Can “energy pig” hot tubs be greener?

Some people give Severin Borenstein a hard time when he takes a hot bath.

“The general criticism of owning a hot tub is that it’s a wasteful use of energy,” he says.

The main reason for such high energy consumption is the heating, which generally runs even on days when the hot tub is not in use, so that the water does not cool down.

Because Professor Borenstein researches energy economics at the Haas School of Business at the University of California, Berkeley, he was able to crunch the numbers for his household.

He and his wife use the hot tub regularly, about five times a week.

“To keep the hot tub hot every day, I would have to heat it for about 30 minutes a day on average to compensate for the heat loss,” he explains. The hot tub filters for about six hours a day and is emptied and refilled approximately three times a year.

The hot tub’s energy consumption amounts to approximately 18% of his household’s electricity consumption.

Professor Borenstein calculated that running a hot tub for a year produces slightly less greenhouse gas emissions than a one-way flight between Boston and London.

That’s significant, leading some to label hot tubs as “energy hogs,” along with heated sheds, swimming pools, and second refrigerators.

There are measures that can make pigs a little less greedy.

One factor is how the hot tub is powered.

Hot tubs usually come with their own electric heaters, so using a green energy source will reduce your carbon footprint.

These heaters can also be combined with solar water heating to reduce the need for electricity.

However, for those installing hot tubs in their homes, this can be another level of complexity.

For retail customers, “simplicity is key,” says Karl Rowntree, technical director of British hot tub manufacturer RotoSpa.

Holiday parks are more open to alternative heating systems, including solar and biomass boilers (which can run on wood pellets or even coffee waste) and heat pumps.

Mr Rowntree says an air source heat pump can cut energy costs by up to 75% and pay for itself within three years.

Other factors include how well the tub is insulated and covered to reduce heat loss; how big it is, which affects how much water needs to be heated; and temperature settings.

Mr Rowntree says energy efficiency features in the control system can also help. He uses a sleep timer on his own bathtub, which he puts to sleep between 11:00 and 07:00.

Even if it cools overnight, it’s still cheaper than leaving it on overnight, he explains.

Of course, there is the option of a wood-burning hot tub. Its environmental impact would depend in part on whether the wood came from a sustainable source, but burning wood always produces carbon dioxide.

Another important component for tourism operators is the behavior of guests. At AliKats, a collection of chalets in the French Alps, hot tubs are very popular.

However, the company, whose region has struggled with drought for the past few years, has identified its 1,500L hot tubs as an area where energy and water consumption should be reduced.

This led the company to implement a new hot tub policy where guests must pay more to use the hot tub in the summer or if their hot tub requires a mid-week water change.

“In the winter, most guests still want to check in to the hot tub, but in the summer, more and more guests are checking out,” says Al Judge, co-founder of AliKats.

As for mid-week water changes, the company believes this can be easily avoided with proper usage, such as showering before entering the hot tub.

Additionally, “a key thing we’ve done this year is insist on no drinking in the hot tub, and that’s allowed us to keep the water running a lot longer.”

Mr Judge explains: “When beer is spilled in a hot tub, the yeast reacts with the water (at 37.5 degrees) and it turns unpleasant very quickly. So by stopping drinking in the hot tub, it had a strong positive impact on the environment.”

The hot tub market has had a rollercoaster few years. Hot tub sales increased in 2020 and 2021, during the Covid-19 pandemic. In the UK, sales have fallen in 2022 and 2023 due to the high cost of living and high electricity prices.

Finally, “we’re starting to see an uptick now,” says Mr Rowntree.

He says RotoSpa was selling about 600 a year before Covid, 2,500 during the pandemic and about 1,000 now.

Much of the incremental increase relates to the popularity of hot tubs in vacation rentals. UK holiday property owners who are part of the Weekend Candy and ToWander UK networks report that a hot tub can increase bookings by 10-20%.

However, the cost of maintaining hot tubs can be significant. Last year at Yorkshire’s Baxby Manor, owner Barney Smith installed three air source heat pump hot tubs as well as solar panels and battery storage.

“Despite this, it still costs me around £100 between each switch to fully clean, refill and heat each hot tub,” reports Mr Smith.

Despite the maintenance and energy demands, many tourism entrepreneurs believe that hot tubs are now indispensable.

“I’d say they’re starting to be expected as standard,” says Yasmin Wilkes, owner of Loose Reins in Dorset, where hot tubs were added in 2022 and 2023.

In California, Professor Borenstein says a narrow focus on energy use may be missing the “bigger picture” of hot tub use.

“There are many things we do that have an impact on the environment,” he reflects.