How to Choose the Best Bottle Warmer

Buying Advice
By Ruth and Ben Traxler, Lindsay Ellis & - Tuesday June 28, 2016
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During use, the water level rises up into the warming chamber of the Kiinde and creates a gentle, circulating warm water bath. After shut off, the water drains back into the hidden water reservoir.
Credit: Ruth and Ben Traxler
In our Bottle Warmer Review, we put seven of the most popular bottle warmers to the test and rated them on qualities such as health and safety, warming efficiency, ease of use and ease of cleaning. Through this testing, we distilled down important qualities you will want in any bottle warmer; the Editors' Choice Kiinde Kozii and Best Value Chicco NaturalFit Two-in-One are the cream of the crop. This buying advice guide explains it all in further detail.

Complimenting the bottle warmer review is our Baby Bottle Review and Best Practices for Handling Breast Milk.

Why Purchase a Bottle Warmer?


While a bottle warmer is by no means a necessity, if you're warming more than one or two bottles a day or your baby prefers for milk to be just the right temperature, then you may find it convenient to have one that is designed to safely, easily and consistently heat a bottle.

The bottom line is that a bottle warmer is a convenient time-saver, but it is not a must-have baby product. So, lets start by looking at the alternatives side-by-side to help you assess whether the cost justifies the convenience of a bottle warmer.

Avoid Overheating Breast Milk
Breast milk starts degrading in nutritional and immunological value at 104 F / 40 C, but deterioration accelerates as temperatures climb higher than 113F/45C. You should aim to warm baby's milk to approximately 98.6 F / 37 C, body temperature, or less.

Three Ways to Warm a Baby Bottle


It's the middle of the night. Baby is hungry and it's your turn to feed him. Time for the midnight shuffle. Do you grab the baby and then go warm the bottle or vice versa?

Good options for warming the bottle include:
  • Stand at the sink while swirling the bottle under warm tap water (not too hot)
  • Put the bottle into a bowl of warm water with intermittent swirling (again, not too hot)
  • Use a bottle warmer

The first two options require constant attention which is asking a lot when you are half asleep with a hungry crying baby. The advantage of a bottle warmer is that your hands are free and you can focus on baby's additional needs like a diaper change or sweet cuddle time.

Is it worth it? That's a personal decision, but many parents find the convenience to be worth the cost.

No Microwave, No Boiling Water
Never use the microwave to heat baby's meal, whether it be formula, breast milk, or purees. High, focused heat generated by a microwave can results in dangerous "hot-spots" in both liquids and solids. If not properly mixed, cooled, and checked, this can result in scalding injury to baby. In addition, a microwave is likely heat at least some, if not all, of the breast milk above 104 F / 40 C, the temperature at which beneficial enzymes, nutrients, and antibodies begin to degrade reducing healthful benefits for baby.

Furthermore, do not put a bottle in a pan of boiling or even just boiled water (even if the stove top is off), as this is likely to result in overheating too.

Selecting the Right Product


Apart from convenience of being hands-free when warming the bottle, a great bottle warmer should deliver on the following five factors:
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    Happy baby! Nothing's better than a warm meal in the belly.
    Credit: Lindsay Ellis
    Health & Safety — Avoiding risk of burn injury as well as providing nutritionally intact breast milk at an appropriate temperature for baby is essential. Generally, a good rule of thumb is to heat to near body temperature 98.5F/37C and not much higher. More on this below where we discuss Preserve the Full Nutritional Value of Breast Milk.
  • Efficiency — Ability to warm breastmilk or formula quickly and consistently
  • Ease of Use — Easy to operate and maintain
  • Versatility — Accepts narrow or wide-mouth bottles of any material
  • Portability and Footprint — Taking warmer on the go and use of counter space

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To test the temperature of a bottle's heated contents, we held a professional grade digital thermometer in the center of the bottle recording temperatures throughout the warming cycle and for several minutes after the unit's shut-off.
Credit: Ruth and Ben Traxler

Preserve the Full Nutritional Value of Breast Milk


As we describe in more detail in our related article, Best Practices for Handling Breast Milk, your breast milk is "liquid gold" in terms of its nutritional value to your baby. Yet, that nutritional value can be degraded by overheating.

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Overheating breastmilk can cause nutritional degradation. (X-axis in minutes, Y-axis in degrees Fahrenheit)
Credit: BabyGearLab

Once breast milk is warmed to temperatures higher than 104 F / 40 C, its nutritional and immunological value begins to deteriorate, both of which are crucial to baby's health and immunity. However, degradation does not become severe until temperatures rise above 113F / 45C. For example, after 10 minutes at 113 F / 45 C, a study conducted by University of Manchester, UK breast milk showed a loss of 10% of key nutritional activated enzymes. But, even just 1 minute at 131 F / 55 C resulted in a 50% loss of activated enzymes. Yet no significant loss occurred after 20 minutes at 104 F / 40 C (or lower temps).

Luke Warm, Not Hot


Keep in mind that the ideal target for breast milk temperature is about body temperature or less, 98.6 F / 37 C, and less is fine. This is not very hot at all, really just luke warm.

Options and Features


Bottle warmers come in all shapes and sizes and use different methods to actually warm your baby's meal. Outlined below are key features to look for when selecting a bottle warmer.

Water Bath Versus Steam Heat Technology


Bottle warmers use water in one form or another to heat a bottle. Some warmers use a warm water bath while others use steam heat.

Water Bath


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During use, the water level rises up into the warming chamber of the Kiinde and creates a gentle, circulating warm water bath. After shut off, the water drains back into the hidden water reservoir.
Credit: Ruth and Ben Traxler
We recommend a bottle warmer that uses water bath technology. While they tend to heat slower, they heat consistently without the high temperatures required to produce steam. A water bath based warmer heats breastmilk or formula gently by circulating warm water around the bottle. The benefits reaped here are that this gentle warming helps breastmilk retain maximal nutrients, maternal antibodies, and likely other health promoting factors. We also consider it safer as the water used is warm rather than hot and potentially scalding steam. As mentioned, these usually take more time to heat than steam versions. But here, patience will pay off.

Of the bottle warmers we tested, the Editors' Choice Kiinde Kozii, the Best Value Chicco NaturalFit Two-in-One, and the Philips AVENT Fast employ use of a water bath in their warming process.

Steam Heat


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Cuisinart BW-10 warming chamber with grey colored heating element below plastic warming basket. Steam is produced when water on the heating element reaches boiling point. Remove basket to easily access the hot plate for drying and cleaning. Descaling is required once a month by adding a vinegar soak.
Credit: Ruth and Ben Traxler
With steam heat, water placed inside a reservoir comes into contact with an internal heating element (like a hot plate) producing steam which in turn heats liquid contents. The warmers in our review that employ steam heat technology are the Dr. Brown's Deluxe, Born Free Tru-Temp, Cuisinart BW-10, and the Boon Orb, .

While usually heating faster than water baths, hot water and scalding steam rise up to very high temperatures. The result? A bottle's exterior is usually very hot upon finishing a heating cycle, typically necessitating a cool down prior to being held. In our opinion, these high temperatures carry unnecessary risk. If spillage of warmer contents were to occur, risk of burn injury is present. In addition, steam does not always heat evenly. This means that significant temperature variations may exist throughout the contents of a heated bottle and without thorough mixing and checking, hot-spots are a risk.

Lastly, because steam heat typically generates such high temperatures, there is increased potential for nutritional degradation of breastmilk if brought to temperatures >104F/40C. What we found in our warmer testing is that a few of the units we tested make it far too easy to overheat breast milk, which results in a significant loss of nutritional quality.

Versatility


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Sadly, the Dr. Brown's Deluxe doesn't fit Best Value Tommee Tippee Feeding or Top Pick Comotomo.
Credit: Ruth and Ben Traxler
Baby bottles can be narrow or wide and short or tall. As such, they may not necessarily inside the a bottle warmer's chamber. Additionally, material limitations may mean that a certain warmer isn't compatible with a particular baby bottle.

In our testing, we found that the Dr. Brown's Deluxe and the Cuisinart BW-10 didn't fit the widest of bottles like the Comotomo and the Tommee Tippee Feeding.

In addition, some bottle warmers require either plastic or shatter-resistant glass like borosilicate found in Lifefactory because the quick heating process may cause the glass to break. For example, the Boon Orb should not be used with glass bottles…period.

Because it is uncertain which bottle type and nipple your baby will prefer, choosing a bottle warmer that will accommodate all bottle sizes and materials is important. Both the Kiinde Kozii and the Chicco NaturalFit Two-in-One are great choices for versatility and fit every bottle, tall or wide, that we tried.

Auto Shut-Off Feature with Timer


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The lit LCD control panel on the Dr. Brown's Deluxe is has a visual count-down timer, letting you know how long you'll have to wait until the bottle is ready.
Credit: Ruth and Ben Traxler

We highly recommend buying a bottle warmer with an auto-shut off feature which means that it turns itself automatically. The only warmer in our review that does not include this feature is the Philips Avent Fast.

Most warmers shut off automatically based on either a timer or a temperature reading. In our testing, the timer-based, auto shut-offs were reliable and easy to use and read. And, it's helpful to know how much longer you'll need to wait. Timers allows for some adjusting and once you've found the time setting that's best for your baby, it's easy to remember for next use. The Dr. Brown's Deluxe and Born Free Tru-Temp even have a memory for the previous setting.

Though a temperature-based shut-off sounds ideal, we found that this method didn't work as well in practice often overheating or under-heating bottles. The one exception is the Chicco NaturalFit Two-in-One which with its temperature-based system heated consistently to a good temperature without going over 100F/37.8C.

Audible End Beep


An audible beep at auto shut-off is important because it is easy to get side tracked with baby while a bottle is warming. And, in many of the warmers we tested, the temperature of bottle contents will continue to rise if left in the warmer after auto shut-off. This can mean overheating. Because breast milk begins to degrade significantly above at 113F/40C to 45C, removing a bottle promptly when done is important.

Water Reservoir


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Born Free Tru-Temp's water reservoir is easy to refill and install, but watch out for water spillage. We found that it lasted for 1 to 2 days, depending on usage frequency.
Credit: Ruth and Ben Traxler
Some warmers require that you add water each time, while others have a built-in reservoir that monitors the water for you, and lasts through several cycles. Warmers like the Kiinde Kozii, Chicco NaturalFit Two-in-One, Dr. Brown's Deluxe, and the BornFree Tru-Temp, and do not require a refill for every use which will save valuable time and effort.

Making Your Selection


Taking into account the various features and options available, we scored each of the 7 warmers in our review on the following four metrics: health and safety, warming efficiency, ease of use, and ease of cleaning. These are all important factors that should be considered during your buying process.

Warming Efficiency


Since a bottle warmer's main purpose is to provide your baby with a comfortably warm meal, this was a high priority in our testing. We wanted to be sure that we could toss a bottle in, tend to baby, and return to a just-right meal every time. Some of the warmers were capable of producing a consistently warmed bottle with each use, while others, like the Philips Avent Fast, varied in their results, sometimes leaving us with in an overly hot or still cool bottle. Your time is precious so we urge you to consider a warmer capable of getting the job done consistently with each use.

Ease of Use


Before a bottle warmer can fit seamlessly into your routine, you have to learn how to use it. Out of the box, the warmers we tested included a wide variety of "parts", ranging from one solid unit like the Kiinde Kozii, to a unit plus a bunch of extra pieces, like the Cuisinart BW-10, leaving you with quite a task on your hands. The easiest to use warmer in our testing was the Editors' Choice Award winning Kiinde Kozii; a simple, one-piece unit that didn't require a lot of prep or maintenance.
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This warmer has a compact footprint, is light at 1.5 pounds, and fits both narrow and wide mouth bottles. Here in use with Editors' Choice Lifefactory baby bottle.
Credit: Ruth and Ben Traxler

On top of assembly, there are charts included with the units that use timers to help figure out the length of a warming session. These charts range from super simple to majorly complicated. What we found after having navigated each warmer's manual was that no matter what, using a bottle warmer will involve a bit of a fiddle factor. Many of the instructions account for different bottle types and sizes, as well as room temperature, cold or frozen milk. It's important to be aware that you will inevitably go through some trial and error before you consistently reach the perfect setting for the particular bottle and starting milk temperature that your baby uses most often. And that's ok! But it shouldn't take more than a day or so of fiddling (and hopefully less) to get your machine working how you (and baby) like. Just keep this in mind as you scope out potential warmers.
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The Cuisinart BW-10's warming guide is easy to read and can be found in the directions as well as printed on the backside of the unit.
Credit: Ruth and Ben Traxler
You'll also want to think about the type of bottle you'll be using. As we mentioned above, some warmers don't fit extra-wide based bottles like a Tommee Tippee. Other bottle warmers, like the Boon Orb and the Cuisinart BW-10 offer adapters for wide-mouth and narrow bottles. We found that the Kiinde Kozii and the Chicco NaturalFit Two-in-One worked the best with all bottle types.

Another handy feature we appreciated was those warmers that included a "basket" for removing the bottle or jar of baby food in case it becomes too hot to handle. A few of the warmers we tested got carried away with the steam and would overheat the bottle itself, leaving it very hot and difficult to remove, so a basket was nice. We liked the baskets in the Boon Orb and the Cuisinart BW-10.
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Turned on, the Orb emits a mellow blue light from the on/off button. Here, with baby food warming basket installed.
Credit: Ruth and Ben Traxler
Lastly, you'll want to be aware that many of the warmers have a recommended wait time between running warming cycles consecutively. Being able to start another warming cycle immediately would be very important if you were heating two or more bottles in a row, say for twins. It's also handy if the first cycle doesn't quite get the milk warm enough and you need to add just a bit more time. The longest wait time we found between uses was 15 minutes (or until the unit cools down), and this was with the Chicco NaturalFit Two-in-One. This could be a serious hassle in some cases.

Ease of Cleaning


This metric is pretty self explanatory, but definitely something you'll want to consider. Although cleaning isn't always a per-use or even daily requirement, there is a certain aspect involved with keeping this type of product in proper running order. We found, that unless you spill milk on the unit, this really comes down to proper maintenance. Since this type of product uses water in some form or another to warm the bottle, the issue lies in mineral deposits forming someplace on the unit, usually in the warming chamber and/or on the heating element.

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The warming chamber and warming plate (in view at the bottom of the chamber) need to be cleaned (de-scaled) periodically by adding a vinegar soak to the unit.
Credit: Ruth and Ben Traxler

Every warmer we tested instructs you to use a vinegar solution rinse on occasion (also called descaling) to get rid of these deposits. We also found that the warmers which use a reservoir system carry a higher risk for mold or mildew build-up within the reservoir itself. It is recommended that those units be cleaned out a little more often to try and avoid the possibility.

Conclusion


We hope that the addition of a bottle warmer to your personal baby gear line-up will help things run a little more smoothly at your house. Although it may take a few tries to get to that perfect setting, once you're there, your warmer should perform safely, consistently, and make life with baby just that much easier!
Juliet Spurrier, MD
About the Author
Dr. Juliet Baciocco Spurrier is a board certified pediatrician, mother of two, and founder of BabyGearLab. Juliet earned her Bachelor of Arts degrees in Anthropology and Italian Literature from the University of California at Berkeley and her Medical degree from Georgetown University School of Medicine in Washington DC. She completed her pediatric residency at the Doernbecher Children's Hospital at Oregon Health & Science University in Portland, OR, and subsequently practiced pediatrics in both the Pacific Northwest and Silicon Valley. Juliet serves as Mom-in-Chief at BabyGearLab, where she oversees all baby product review activity, assuring that each review delivers on our commitment to quality.