Hotronic S4 Boot Heater Review

Product: Hotronic S4

Our Rating: 4.9/5

Overview: If you’re someone that struggles with cold feet, the Hotronic S4 is a product that’ll help you out. This heater can be used during many activities including skiing, hunting, cycling, fishing, hiking and more. The S4 is most commonly used for skiing, however.

There’s many great features too, including:

  • 4 heat settings
  • 178 degrees of warmth on the highest setting (84 degrees on low and temperatures in between)
  • 21 hours of heat on the lowest setting
  • Installs in all footwear and is one size fits all

and more!

This is one of the most popular boot warmers available and is also one of the highest quality. If you’re serious about purchasing one of these products, I would definitely consider the Hotronic S4.


Video Review:

Here’s a video that goes over this product in depth:

Now you know why I think so highly of it!


A Complete Universal Package

The S4 Ski Boot Heater comes in two variants: Custom, and Universal. The only difference between the two is that Custom package does not include a universal insole. Custom is meant for folks who want to install the heating elements onto their own custom footbeds or orthopedic insoles.

With the Universal S4 Package, you get everything you need to install the boot warmer into any boot or winter footwear out there. This package contains a universal insole. You can replace the existing footbed inside your ski boot with this one.

All S4 Ski Boot packages come with a pair of heating elements, battery packs, covers+strips, and a recharger as well. It has pretty much everything you need to install the warming system inside your ski boots.


Compact, Adhesive Heating Elements

A pair of ultra-thin heating elements handles the main task of the S4 system. These are a pair of circular/oval disks, with a slim charging wire attached to them. You will be putting one of each into the insole of your boot (or the universal insole that you get with the package).

The heating elements are small enough to fit comfortably on any insole or footbed out there. Do note that these are compatible with adult sizes only. There are two potential spots where you can place these elements. The most common spot is the ball of the foot, just below the toes.

The heating elements have an adhesive coating on one side. This allows them to attach to any insole or footbed securely. You could also stick them to the heel of the insole if you feel that the heat should be focused there.

Though they are compact enough to fit on an insole, the oval shape allows these elements to deliver heat over a wider area.


Cambrelle Covers/Liners

Once you place the heating elements onto the insoles, you need to cover them with an appropriate liner. Hotronic has opted for Cambrelle as their material of choice for this purpose. They could not have chosen a better material here.

Cambrelle is made up of a dual-nylon fiber construction. This non-woven fabric is the gold standard when it comes to the linings of outdoor boots and hiking shoes. It has several qualities that make it the perfect choice for high-activity footwear.

Cambrelle liners have superior moisture management properties. When your foot is inside the shoe or boot, these moisture-wicking fibers take the sweat away from your skin, keeping it dry and comfortable. Once your shoes are removed, the moisture is allowed to air out.

The Hotronic S4 Cambrelle covers are designed to sit snugly above the heating elements on your insole. These covers are made in the shape of an insole, and come several sizes larger than usual. This allows you to get the perfect fit once you stick them onto the insole/footbed, and trim off the edges.

And yes, the covers have sticky adhesive on the underside. You can quickly attach these on top of your insoles and heating elements. The lining distributes the heat equally across all the zones of your feet. This is important since the elements do not cover the entire feet.


Heatready Insoles

This component is only available in the S4 Universal version. If you buy the Custom package, you will not get the soft Hotronic insoles. These red colored insoles are designed specifically to work with the heating elements and wires. If you use these, you will not have to make any alterations with a razor to your current insoles.

The insoles are made from soft EVA foam. They are incredibly compact and weighs just 3 ounces. They have a one-size fit all design. That just means that these are oversized. You can trim them down to your ideal size using a razor.


Compact Battery Packs

Those flat wires from the heating elements lead to a pair of battery packs, one for each boot. The S4 battery pack is designed to be attached to the sides of your boots. They come with clips that can connect to the top of your boots. You may also buy Hotronic mounting brackets separately if necessary.

These are NiMH cells, in the AA format. They are rechargeable batteries, explicitly chosen due to their operating characteristics. NiMH cells are safer than the popular Li-ion and Li-po batteries. We have all heard stories about cell phone batteries exploding dangerously. That risk is far lower in NiMH cells.

NiMH is also better than many other batteries in cold weather. Since you will be using the S4 almost exclusively in the snow, it makes sense to have the battery packs using NiMH cells.

They also lack the dreaded “memory effect,” which commonly affects the NiCad batteries. The memory effect is a condition where a rechargeable battery capacity is reduced when it is frequently charged before it becomes empty. NiMH rechargeable cells do not suffer this issue. So you can safely charge them at any time.


Multiple Heat Settings

Like many advanced wearable heating systems, the Hotronics S4 also has a customizable heat setting. But unlike the usual three temperature settings you often see on heated gloves and boots, the S4 has an extra setting as well. Here is a quick breakdown of the three settings:

  • Level 1 – between 84 to 98 degrees F
  • Level 2 – from 107 to 121 degrees F
  • Level 3 – from 122 to 138 degrees F

The temperature range offered by this heating system is adequate to cover most winter skiing conditions out there. Now let’s try to explain the fourth setting. Levels 1 to 3 can be set to provide continuous heat. Level 4 is designed to give a short burst of high temperature, between 158 to 173 degrees Fahrenheit.

This is usually when your feet need an extra bit of warmth, in really cold conditions. On the default setting, Level 4 will only be initiated intermittently, in 3-minute intervals. It provides a quick burst of heat. But you can also set Level 4 to deliver continuous heat. But at those temps, it may lead to burns.


Easy Controls & LED Indicators

The control buttons for the system is located on top of the battery packs. There are two buttons, with a series of red LEDs in between. The four LEDs clearly indicate the current heating level being used by the S4 system.

You can increase or decrease the temperature setting using the two buttons. The red LEDs work as highly effective indicators, even in low visibility conditions. They also tell you if the system is powered on or turned off. When you set the Level 4 heat setting to run continuously instead of burst mode, the LEDs will blink in warning.


High Capacity Battery Packs

As usually seen in a device with custom heat settings, the battery performance is directly linked to the usage patterns. If you set the system to run on high temps, you will get a far lower battery life than usual. Here is a rough estimate of the battery life provided by the NiMH cells with the different heat levels in the S4:

  • Level 1 – average battery life of between 16 – 21 hours
  • Level 2 – average battery life between 7 – 10 hours
  • Level 3 – average battery life between 5 – 7 hours
  • Level 4 – between 2 – 4 hours

With moderate use, these batteries can keep your foot warm for an entire day. If kept in the lowest setting, you could conceivably get two days worth of use.

These NiMH cells are quite long lasting as well. They can retain 95 percent of their original capacity, even after four years of idle time. If you leave the system in storage during the summer, it will still be alive and kicking the next time winter comes along!


Universal Recharger

The charging system provided along with the S4 Ski Boot Heater is exceptionally flexible. The adapter comes with two interchangeable plugs, one for US-style wall outlets, and one for European style outlets.

One really convenient feature is the ability to charge both batteries simultaneously. The adapter has two connectors for this purpose. So after an entire day on the slopes, you can just leave both battery kits on the charger overnight.


Easy Installation

The S4 Heating system is designed for hassle-free installation. All you need to get this thing inside your ski boots is a sharp razor and some duct tape. In some boots, they already have the slits and straps in place for a heating system.

If your boot does have these features, all you need to do is remove the insole, attach the elements and Cambrelle liner, string the battery cable through the slits, and you are good to go.

Even in the case of boots that do not have these slits/ports, the whole process of prepping the insole and liners can be completed in under ten minutes. There are several detailed YouTube videos that describe the process. It is also quite easy to remove the heating system and install it in another boot/footwear.

You’ll Love This Heater!

The Hotronic S4 really is one of the best heater on the market and is loved by so many people – there’s a reason it’s one of the most high selling.

Any person that suffers from cold feet will love this product and this is true for skiers, hunters, hikers and more.

If you want to see how much this heater will cost you, click the link below:

This isn’t the only heater for skiers too. You can see my top picks for the year by clicking below:

My Favorite Ski Boot Heaters

Are you excited to have warm feet this winter?

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