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Backpacker Magazine – Online Exclusive

How to Preheat a Thermos

Maximize your thermos's heat retention capacity with these easy preheating steps.

by: Genny Fullerton

(Photo by Julia Vandenoever)
(Photo by Julia Vandenoever)

Step 1. Boil the water.

Step 2. Pour some water in the thermos. How much depends on how hot you want your beverage or how quickly you want it. If you’ve got time, you can put just a few inches of water in, secure the cap, and the steam will heat up the rest of the thermos within a few minutes. I let it steam while I’m packing the rest of my food/snacks and getting the last minute things packed up. This is the "green" method because it uses less water. If you need your hot drink ASAP, fill the whole thermos with boiling water and the water will heat the thermos in just a minute or two.

Step 3. When your thermos is hot, or after the allotted time indicated above, pour the preheating water out and fill your thermos with the hot beverage of your choice.



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READERS COMMENTS

mikebam
Nov 18, 2012

The one thing your leaving out with the 2 ice trays in the freezer theory is that the hot water ice tray only freezes the outside faster than the cold water. It still takes the hot water longer to freeze into an entire cube of ice than the cold water.

jim smith
Jan 24, 2012

untrue. ive worked outside everyday for the last ten years, and i can say that the difference between preheating and not preheating is usually 4/5 hrs of hot beverage time. i usually fill mine with the hottest tap water possible the night before, and this assures me steaming hot coffee all day(ten hours)

Alan
Dec 22, 2011

In very special circumstances, hot water can freeze faster than cold water. That is not the issue here though. The idea is to heat the closed mass of air in between the double walls. This increases the insulating properties and keeps your drink warmer longer.

GEORGE LINCOLN COLE
Sep 19, 2011

WHY DOES THIS MYTHOLOGY CONTINUE? GETTING THE OUTSIDE JACKET OF A VAC/BOTTLE THERMOS HOT IS THE QUICKEST WAY TO GET IT'S CONTENTS COOLED. WHEN TWO ICE CUBE TRAYS ARE PLACED IN A FREEZER[1]HOT [2]COLD THE HOT ONE FREEZES FASTER THAN THE COLD ONE. PLEASE STUDY THERMODYNAMICS BEFORE YOU REPEAT THIS ERROR.

GEORGE LINCOLN COLE
Sep 19, 2011

WHY DOES THIS MYTHOLOGY CONTINUE? GETTING THE OUTSIDE JACKET OF A VAC/BOTTLE THERMOS HOT IS THE QUICKEST WAY TO GET IT'S CONTENTS COOLED. WHEN TWO ICE CUBE TRAYS ARE PLACED IN A FREEZER[1]HOT [2]COLD THE HOT ONE FREEZES FASTER THAN THE COLD ONE. PLEASE STUDY THERMODYNAMICS BEFORE YOU REPEAT THIS ERROR.

GEORGE LINCOLN COLE
Sep 19, 2011

WHY DOES THIS MYTHOLOGY CONTINUE? GETTING THE OUTSIDE JACKET OF A VAC/BOTTLE THERMOS HOT IS THE QUICKEST WAY TO GET IT'S CONTENTS COOLED. WHEN TWO ICE CUBE TRAYS ARE PLACED IN A FREEZER[1]HOT [2]COLD THE HOT ONE FREEZES FASTER THAN THE COLD ONE. PLEASE STUDY THERMODYNAMICS BEFORE YOU REPEAT THIS ERROR.

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