What Size Pool Heater Should You Buy?
Don't Get Cheap! Pool Heater Size Helps With Efficiency.  

Figuring Out What The Right Size Pool Heater For Your Pool Is

The more BTUs a pool heater produces sooner it will heat the water in your swimming pool. It is necessary to calculate the number of BTUs necessary to heat your swimming pool according to the sizeof your pool . 

            Variables that come into play are:

  • surface area - The purpose of any heater is to heat the pool water at a faster rate than heat is being lost from the surface of the swimming pool. Once the perfect temperature has been reached a heater only needs to run enough to compensate for the heat that escapes from the surface of the water. Due to this fact it is a good idea to use a solar blanket in conjunction with a pool heater, or any piece of heating equipment for that matter, in order to maximize heater efficiency. With that said, the more surface area your pool contains through which heat can escape, the more BTUs a pool heater will need to produce to heat your pool water. Figuring out the surface area of your swimming pool is  easy and some sample calculations have been provided:

 

  • round pools: radius (1/2 diameter) x radius x 3.14
    • rectangular pools: length x width
    • oval pools: 1/2 length x 1/2 width x 3.14
    • rectangular pools w/ rounded ends: length x width x 0.8
    • kidney-shaped pools: length x width x 0.75
  • temperature rise - The temperature increase of your pool is  a calculation of your perfect  temperature minus theaverage ambient air temperature. The perfect temperature is  the final temperature you'd like your pool water to reach. The average ambient air temperature is the average daily temperature. It should be calculated on the basis of the coldest month you plan on using your pool. For instance if I lived in an area where the average temperature in May, the month I wished to start using my pool, was 65 degrees and my desired temperature was 80 degree water, my temperature rise would be 20 degrees (80 - 60).

 

With surface area and temperature rise calculated you can refer to the following chart to find just how many BTUs will be necessary for the desired heating effect on your swimming pool:

Temp Rise (degrees)

10 deg
15 deg
20 deg
25 deg
30 deg
 
 
Surface Area (sq. ft)
Required Heater Output in BTUs / hr:
 
200
21,000
31,500
42,000
52,500
63,000
300
31,500
47,300
73,000
78,800
94,500
400
42,000
63,000
84,000
105,000
126,000
 
 
 
 
 
 
500
52,500
78,800
105,000
131,000
157,000
600
63,000
94,500
126,000
157,000
189,000
700
73,500
110,000
147,000
184,000
220,000
 
 
 
 
 
 
800
84,000
126,000
168,000
210,000
252,000
900
94,500
142,000
189,000
236,000
284,000
1,000
105,000
157,000
210,000
263,000
315,000

* This chart is based upon a wind velocity of 3.5 mph. Multiply by a factor of 1.25 or 2.0 for wind speeds of 5 and 10 mph. 

After finding the right amount of BTUs / hr from the chart, compare pool heater models based upon the amount of BTUs  produced. The number can be found by multiplying the pool heater's input ( measured in BTUs ) by a pool heater's efficiency rating.

  • heater efficiency - Pool heater efficiency is represented by a percentage, according to the manufacturer, that represents the amount of energy a pool heater transfers to the water for each unit of energy (BTU) used to generate that heat. The US Department of Energy requires that all pool heaters have an efficiency rating of  78% or more.

 

An example of this would be a 400,000 BTU pool heater with an efficiency of 90%, this pool heater would therefore produce 360,000 BTU/hr.