Hot Tubs 101 Part Two Construction

It has been my experience that customers have three basic things to consider when deciding on which hot tub to purchase. These are construction, how is it built. This greatly impacts how long the tub will last, the cost to run, and overall repair costs. The second is maintenance, how easy will my hot tub be to take care of. This includes chemical adjustments, water changes, and equipment care. The third is Enjoyment, Relaxation, and Therapy. If the first two don\’t line up, then the third and main reason for buying a hot tub has become a waste of money.

The Frame

The Frame is the main structure that holds the shell upright. There are three basic types of frames. Wood, Steel, and Plastic.

Wood has been used on hot tubs since the beginning, and it is the most common material used today. The two types of wood used are dimensional lumber and pressure treated. Out of the two types, pressure-treated is preferred as it resists rot and decay from the elements. Even though it is not directly exposed, pressure-treated can eventually fail over time. Some manufacturers will cut costs by using common lumber. The problem here is its life span. Common lumber when used on a hot tub and exposed to wet, or snowy conditions have a much shorter life than pressure-treated. If you want your tub to last more than 10 years, common lumber in most cases won’t get the job done. You would be surprised that even some big names like Jacuzzi use common lumber to build their tubs, just to save money.


Steel, there are a lot of opinions about this material for use in hot tubs. The basic fact is that steel frames will rust in the same wet and snowy conditions that common lumber will rot in. Given the choice, I would choose pressure-treated lumber over steel. Even though the frame is not exposed, it can still rust from humidity, puddles of water from rain or snow around the outside of the tub, and most of all condensation. When your tub is running it produces heat, which is good at helping to keep the water warm but awful for the steel frame. In this scenario, cold air seeps into the cabinet, which can cause condensation when coming into contact with the warm air. Companies like Sunrise and American Whirlpool use this type of frame, and they make a great claim about a lifetime warranty. However, like anything else, it’s all in the fine print. Have seen many rusted-out tubs that customers have asked us to dispose of, which are usually less than 10 years old.


Plastic frames are the latest development in hot tubs. Just like wood, there are good plastic frames and also bad plastic frames. The biggest advantage of plastic is its longevity. It will not rot or rust and will last the life of the tub. Companies like Bullfrog and some Hotspring products do a great job with their plastic fame. Both use techniques in the plastic studs to increase their strength. Some companies in the market don’t spend the extra money to do it right but use it as a gimmick instead to sell more hot tubs.

Hot Tub Shells

The shell of a hot tub is basically the vessel that holds the water. There are types. Acrylic is the most common type. Thermoplastic and vinyl liner.

Acrylic as mentioned is the most common and used by most hot tub manufacturers. However, there are some differences in how they are made. Most manufacturers use the fiberglass method. This method is after the shell is vacuumed formed, fiberglass is then rolled on the backside to give it strength. The downside is often the acrylic is stretched very thin and can lead to spots that may wear out, and leak. Also, as the tub gets older, the fiberglass can deaminate, meaning it can separate from the acrylic, which can lead to shell cracking. The second way to make a shell is to co-extruded it with similar material, like ABS plastic. This process is a little more expensive, however, the tub will last much longer with fewer problems.

Thermoplastic is essentially plastic. This is a great material for a hot tub as it lasts a long time, and is also less expensive than acrylic. It can be used to make just the shell or like a roto-molded tub the whole structure. The only real downside is its visual appeal. Compared to acrylic, it can look very basic, like a picnic cooler.

Vinyl is used two ways, one is as a liner inside a frame like an above-ground pool, and the other is as an inflatable. Both of these are generally used in plug-in tubs.


This is a controversial subject based on individual opinion. Insulation is simple as a blanket around the tub. It can be loose blown-in like in some older homes or sprayed-on foam. Let’s take a look and see who you think the winner is.

The blanket system. This can be a blanket of insulation or a roll of reflective foil, or both depending on the manufacturer. The insulation blanket can be made from different types of material, but essentially work the same. This type is problematic as it has nothing to hold up the plumbing. Plumbing support is very important, without it plumbing connections will fail. A blanket system is also not airtight. Image laying in bed with a nice warm blanket, not having it covering your feet. The other type of blanket is a reflective foil. This is not really an insulator, just a heat reflector to try and hold heat in, just reflecting the heat back into the hot tub. It does very little to keep the cold out.


Blown-in is used by several manufacturers and is advertised as being environmentally friendly. If the plumbing is supported, this can be a great alternative to the blanket system. When done properly, this insulation is fully blown into every area of the tub except the equipment compartment. The downside of many of these is that it can make a great nesting home for small critters and if your plumbing should leak it may require replacing the insulation. Depending on its type.

Foam is the most widely used. It has the benefit of keeping the heat in and, the cold, out. Holds the pluming in place to prevent joint separation, which will extend the life of the hot tub. Depending on the manufacturer, some will only use a thin layer of foam around the shell and claim that their tub is fully foamed, which technically it is. However, the R-Value would be very low and have little or no plumbing support. All the top manufacturers that use foam will encase everything from the shell to the frame. This will give you the best R-Value, and plumbing that will not move under the stress of water surging and running through it. The only downside is if you should have a leak it will take some time to repair to remove the old foam, and then replace it.

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