Compare fuels for heating your pool

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When considering a boiler (furnace) for heating your pool, what fuel should you choose?

The first thing to consider is fuel storage, unless you have a piped gas supply you will need to have a tank for either heating oil or propane, (LPG)

The types of boiler that you could choose are limited to those that burn fossil fuels directly, as above, or electric, which are not really suitable for pool sized volumes of water, unless they are of very high wattage.

Of the standard gas and oil burning boilers you would need to compare both the fuel costs, and the efficience of the boiler to make a sound comparison.

Basic Facts:

* BTU = quantity of heat required to raise the temperature of 1 pound of water 1 degree F.
* 1 Therm of Natural Gas = 100,000 BTU's
* 1 Gallon of Propane = 91,000 BTU's
* 1 Gallon of fuel oil = 130,000 BTU's
* 1 Gallon of Water Weighs 8.00 pounds
* 1 cubic foot of water = 7.5 gallons

The first figure you need to work out is the area of your pool, If it is rectangular that is a simple length x width.


if it is circular use the formula pi times radius squared or half the width x half the width x 3.14

it is better to over estimate your pool size for these fuel cost calculations.

The second figure that you might want is the volume of the pool which is the area as worked out above multiplied by the average depth, so if the deep end is 6 feet and the shallow end is 3 feet, the average is 4.5 feet.

That make the area time the av. depth = xx cubic feet

example 500 (area) x 5 (av depth)= 2500 cubic feet

to convert that figure to gallons multiply by 7.5 = 18750 gallons

and to get pounds of water multiply by 8 = 150,000 pounds.

Next you need to look at boiler efficiency, and using british government figures for new condensing gas boilers a 91% efficiency can be expected the figure for LPG (propane) is better at about 93% while oil boilers are up to 97%. The figure that you use will depend on the make of boiler you decide on, and the official figures, but what it means is a 100,000 btu boiler with a 91% efficiency will produce 91,000 Btu.


If the water temperature is 68 f (20c) and you want to raise that to 92f (30c) a 24f rise in temperature you multiply 150,000 pounds of water by 24 degrees and get a requirement for 3,600,000 Btu's

a 100,000 btu natural gas boiler at 91% efficiency would burn for more than 39 hours and burn 3.6 therms of gas

a 100,000 btu propane boiler at 93% efficiency would burn for more than 38 hours and burn 40 gallons of propane

a 100,000 btu oil boiler at 97% efficiency would burn for more than 37 hours and burn 28 gallons of oil

Substitute your figures in to the calculations and use current prices to see what your costs would be.

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