Calculating the electricity use of a hot tub looks very simple on paper but is much more complicated in reality. And the bottom line is, you truly cannot know how much a hot tub will cost to run until you have one installed and you use it for an entire year. This is because the energy usage of a hot tub is based on many factors, including but not limited to:
- How often and for how long you use the tub.
- How high you keep the water temperature.
- The quality of the tub's insulation and cover.
- Your climate.
- The size of the tub and its location.
- The tub's voltage: 120 or 240.
- The cost of your electricity service.
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Why Hot Tubs Cost More in Reality
Hot tub manufacturers boast that some units cost as little as a dollar a day to run, estimating that the average hot tub user spends only around $50 per month at most to enjoy their hot tub. However, many of these estimates are based only on the time you're actually using the tub, completely ignoring the energy used to keep the water hot 24/7 as well as running the circulation pump periodically around the clock.
Given all the real-world factors involved, the best way to get a realistic estimate of how much your hot tub will increase your electricity bill is to ask neighbors who have hot tubs. They live in the same climate and probably pay the same electricity rates that you do. That will get you much closer to an accurate estimate than anything you'll learn from a local spa dealer or even from the utility company.
Basic Hot Tub Electricity Calculation
This is the very limited version of the calculation you'll find from most sources. It's based on the wattage of the hot tub and how much you actively use it. Again, this ignores the significant energy usage of keeping the water hot at all times as well as the outdoor temperature and other factors.
The heater is the hardest-working part of a hot tub, with a 120-volt heater using about 1,500 watts, and a 240-volt unit using about 6,000 watts. The circulation pump with the jets running uses about 1,500 watts on any large tub, whether it's 120 or 240 volts. Putting it all together means your hot tub will draw about 3,000 or 7,500 watts of energy while you use it.
Many 120-volt hot tubs are not capable of heating while the jets are running full-blast. Tubs on 240-volt power can be more efficient than 120-volt models in some situations.
Electricity is billed based on kilowatt-hours, however, not just wattage. A kilowatt-hour is the equivalent of using 1,000 watts over a period of one hour. A 1,500-watt heater uses 1.5 kilowatt-hours (1.5 kWh) per hour.
To determine how many kilowatt-hours you will consume while actively using your hot tub, divide the tub's total wattage by 1,000. With a 120-volt tub heating and running the jets, you'll use 3 kWh of electricity (3,000/1,000). Next, look at your electric bill to see what you pay per kilowatt-hour and then multiply.
The average cost of a kilowatt-hour of electricity in America is currently estimated to be 14.47 cents, according to U.S. Energy Information Administration. Let's say you plan to spend an hour a day in your hot tub, or 30 hours a month. That 30 hours multiplied by 3 kWh equals 90 kWh for the month. This 90 kWh multiplied by 14.5 cents ($0.145) per kilowatt-hour works out to an expense of approximately $13.05 per month.
That's a pretty reasonable price, but it only counts the time you use the hot tub, which doesn't represent your total expenses. When you consider that you're keeping hundreds of gallons of water hot for the other 23 hours of the day when you're not using the tub, you can see why this basic calculation is showing only part of the picture.
Remember Total Run Times
Since hot tubs use the most energy when they're actively in use, the more you use the tub, the more you'll pay. But what about energy use when you're not actively hot-tubbing? You can lower the water temperature a bit to save money, but your heater always needs to run intermittently to maintain that temperature. Also, keeping the water cooler when you're not using the tub means that the heater has to work harder and longer to bring the water back up to the desired temperature before you use it again.
You can decrease heat loss in the water by purchasing a well-insulated hot tub. Look for at least 6 inches of insulation material. A high-quality cover will also help your tub hold the heat, as will floating thermal blankets on top of the water. If you can, adding some type of roof or structure around your hot tub can also help it hold heat more efficiently so your heater runs less.
Even if you do everything you can to help yourself, the weather may not cooperate. If you're keeping your hot tub water hot on an outdoor deck in the middle of winter, expect your hot tub heater to have to put in some work. How much will depend on the difference between the outside temperature and the temperature inside your hot tub.
Your circulation pump may also run when you're not in the hot tub. This is necessary to keep running the water through the filtration system to keep it clean, and it's required during heating. The best way to combat this is to look for a hot tub with an energy-efficient pump. It's usually best to let your circulation pump run around eight hours a day, so energy efficiency is crucial.
If you do the math again using the same 14.5 cents per kilowatt-hour electricity rate, you'll see that running a 1,500-watt pump for eight hours a day equates to $1.74 a day, or about $52 a month. This is just for running the pump and does not include the heater. In climates with cold winters, keeping the water hot 24/7 can use significantly more electricity.
Other Ways to Reduce Energy Usage
One way to reduce your hot tub's energy usage is to think small. Larger tubs take more water to fill, which is a factor, but they also require more power. The more water you're heating and circulating, the more energy your hot tub will consume. Unless you plan to increase your popularity in the neighborhood by sharing your hot tub often, a unit sized for two or three people will likely be adequate and will cost a lot less to run.
Take your hot tub usage into account as well. If you use your hot tub only once a week or less, it might be more efficient to keep the water temperature a few degrees lower when you're not using the tub. Just be sure to turn up the heat a little earlier before you use the tub because the heater will need more time to get the water up to a usable temperature.