Discount Pool Supplies and Spa Supplies

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.

At the bottom of the page we have provided a CALCULATOR which takes many factors into account and will perform these calculations for you. 


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.

Use this calculator to get a reasonably good approximation of what your pool heating or spa heating costs will be under varying circumstances. The more complete the form the better your results will be.

Volume of Pool or Spa	Gallons - required
Surface Area of Pool or Spa in Square Feet	Sq. Ft. - required
Average Wind Speed	MPH
Heater Efficiency	% - required
Desired Temperature Rise	degrees - required
Air Temperature	degrees
Water Temperature	degrees
Cost of Fuel per therm (from utility bill)	$ Required

Select the BTU rating of the heater:

55,000 BTU Heater
100,000 BTU Heater
125,000 BTU Heater
150,000 BTU Heater
175,000 BTU Heater
200,000 BTU Heater
250,000 BTU Heater
265,000 BTU Heater
300,000 BTU Heater
350,000 BTU Heater
400,000 BTU Heater