Keep Warm Test for Electric Kettles

This test is part of How We Test Electric Kettles v1.0

Most electric kettles turn off automatically. But, how often do we get to the kettle straight after boiling? Besides, not every kettle has a 'keep warm' function, so that's why we test kettles for heat retention. Good insulation also saves on power costs, reboiling times, and improves general safety.

For these reasons, we do a heat retention test on all electric kettles by monitoring the temperature fluctuation for up to 5 minutes. Additionally, if you don’t want boiling hot water, this data can help you estimate how long to wait for things to cool down depending on the kettle you buy.

The Keep Warm test counts for 10% of the total Performance score.

Test Parameters

We use 1.5 liters of room-temperature tap water with a starting temperature of 80°F (26.7°C) for our boiling time test. After boiling, most electric kettles reach 99°C to 100°C without fail—and that’s the starting point of this Keep Warm test.

We simply set a countdown timer for 5 minutes and then use a two-probe digital thermometer to check the water temperature.

Steps

1. Fill the kettle with 1.5 liters of room-temperature tap water and plug in (we use a customized outlet as per our Energy Consumption test).

2. Turn on the kettle and make sure that the indicator light is on.

3. Once the kettle boils and automatically turns off, start a 5-minute countdown on a digital timer.

4. After 5 minutes, check the water temperature using a two-probe thermometer. Place one probe in the middle of the kettle and one probe closer to the carafe’s wall, both 1 inch above the heating plate.

5. Record the water temperature for data collection.

Scoring

Since 208°F / 98°C is basically just below boiling point, we use this as a benchmark for a 10/10 score. Each 2°F / 1°C drop will result in a one-point reduction.

This benchmark rightfully gives advantage to kettles that have temperature control. These kettles usually have a keep warm function that automatically holds the chosen temperature  once the kettle finishes running.

Kettles likely to have good heat retention are often made of ceramics, stainless steel, or have double-walled constructions.

We also considered the fact that the water temperature would drop by roughly 1°C once we opened the lid. However, this will also happen when you pour the water into a cup anyway, so we chose not to factor in this parameter.