How long will it take to heat my pool?
This is a question many
people want to know, it is both simple and complex as there are variables to
consider. The simple answer is to plug
and play with this basic formula:
Gallons of water (GW) multiplied
by the weight per gallon (8.33lbs) multiplied by the degrees desired divided
by the BTU output of the heater.
For example, a 20,000 gallon
pool heated 20 degrees with a heater output of 336,000 BTUs would look like
20,000 x 8.33 = 166,600 lbs of
166,600 x 20 = 3,332,000
BTUs needed to heat the water 20 degrees
3,332,000 ÷ 366,000 = 9.91
The variables include factors
like ambient air and water temperature, wind speed, hours of sun, if it is
direct or in the shade, surface area exposed to the elements and where you are
located. Needless to say, if you are
located at the north pole and its zero degrees outside, the pool is 40 degrees in
the middle of winter and there is a 10 mile an hour wind it’s going to take a
lot longer to heat your swimming pool than it would if you are at the equator in the middle of summer.
What about the cost?
This is another question
frequently asked and again there are variables to plug and play. The constant in the equation is the therms
per hour. There are 100,000 BTUs per
hour for every one therm. Most gas companies use therms as a common measurement
of gas used. So, a 400,000 BTU heater will use four therms per
hour of operation. The equation would be
the number of therms multiplied by the
cost of your gas. If your gas costs you
$1.20 per therm and we used the heating time from above at 9.91 hours we would get
4 x $1.20 = $4.80
$4.80 x 9.91 hours = $47.57 is what it would cost you to heat the water initially
maintenance cost would be less as you are maintaining that heated water and the
variables listed above can play an enormous factor in keeping your pool warm.
But, But... I use propane and
not natural gas!
Ok, so the equation is
altered a bit because propane is calculated into cubic feet instead of
therms. One cubic foot of propane is
equivalent to 92000 BTUs.
A 400,000 BTU heater will use
4.34 gallons of propane per hour.
400,000 ÷ 92,000 = 4.34
Lets say the propane costs you $3.00
per gallon, so 4.34 x $3.00 = $13.02 per
$13.02 x 9.91 hours = $129.00 is what it would cost you to heat using propane
As mentioned, the variables
can play a big factor in the equations. Many of these examples are based on a 70 degree day with full sun and a
wind speed of 3.5 mph. Kick up the wind
speed to 11 mph and the energy use goes up 25%. Your location, time of year, elevation
above sea level, use of a solar pool cover, surface area exposed to the
elements, the depth of the pool and whether it is an above ground or inground
pool are all considerations. The type of gas used, the price per BTU and the age of
your heater add to the complexities.
So, how fast and how much
does it cost to heat your pool? What a
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