When it comes to reducing the running costs of a hot tub, nothing has a bigger impact than the hot tub’s insulation. Today, we will look at the most common hot tub insulation systems to see which one performs best. We will also show you a couple of ways that you can improve your hot tub’s insulation; regardless of the system it uses. Before we get to that though, let’s first look at how hot tub insulation actually works.

How Does Hot Tub Insulation Work?

Hot tub insulation works by trapping warm air in small pockets. Air is a great insulator as it resists changes in temperature. This slows the transfer of heat out of the hot tub as the colder outside temperatures now need to travel through hundreds or thousands of small air pockets, instead of simply radiating in through the cabinet. By slowing down potential changes in temperature, the insulation allows the radiant heat generated by the hot tub to be trapped inside the cabinet; keeping the water inside warmer and preventing any potential for freezing.

What Types Of Insulation Are Used In Hot Tubs?

There are three main types of insulation used in hot tubs; spray foam, fibre board and thermal shield insulation.

  • Spray Foam. A widely used hot tub insulation that is also commonly used to insulate homes. It is a special liquid that when sprayed on a surface will expand and trap air as it dries.
  • Fibre Board Insulation. Stiff boards made up of interwoven fibres. While fibre board insulation is cheaper and easier to replace than spray foam, it also leaves small gaps around each piece; reducing its overall effectiveness.
  • Thermal Shield Insulation. A thick “bubble wrap” style insulation that is commonly used in a variety of applications where high amounts of insulating value is needed in a relatively small space (like water heaters or astronaut’s space suits). This insulation has two sides, one that is reflective to reflect heat back into the system (to reduce the amount of heat transferred by the insulation), and the other which is black to absorb any ambient heat coming from outside the system.

What Are The Different Hot Tub Insulation Systems?

Now that we know what types of insulation are used in hot tubs, the question becomes how these different types of insulation are utilized to improve your hot tub’s energy efficiency. Although each hot tub manufacturer insulates their hot tubs in slightly different ways, most fall into one of the following 3 categories.

1) Full Foam Insulation

“Full foam” insulation is the most common way that hot tubs are insulated. In this system the foam (usually spray foam) is applied directly to the shell and plumbing of the hot tub; fully insulating the water and the majority of the plumbing. While this system is very effective at insulating the water, it does have a couple of potential drawbacks. These are:

If the foam gets wet it needs to be removed and replaced. Wet foam is completely useless as an insulator. Spray foam is also notorious for retaining water once it is absorbed. For this reason, even small leaks can lead to large repair bills as large areas of foam have to be removed and replaced.
Hot tub heaters and pumps generate a lot of waste heat. In a full foam system these components are left outside of the insulation. This means that all that waste heat is, well, wasted.

2) Perimeter Insulation

In an effort to solve the issues of full foam insulation, some hot tub manufacturers switched to a perimeter foam system. In this system, the insulation is installed on the inside of the hot tub’s cabinet. By insulating the cabinet of the hot tub, perimeter insulation systems allow the waste heat from the pumps and heater to be trapped and used to further heat the hot tub water. They also leave the plumbing exposed for easier repairs.

Perimeter foam isn’t without its own drawbacks, however. These are:

  • A lack of support for the plumbing. Hot tub plumbing is heavy, especially when filled with water. By encasing the plumbing in spray foam, full foam systems not only insulates the plumbing, it also helps to support its weight, leading to fewer potential problems over time.
  • The pumps can overheat in the warmer months. Trapping waste heat works great to reduce energy costs in the winter, but can cause pumps to overheat in the summer. To combat this, most hot tubs using perimeter insulation systems will include vents that can be opened up to allow some heat to escape the system.
  • Most perimeter foam systems utilize fibre board insulation. There are often small gaps in the insulation between the cabinet panels; reducing the overall efficiency of the insulation slightly.

3) Hybrid Insulation Systems

In an effort to combine the strengths of both full foam and perimeter insulation systems, some manufacturers have switched to a hybrid approach that utilizes two layers of insulation; one around the plumbing of the hot tub, and the other around the cabinet.

These systems typically either use a combination of spray foam and fibre board insulation, or thermal shield insulation. We typically prefer the ones that use the thermal shield insulation. This is because thermal shield is much better from a maintenance perspective. This is because thermal shield insulation won’t become saturated if it gets exposed to water; ensuring that your insulation is always running at peak efficiency.

The only drawback to thermal shield insulation is its R value. Each sheet of thermal shield provides the same insulating value as around 3″ of spray foam. This means that standard full foam hot tubs generally provide better insulating value if there is only one layer of thermal shield insulation in the hot tub. For that reason, thermal shield can really only be used effectively in hybrid systems that include multiple layers of insulation.

So Which Insulation System Is Best?

While each insulation system has it own pro and cons, on the whole we believe that the hybrid approach is best for hot tubs in Canada. It brings together the strengths of full foam insulation and perimeter foam insulation to maximize the energy efficiency of the hot tub, while also supporting its plumbing.

How Can You Improve Your Hot Tub Insulation?

A critical part of any hot tub insulation system is the insulating foam cover. Here are two ways that you can ensure that your cover is providing you with the best possible insulating value.

Check The Cover

A worn-out hot tub cover can easily cost you $100s in added energy costs over the course of a single winter. One of the best ways to maximizing your hot tub’s energy efficiency, therefore, is to ensure that your cover is working at peak efficiency. There are two things you should be looking for:

Is the cover sitting flat around the edge of the hot tub? To do their jobs effectively, hot tub covers need to form a tight seal around the edge of the hot tub. Without this seal, there will be significant heat loss around the edge of the cover.

Has the cover started to take on water? If the air pockets in the cover’s insulating foam start filling up with water, the efficiency of the cover will drop significantly; dramatically increasing your monthly energy costs. How can you tell if your hot tub cover has started to take on water? If your hot tub cover is significantly heavier than when you bought it, chances are that it has become waterlogged.

Add A Floating Thermal Blanket

Buying a floating thermal blanket is another great way to improve your hot tub’s insulation over the winter months. These are simply thin sheets of insulation that float on the surface of the water.

Most of the heat loss in a hot tub is lost through the cover (even if the cover is relatively new). By adding a 2nd layer of insulation to between the water and the cover, you can dramatically reduce this heat loss and decrease your monthly energy bill.

Wrapping Up

There are a wide variety of different hot tub insulation systems currently available in Canada. In our opinion, hybrid insulation systems (those that insulate both the outer cabinet and the plumbing of the hot tub) provide the best mix of insulating value and ease of maintenance. To ensure that your hot tub is working at peak efficiency (regardless of what insulation system it uses) we recommend regularly checking your hot tub cover, and adding a floating thermal blanket to ensure that the minimum amount of heat escapes through the cover.

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Whitby, ON L1N 2K6



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