It takes a lot of energy to heat a hot tub. For both environmental and financial reasons, the use of alternative energy sources — solar and wind — has exploded in the past decade. Little wonder that more and more hot tub owners, and potential owners, are inquiring about the feasibility of heating their water via the sun.
“I get asked about solar all the time,” says Donny Stiver, co-owner of Stiver’s Backyard & Leisure. A veteran of the hot tub business, Stiver and his wife, Melissa, relocated from Paso Robles, California, and opened their Marquis dealership in Colorado Springs in 2020. Over the past two years, he estimates he’s had 20 inquiries about solar systems specifically designed for hot tubs.
Stiver has tried for several years, without success, to find a suitable stand-alone photovoltaic (PV) system for powering hot tubs.
“I haven’t found one that is cost effective and can produce enough kilowatts and amperage to power a hot tub by itself, and is compact enough to be viable as an add-on to a hot tub,” he says. “I’m sure there’s a system out there. I just haven’t found it yet.”
I haven’t found [a PV system] that is cost effective and can produce enough kilowatts and amperage to power a hot tub by itself, and is compact enough to be viable as an add-on to a hot tub. I am sure there’s a system out there. I just haven’t found it yet.”Donny Stiver, Stiver’s Backyard & Leisure
Solar panels vary in size, but ones needed to power a hot tub can be more than 3 feet wide and 5 feet long. Some of the local solar companies Stiver talked to told him a system large enough to power a hot tub would require at least two panels.
“That’s a lot of square footage,” Stiver says. “Most of them aren’t the greatest looking things in the world and can mess up the aesthetics of the backyard. You can’t really dress up a solar array because you run the risk of casting shadows on the panels, which defeats the whole purpose. Not to mention that they are stupid expensive.”
Depending on the size and storage capacity, such a system can start at $7,500. Some solar industry companies and at least one pool supply company offer customers information on heating hot tub water with heat-exchange panels. These are fairly simple, low-tech systems that require a minimum of six hours of daily, unobstructed sunlight to work. They employ a large panel crisscrossed with small tubes set against a black background, which absorbs heat from the sun.
The heat exchange panels are often covered with a layer of plexiglass, Perspex or similar transparent thermoplastic, which further magnifies the heat. Cold water from the bottom of the tub passes through the tubes, where the sun’s rays heat it. Then, it’s piped into the top part of the hot tub. As the water cools, it drops to the bottom, then gets reheated as it passes through the system again.
There are attractive aspects of a system like this. The low-tech equipment is inexpensive to buy ($1,500 or less) and with no moving parts, they are easy to maintain.
While heat-exchange panels are used frequently with swimming pools, many spa retailers say they don’t work well with hot tubs. They don’t have the capacity to store electricity, so they only work when the sun is shining. Their simple technology doesn’t allow the user to control the temperature which, in the summer, can lead to scalding hot water coming into the hot tub.
Dan Jung is in a unique position to assess the viability of using solar power with hot tubs. He owns two companies in Winnipeg, Manitoba, in south-central Canada: Cedar Tubs, a hot tub manufacturing company, and Northern Lights Solar Solutions, a green energy company. Initially, the two companies originally started to pair solar thermal with hot tubs.
“Solar thermal never really panned out in the hot tub world,” Jung says. “To be honest, it really wasn’t a great fit. The solar thermal could get very hot, much hotter than the hot tub needs, and it could get very cold, when the hot tub needs more heat. Controlling the heat and the expense of it were the big issues.”
What Jung recommends for anyone wanting to offset the energy needs of their hot tub with solar is to install a PV system to the roof of the house, which can then supply power to any electrical appliance in the home, including the hot tub. An array of panels, regardless of the number needed, won’t clutter up the backyard, and a PV system allows the user to control the temperature of the water in the hot tub. The system also has the capacity to store excess electricity, which can be used later when the sun is not shining.
Jung recommends using an air source heat pump, which moves the energy found in the air and transfers it directly to the hot tub. Manufactured specifically for hot tubs, it can be powered by the PV system.
“The air source heat pump pairs well with photovoltaic,” he says, adding that it can reduce the electrical consumption by 75% to 80% on a typical hot tub installation.
While heat pumps can deliver heat with outside temperatures as low as minus 20 degrees, Jung notes, they can also chill the water, which can be an advantage on hot summer days in many parts of North America.
Ultimately, Jung says, a whole-house PV system is the most feasible way to pair solar power with a hot tub. And for spa retailers, at least in his part of the world, “the heat pump is where the market is.”