Things to know about User Load
Not all states or municipalities use the same method in determining maximum bather load (BL).
Some illustrations are:
 Square foot of water surface area.
 Flow Rate (usually Flow Rate divided by 5)
 Gallons of water in the pool
 Different factors for areas of shallow, deep and
diving portions of the pool as well as the deck
Always operate in compliance with your
local or state code requirements.

The commonly accepted bather load calculation for spas is:
 10 sq.ft. for every user or BL = A divided by 10

Example:

You have a spa with a diameter of 11 feet.
What is the bather load?
The formula is BL = A divided by 10
But what is A?
Diameter = 11 feet
Therefore r = ½ of 11, or 5.5 feet
A = 3.14 x r x r
A = 3.14 x 5.5 ft x 5.5 ft
A = 3.14 x 30.25 ft^{2}
A = 95 sq.ft.
BL = A divided by 10
BL = 95 sq.ft. divided by 10 = 9 bathers
(always round in the direction of safety, in this case, down)

Filter Area is very much related to the manufacturer's specification for the amount of water
flow through the filter in question. These specifications are governed by standards as
established by the National Sanitation Foundation International (NSFI). The CPO^{®}
student should review the next section covering Filter Media Rates before any further examples
are offered regarding filter sizing.
Download CPO^{®} Tutorial