How Mug Warmers Work

Want to keep your drinks warm down to the last drop? Mug warmers might hold the solution to a tepid glass of tea or coffee.
Want to keep your drinks warm down to the last drop? Mug warmers might hold the solution.
Nick Koudis/Getty Images

­When it's so easy to get distracted during a busy day, with work, chores and errands all jockeying for our attention, it's more than likely we sometimes upset some of the simpler pleasures in life.

For example, a mug of strong, freshly brewed coffee, or a cup of hot tea. Many like to start off their day (or even give a little extra kick to their afternoon) with these types of drinks, and most people drink them hot, or at least fairly warm.


But once you pour yourself a cup of tea or coffee and get ready to drink up the warmth to pleasantly heat your stomach, any number of things can happen to derail your attempts at comfort -- a phone call, a crying baby, a knock at the door. Within the shortest span of time, your attention is now redirected, and your mind starts to wander. Chances are you won't realize your unfortunate neglect until your eyes catch that still and tepid mug, now much less appealing than it was when it was nice and hot.

In most cases, people pour the substance down the drain and forget about making another cup. When the heat goes, so too can the taste. But what if this didn't have to happen in the first place? Fortunately for those of us who are either forgetful or like to stretch out our enjoyment of a hot drink, electric heat has made it possible to keep hot drinks hot, no matter how long you leave them unattended. You can buy a device called a mug warmer, which can keep your coffee, tea or any other kind of hot drink at a constant desired temperature with the help of a small electric heater.

So what's going on inside a mug warmer, and how does one transfer heat to your cup?


Mechanics of Mug Warmers

­Although there are various kinds of mug warmers made by different manufacturers, they're usually shaped like the drink coasters people use on tabletops to prevent water rings from damaging the surface.

Mug warmers resemble drink coasters, but they're thicker and generally have a slightly greater circumference than most drink coasters. They're typically designed for mugs, but you don't have to limit their use to just drinks. Other hot foods, like soups and stews, can stay warm if you pour them into a bowl and place the bowl on top of the device. Many designs have electric cords of varying lengths so you can plug the warmer into an outlet to receive power, but some models have a USB cable that lets you plug directly into a desktop or laptop computer for power, similar to the way you can charge an MP3 player with a USB port.


Mug warmers use heating coils in the same way electric kettles do. Once plugged in and switched on (most have an on/off switch on the side), electricity flows to a small heating coil built inside the device. A mug warmer works by using the simple properties of heat transfer and thermal energy. If we look at temperature on a microscopic scale, a material with a higher thermal energy just means the molecules in that material have a high kinetic energy and are moving around much faster than molecules in a cooler material. The molecules in a hot cup of coffee, for instance, are moving faster than the molecules in a cold cup of coffee. As the molecules collide, some of that energy transfers, warming up the cooler molecules and cooling down the hotter molecules in a process known as conduction. When you put your cool hands against a warm cup of coffee or tea, your hands will eventually get warmer because heat is transferring from the cup to your skin. So the mug warmer's coils transfer heat to the base of the mug warmer, and once you place a cup onto the device, the heat from the base will transfer to the cup and the liquid within.

So for the forgetful and the often overwhelmed, this handy device can keep coffee, tea, hot chocolate or soup at a constant, warm temperature without heating it beyond the boiling point.

For more information on other food conveniences, warm up to the links on the next page.


Lots More Information

Related HowStuffWorks Articles

  • Lueth, R.C. "Electric heating coil." U.S. Patent 4554441, 1985. (Feb. 16, 2009)
  • Peace, P.W. "Beverage warming apparatus." U.S. Patent 4463664, 1984. (Feb. 16, 2009)
  • "The principles of heat transfers." (Feb. 16, 2009)
  • "What is an electric mug warmer?" (Feb. 16, 2009)