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Previously in this series on the evolution of hot tubs, I mentioned an early downside of ownership: high heating costs. Forty years ago, many people stopped using their tub when cold weather arrived. For me, that’s when I want to use it the most. Snow gently falling. Jack Frost nipping at my nose. It makes me feel like breaking out in a Christmas carol. But I digress. Early hot tub owners often found the cost of running a hot tub exceeded the value received in return. Why was this the case?

What’s out of sight shouldn’t be out of mind.

That’s how I ended part three of this series and it’s a direct lead-in to the root cause of high energy costs. In the old days, many tubs had a footwell that rested directly on the deck or concrete patio. During manufacturing, the acrylic shell would be drawn by a vacuum system. A rigid sheet of heated acrylic was suspended over the mold. The vacuum was turned on and the acrylic was sucked onto the mold. Early vacuums weren’t good at forming the shell with even thickness throughout. Some were drawn so thin in spots such as tight corners that the acrylic discolored and was almost transparent. To solve the problem and provide structural support, shells were coated with fiberglass or a spray-on rigidizing material. The cheapest got by doing the least. Then, to ‘insulate’ the shell, a thin layer of foam was sprayed on the undercoating.

The root problem was in the footwell. By resting it directly on the deck/patio, there was a constant heat drain. Here’s a test you can do. Take a glass of hot water and set it on a cold countertop. Fill a second glass with equally hot water and set it on the same counter but with several layers of a folded towel under it. See how much faster the first glass of water cools. This was a big issue with early hot tubs and needed a quick solution.

Problem solved! (Kind of.)

Many manufacturers started adding thicker insulation to the shell. A few went as far as to completely foam the undercarriage. But the inherent problem was still the footwell resting directly on the support base. Sure, the extra insulation helped, but you still had the footwell heat drain. The solution was obvious. That footwell needed to be elevated. This was accomplished with the addition of boards placed underneath the footwell. The most common method was using two 2 x 4’s under the footwell area, equally distanced apart with insulation filling in the gaps between. Wood framing was not new to the undercarriage. It was frequently used to keep the tub from racking during transport, but now it served a new purpose. It allowed manufacturers to elevate the frame, add insulation underneath, and greatly reduce heat loss. It also had the beneficial effect of distributing weight more evenly and made deck building much easier. No longer was the footwell supporting upwards of half a ton or more per square foot. The rule of thumb became the need for the deck to support one-hundred-pounds per square foot. But that’s another story for another day.

Locking the heat in and making it rise.

This is where the true economy of hot tub heating comes from. There are differing theories about what is the best way to economize heating costs. Some manufacturers use full foam on the undercarriage. This certainly minimizes any heat loss via osmosis through the shell. Other manufacturers employ ‘Thermopane’. They put a good amount of foam on the shell, then put a separate layer of foam or an insulating sheet on the inside of the cabinet wall. This creates a heated air lock between the two components, similar in concept to a double-pane window. Waste heat from the pump motor circulates within the Thermopane chamber. Heat is contained and the cost of running the hot tub is minimized.

The final component in keeping heating costs low…and affordable.

Okay. You’ve contained the heat with great insulation both under and around the shell. Heat naturally rises. The secret is to take that heat that you have forced to rise and trap it in the water. Meet your hot tub cover. A good cover locks in most of the heat. A great cover locks in virtually all the heat. Unfortunately, a cover sometimes gets damaged. Small twigs or sticks dropping from trees or storms can punch little holes in the vinyl cover. Patch them if you see them. Once a cover gets waterlogged, it gets heavy and will never dry out. Furthermore, a waterlogged cover eventually sags, changing form. The result is massive heat loss.

Make sure anyone that uses the hot tub knows that the cover is not a seat. Many hot tub owners stop in to buy a new cover to replace one they broke by sitting on it. Lastly, if you have roofers, painters, or other home improvement workers at your home protect that cover! Roofers drop shingle rippers and painters drop paint scrapers. Vinyl siding installers drop siding pieces, hammers, cordless drills…you name it. To minimize the risk of cover damage, my recommendation is this. With the cover in place on top of the hot tub, spread out an old blanket on it. Then, place plywood sheeting on top of the blanket. Make sure there are no unprotected areas. Murphy’s Law states that if you leave even a small spot uncovered, that’s where the hammer will land.

It's time to put this series to bed.

It has been my intent to outline how hot tubs have changed for the good over the years. Solid state, sealed electronics have made it easier to adjust water temperature, regulate filtration, and simply stated, use! The advent of synthetic cabinetry has virtually eliminated tedious sanding and re-staining. Quality hot tubs now retain their furniture-like appearance far easier and longer than in years gone by. Properly engineered in today’s better hot tubs, jetting now provides true massage therapy with near total user control. Lastly, the cost of ownership is but a fraction of what it used to be. Better insulation under the footwell, on the interior, and on top of the hot tub lock in the heat and the savings.

I invite you to stop at Eastgate Pools & Spas. You’ll see how great a hot tub or spa can be. Maybe soon you will experience one at home.