Step 1: Find the surface area of your pool. For a rectangle, multiply the length X width. For an oval, multiply the length X width X 0.89.
Step 2. Find your zone from the map below.
Step 3: Decide on the length of season for pool usage from the chart below and determine the Seasonal Collector Multiplier required for your zone.
Seasonal Collector Multiplier  
Zone  May  Sept.  March  Oct.  Feb.  Nov.  Year Round 
Zone 1  0.60  0.67  0.75  0.85 
Zone 2  0.67  0.75  0.85   
Zone 3  0.60  0.75     
Zone 4 & 5  0.67  0.85     
Zone 6  0.75  0.85     
Zone 7  0.85       
Step 4: Determine your basic Solar Collector Surface Area requirement. Multiply the surface area of your pool by the Seasonal Collector Multiplier from the chart above.
EXAMPLE: If your pool is a 16 X 32, located in southern New Jersey (Zone 5) and you wish to use it from May through September, the basic solar collector area required is 16 X 32 X 0.67 = 343 sq ft.
Step 5: Apply Correction Factors. If any of the below Factors apply, multiply the appropriate Correction Factor by your basic Solar Collector Surface Area from Step 4.
Pool / Collector Factors  Correction Factor 

a  If you use a solar cover:  0.85 
b  If pool is occasionally shaded between 9am and 4pm:  1.20 
c  If pool is screenedin or enclosed indoors:  1.25 
d  If pool is exposed to prevailing winds of more than 10 mph:  1.33 
e  If climate is dry and the relative humidity is less than 30%:  1.25 
f  If the collector faces in a direction other than within 30 degrees of due south:  1.05 
45 degrees East or West from due South:  1.10  
Due East:  1.25  
Due West:  1.15  
g  If collector angle is more or is less than 25  35 degrees from horizontal:  
if 15 or 45 degrees elevation:  1.10  
if horizontal or 60 degrees elevation:  1.25 
EXAMPLE: Assume the same pool in the example above from Step 4. If a pool blanket is used, the pool experiences occasional shading from a tree and the collector is to be installed on a roof facing 45 degrees west from due south:
Your total collector area required is:
343 sq ft. X 0.85 (pool blanket) X 1.2 (occasional shading) X 1.05 (45 degrees west from due south) = 367 sq ft. This translates into (9) 4' X 10' panels.
Note: As mentioned above, this calculation sheet was provided by the manufacturer, Solar Industries. I am currently using these panels on an 18' X 40' pool in New Mexico. Going thru the above calculations, I needed 512 sq ft of panels. I am using only 144 sq ft of panels due to space limitations. With less than 1/4 of the required panel area, I have gained about a month at the begriming and a month at the end of the season, using our pool from late April to the begriming of October. This pool is 10' deep and has 35,000 gallons. The typical solar gain out of the return jets was 1  1.5 degrees warmer than the pool. On average, running the pump about 8 hrs each day will turn over the water in the pool at least once. For me, this is a gain of about 710 degrees a week due to the solar panels only. I am very satisfied with the performance of the solar panels  even though I have much less the recommended panel area. I do however live in an area where the sun shines most of the time. The point is, I am glad that I did not use the recommended number of panels as it would have been overkill for my application  and maybe for yours too. As a suggestion, you might consider starting out with something less than that required by this calculation sheet. Then, if you are not satisfied, you can always add more panels.
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