There are so many variables when trying to calculate how much it would cost to heat your spa.

In order to set your mind at ease, for this particular exercise, we will take a typical portable spa with the most basic functions to give us a reasonable outcome.

Depending on which country you live in, or what area of each country you may reside, the formula is still the same.

Every spa has a pump, a filter, and a heater of some sort. For this exercise we will assume that your heater is electric, and there are no extra auxiliary loads ie blower, pool light, ozone etc

The first part of this exercise is to total the amount of power (Kilowatts) that your spa is likely to use at any given time.

Pumps are rated in horsepower (hp), and 1hp = 746watts (0.75kw) 230 volts

Spa pumps will vary in type and size but it would be just a matter of checking the nameplate on your pump to confirm the hp size. Most spa pumps range from 1hp – 2.5hp depending on the manufacturer.

Electric heaters also vary in type, and size, but for our purpose we only want to know the actual heater size in kilowatts.

Most portable spas have a heater ranging from 1.5kw – 3kw

At this point, the only other variable required for our calculation is the cost of the power that you are charged by your power company.

Power company’s philosophy is to not only make a profit, but to spread the load equally amongst its local population. Although this point may be debateable, that is another topic all on its own and we wont have the room to discuss that here.

Power supplier’s charge on a "cost per unit used" basis and every homeowner should have that cost included in their power account. Each unit is based on 1 kilowatt per 1 hour. So, as an example of this calculation, if your account states that each unit costs 23 cents, that is basically saying that 1 kilowatt of load for 1 hour will cost you 23 cents.

To calculate our total load in kilowatts the combined power is:

Pump 1hp = 0.75kw (1.5hp = 1.12kw, 2hp = 1.5kw) 230 volts

Heater = 2.0kw

Total kw = 2.75kw

What is the point of all this useless information you might ask?

In 3 steps based on the information you have just established, you can calculate how much it would cost to heat your spa per hour, per day, and per month.

For the next step we need to apply a mathematical equation, and using the information above, will give us our end result.

The formula for calculating this cost is:

$ = cost per unit x total kilowatts

$ = 23 cents x 2.75kw

= 0.63 cents per hour

Now lets assume its going to take 12 hours to heat your spa up, this would cost 0.63 cents x 12 hours

= $7.56 as a One-off heat up time for the first day

If your spa needed 3 hours per day to maintain that temperature, it would cost

= $1.89 per day

Over a month (30 days)

=$62.37 per month (including first day start up)

Please note, that these calculations are based on New Zealand voltages (230volts), and New Zealand Power Providers. You would need to know your country’s voltage to apply to kilowatt loading calculation.

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