Most caregivers don’t need a bottle warmer. You might think this device would take time and guesswork out of heating a bottle for a hungry baby, but after researching 25 bottle warmers and testing 15 since 2017, we’ve concluded that even the best of them are only modestly more convenient than simply warming a bottle in a bowl of hot water.
But a dedicated warmer could benefit some people, including those who are heating multiple bottles at a time, as well as those who enjoy the convenience of a programmable device. We spent 10 hours warming 50 bottles of formula in early 2024, and we’re confident our longtime pick, the Kiinde Kozii, is still the best option.
1.Kiinde Kozii Bottle Warmer
This warmer is the most efficient and reliable of those we tested, and it’s one of the few that doesn’t need fresh water every cycle. But it can still overheat milk and the cleaning process is involved.
The Kiinde Kozii consistently heats bottles close to our expert-recommended temperature of 98 °F (i.e., about body temperature) without overheating and offers a high degree of control with a simple turn of the dial. The Kozii uses a flowing 135-degree circulating water bath (instead of a still water bath like other warmers), which transfers heat more efficiently. While it’s possible to overheat bottles using the Kozii, as with any warmer, the water bath empties into a reservoir as soon as the heating cycle is complete, so the chance of overheating bottles is less than with other devices.
2.The First Years Simple Serve Baby Bottle Warmer and Sanitizer
It’s the fastest warmer we tested, but you have to add an exact amount of water for each use, parts come out hot, and it takes some experimenting to get the right temperature.
If you want an affordable bottle warmer and don’t mind some trial and error, the steam-powered The First Years Simple Serve Baby Bottle Warmer and Sanitizer is a good fit. The Simple Serve lacks many of the conveniences of the Kiinde Kozii, but it delivers warm breast milk and formula more quickly than any other bottle warmer we tested. Compared with our top pick, the Simple Serve is more challenging to fill—you use a tiny plastic vial to add a set amount of water each time. And although it’s efficient, reliably heating bottles in 3 to 4-and-a-half minutes depending on size and shape, it takes some effort to determine the correct heating cycle time. And you can’t use this warmer with glass bottles.
How we picked and tested
Based on our research, we determined a good bottle warmer should:
Heat milk efficiently, without overheating: A good bottle warmer reliably heats milk or formula without overheating or developing hot spots. It’s possible to overheat a bottle in any warmer by choosing too lengthy of a cycle, or by leaving the bottle in the warmer for an extra minute or two. This is because even warmers with an auto-shutoff remain warm, though not hot. To avoid burns and altering the bioactive properties of breast milk, the best bottle warmers do not allow milk or formula to exceed 104 °F. It takes approximately 7 minutes 30 seconds to heat an 8-ounce bottle of refrigerated formula using a bowl of hot water (about 150 °F); we looked for warmers that came close to that time.
Fit a range of bottle types: Babies can be fickle, and some go through a period of preferring one bottle shape or size over another. The best bottle warmers accommodate a range of bottle types, models, shapes, sizes, and materials, including short, squat bottles; narrow-neck bottles; and those made from plastic, silicone, or even glass.
Be intuitive to use: Simple-to-set timers and controls, and a clear signal to let you know when the heating cycle is complete, make bottle warmers easier to use. The best ones have an automatic shutoff and/or internal thermostat that prevents bottles from becoming too hot.
Allow back-to-back cycles: A bottle warmer that accurately and efficiently heats more than one bottle in quick succession without having to unplug, add cold water, or wait to let the heating element cool is helpful for busy, tired parents of multiples or two kids under 2 years old.
Be relatively easy to clean: All bottle warmers require some care in order to avoid mineral buildup from tap water. The process varies; most require that you clean the interior with warm, soapy water every two to three days and descale the unit by filling it with a mixture of water and distilled white vinegar every two to four months.
Provide a good value: Baby gear can be pricey and may only come in handy for one to two years. We looked for ones that are durable enough to be resold or saved for use with a future baby.
In early 2024, we tested nine bottle warmers using four of the leading bottle brands and models We first evaluated the bottle warmers to see how easy each was to assemble and use. We then noted whether they accommodate a range of bottle types, and whether they could also heat frozen breast milk pouches and baby food.
We next put the bottle warmers through a test using a probe thermometer. We prepared and refrigerated the formula until it reached between 40 °F and 50 °F. We filled small bottles with 4 ounces of formula and large bottles with 8 ounces of formula. At the beginning of each heating cycle, we placed the probe near the center of each bottle, halfway deep into the liquid. We then tracked the temperature of the formula as it heated, recording the temperature every 30 seconds. At the end of each cycle, we recorded the temperature at the surface of the milk (the surface temperature tended to be several degrees warmer than the center, as warmer liquid rises above cooler liquid) and the time it took to heat the bottle. In researching safe use, we learned that bottle warming should never take more than 15 minutes to guard against possible bacteria growth, according to the experts we interviewed.
We next swirled the bottle gently five times and took the temperature at the center of the milk. We finally gently shook the bottle for about 30 seconds more and noted the final temperature. (Most warmers instruct you to swirl the bottle for 30 seconds after the machine’s cycle ends.)
Once we narrowed the field to two top warmers, we used them to heat bottles of breast milk. We found that breast milk bottles heated at similar speeds to formula bottles.
