherwise, enter the width of the door or archway into the box.

  
 

Total width
  feet sq.

  
6. Windows
 

Calculate the area (height x width) of each window. Take the measurements in inches, then divide by 144 to determine the square footage. Jot down the area of each window for use below. Add up the total window area for each wall, enter it in the appropriate box and select the shade and glass type that best describes the windows on each wall.

  
  (Note: For shades the choices are: none, inside, and awnings. For overhead eaves, use shade type "awnings." Shades are not applicable for North walls. For glass, the choices are: single, double, and block. For storm windows, use glass type "double.")
  
 

Wall orientation

Adjustment factors

    
   
 


Northeast

Shades
 

Glass
 

Window area
  sq. feet

  
   
 

East

       sq. feet  
   
 

Southeast

       sq. feet  
     
 

South

       sq. feet  
   
 

Southwest

       sq. feet  
   
 

West

       sq. feet  
   
 

Northwest

       sq. feet  
   
 

North

       sq. feet  
   
7. Heat from people
 

Enter the number of people who normally use the room
(use a minimum of 2).

  
 

People in room
  (min. 2)

  
8. Kitchen
 

If the room includes your kitchen appliances, check the checkbox below and
skip step 9.

  
 

Room includes kitchen

    
9. Heat from lights and appliances
 

If this area includes the kitchen, do not enter this number and check the checkbox in step 8 instead. Otherwise, add up the wattage of all lights and appliances in the room, not including the air conditioner itself, and enter the total here.

  
 

Total wattage of non-kitchen appliances

Total wattage
  (min.2)

  
 

 
10. Hours of operation
 

Select how you would typically use the air conditioner in the given area. 

  
 

For use at any time of day

    
 

For use at night only

    
 
 
The number calculated tells how much heat builds up in the room each hour. The air conditioner's cooling capacity (BTU per hour) should nearly match the resulting number. A difference of about 5 percent between the number calculated and the air conditioner capacity shouldn't be significant.

Air conditioner worksheet results

Estimated cooling capacity & range Estimated annual hours of use Utility Rate
1200 , +/- 100   BTU/hour 997   hours/year   cents/kWh

The sizing calculation is not an exact determination of your cooling needs. Further, your needs will vary as room use and outdoor conditions vary. Select a model whose cooling capacity is within plus or minus 5% of the calculated value, for best cooling performance. Air conditioners for a conventional 115-volt circuit are generally available between 5,000 and 12,000 BTU/hr.

Your cooling load requirement is well below the minimum air conditioner size (5000 BTU/hr) that we tested and rated. You may have difficulty finding a model with such a small cooling capacity. Although a 5000 BTU/hr model can more than handle your cooling needs, it may not dehumidify the room properly because it is oversized. Consider redoing the worksheet with a larger area to be cooled.
Your cooling load requirement is well above the maximum air conditioner size that we tested and rated.
  • Some window-mounted room air conditioners can provide as much as 15,000 BTU/hr of cooling. Additionally, there are through-the-wall models that can provide even greater cooling although they require a dedicated 230-volt circuit.
  • Consider two smaller air conditioners that add up to your cooling load requirement.
You can find your electric rate (e.g. 8.4 cents/kWh or $0.084 /kWh) on your utility bill. In some states, the total amount may have to be summed from separate unbundled costs--so there will be charges related to the cost of the energy and charges related to delivering the energy. Often, your bill also includes surcharges for things like rising fuel costs that the utility can pass on to you, the customer. You can add these amounts into your total cost of electricity as well. Alternatively, you can call your electric utility to obtain your current cost for each kilowatt-hour of electricity.

Estimated annual operating cost

EER Cost EER Cost EER Cost EER Cost
               
               
               
               
               
               
               
               
               
               
 


Cooling load Annual use Utility rate
BTU/hour hours/year