HOW
TO APPROXIMATE THE COSTS
OF HEATING YOUR POOL OR SPA
There are
numerous factors that affect heating costs, such as wind,
heater efficiency, surface area, type of pool/spa
construction, ambient temperature, whether or not the pool
is covered, etc.. This is only intended to be used as a
general guideline and should not be considered absolute. If
carefully done, however, you should get a reasonably good idea
of what your heating costs will be.
First, we need to
define BTU, or British Thermal Unit.
This describes the amount of energy it takes to raise one
pound of water, one degree Fahrenheit.
Second, we need to determine the number of gallons of water
in the pool or spa. Assuming you have a 15,000 gallon pool,
for example, you will be heating 124,650 lbs of water,
since1 gallon of water weighs 8.31 lbs.. To heat this water
1 degree will then require 124,650 BTU's.
Third, we need to factor in a heater's efficiency rating.
Most heaters sold today run in the 80-83% efficiency range.
Basically, this means that you lose about 20% of the BTU
input as wasted energy. So, now you need 149,580 BTU's to
heat this water 1 degree, or approximately 150,000
BTU's.
Fourth, since we are billed in therms and not BTU's, we need
to translate this into therms. (one therm = 100,000 BTU's).
This pool, with today's average heater, would require 1.5
therms to raise the temperature 1 degree fahrenheit.
Fifth, we need to determine the cost of a therm. Gas costs
vary greatly from area to area, and often by season, so you
need to determine this from your gas bill. For the sake of
simplicity here, let's assume a cost of $0.75 per therm. 1.5
therms times 75 cents per therm = 112.5, say 113 cents, or
$1.13. So, to raise the temperature of this pool, say 10
degrees, would cost $11.30, assuming, for simplicity's sake,
that there was no heat loss.
A 250,000 BTU heater costs, from our example, $1.88 per hour
to operate, based on our per therm price of 75 cents. As you
can probably tell, this heater uses 2.5 therms per hour. A
300,000 BTU heater uses 3 therms per hour, and so on.
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