The Brutal Truth About Hot Tub Energy Efficiency. Sometimes Less is More!
Updated: Aug 23, 2022
Hot tubs are a hot commodity with multiple brands, numerous dealers and hundreds of options making choosing the right hot tub a difficult task. At a glance, every hot tub looks the same from a shell and cabinet standpoint. It is difficult for consumers to understand the differences between how various hot tubs are made unless the cabinet panels are removed and an expert provides an unbiased explanation.
Before we dive into the various ways hot tubs are manufactured to conserve energy, we first need to understand how the plumbing and jets are installed. When a new home is built, the plumbing is roughed in and each plumbing line is capped before the installation of the fixture. After all of the plumbing rough ins are complete, the main line that feeds the home is fitted with a pressure tester and the entire system is pressurized to 100 psi or more. If there are any leaks, it is immediately apparent, and everything is remedied. Once complete, the system is pressure tested again, and when the system holds, a building inspector is called in for sign off. After the sign off, the application of insulation and drywall can commence. With this process in mind, it is infrequent for plumbing in the home to leak.
Hot tub plumbing, fittings and jets are installed during the hot tub manufacturing process and there is no reasonable way to cap the ends of the plumbing and jets to perform a pressure test. For this reason, the hot tubs are usually elevated on a holding fixture, filled with water, and run for a period of time. If any leaks are discovered, they are fixed, and the hot tub continues down the assembly line. The fundamental issue with this approach is that there may be weak joints and jet seals that begin to leak after the hot tub is transported and/or filled and run for some time. It happens to the best of manufacturers now and again.
With the dynamics of the plumbing now out of the way, we can directly address how different manufacturers insulate their hot tubs. It ranges from 100% foam-filled insulation between the cabinet, base and shell to almost nothing. Logically, 100% foam-filled insulation will provide maximum heat retention. But, if there is a leak as small as an O' ring, it is a nightmare to find and a hefty repair bill. So hefty that it's often not worth fixing, resulting in the hot tub being discarded or replaced. Please keep in mind that our plug and play hot tubs are 100% foam-filled so we are naturally not totally against this.
Like a home, the most heat loss occurs at the top, where heat rises. Modern building codes mandate R60 insulation in the roof and R24 in the walls of a home. With this said, a hot tub must have a high-quality hardcover that fits snugly and can be tied down securely on two sides of the cabinet. The hard cover should also include an insulating bumper seal down the center to prevent heat from escaping through the fold. With a high quality, proper fitting hardcover in place, it is like having a tight-sealing cap on a thermos bottle.
Now back to the 100% foam-filled hot tub vs the hot tub with almost no insulation. We believe that 100% foam-filled will retain the most heat but to what end? If there is a leak, it needs to be easily repaired, especially in the dead of winter. It doesn't happen often, but when it does, it is not something that is covered under an insurance policy because it is a manufacturer's defect. Manufacturer's defects are covered (or not) under manufacturer's guarantees, not insurance policies.
In our opinion, the best way to retain heat in a hot tub first and foremost is to have an excellent quality and tight-fitting hardcover. Next, the hot tub shell should be sprayed with high-density polyurethane foam insulation. Remember the white Styrofoam cups filled with hot chocolate at the skating rink or hockey game? It didn't take a lot of Styrofoam insulation to protect your hands from the burning hot chocolate. In the context of a hot tub, a reasonable layer of polyurethane insulation on the shell without covering the fittings and the jets makes sense. Then, each water pipe should be individually insulated. Should any of the pipes need repair, it's a simple matter of removing the insulation, making the repair and then reinstalling the insulation.
A hot tub should be placed on a flat level base, and in doing so, it is compressed to the ground with the weight of the water. To prevent the ground from pulling the heat out of the hot tub, an insulating barrier should be installed between the footwell of the hot tub shell, the ABS base and the ground. As the hot tub usually includes a cabinet to finish the four sides, it only makes sense that the inside perimeter of the cabinet be lined with insulation as an extra precaution to keep the cold air away from the equipment and hot tub shell.
Where hot tub pumps are installed within a tightly sealed cabinet, the ambient heat discharged from the pump(s) is contained to help keep the hot tub water warm. Buyers beware that this is an excellent way to improve energy efficiency during the colder months. During the warmer months and the summer heat, there must be a way to exhaust this heat. Otherwise the hot tub pump can heat the hot tub water beyond the set temperature, and/or the hot tub pump can prematurely wear out.
The professionals at Northern Hot Tubs can help you choose the right hot tub for your home and provide expert advice relating to hot tub energy efficiency. We will tell you straight up that installing 100% insulation between the cabinet, base, and shell will result in maximum heat retention. We do not build our hot tubs this way and we would not sell a hot tub built this way. If there is a plumbing leak or issue of any kind, it is an unreasonable and expensive repair procedure that we quite frankly would never want for our customers, hot tub dealers or our technical support team. Besides, the difference in hot tub energy efficiency is about 10% to 20% or $3 to $6 per month so why bother?!