A cooler is usually used to keep food and drinks cold but the same insulation can be used to keep food warm for an extended period of time. But exactly how long will a cooler keep for warm?
A cooler can keep food warm for 4-6 hours but this can be extended by using aluminum foil and a heat source like a hot water bottle or hot bricks. Make sure to preheat your cooler and not to put cold food with hot food.
Not all coolers have been built the same. This is a determining factor as to how long you can keep food warm in one. Coolers have a wide range when it comes to insulation and some coolers perform a lot better than others.
Generally speaking the better a cool is at keep ice cold the better it's going to also be at keeping things warm.
A Note on Health and Food Safety
Keeping food hot using a cooler can work really well but you need to be really careful about food safety so you don't get sick.
Warm (but not hot) food is a perfect breeding ground for harmful bacteria and you obviously want to avoid this.
According to the USDA there is a “danger zone” for food between 40-140ºF (4-60ºC) that you want to avoid. When keeping food hot for an extended period of time this means you'll likely want to keep it ABOVE 140ºF (60ºC)
If you don’t consume the food you’re trying to keep warm quick enough after it has reached the danger zone, bacteria will grow and the food will spoil in the cooler. It is suggested you store your food hot and eat it within a couple of hours of it dropping to the danger zone or a little below.
Things You Can Do To Keep The Heat
Here are some life hacks when it comes to keeping food hot in a cooler. Some of the tactics are common sense while others are a little more scientific.
I've done a full article on the best ways to keep food hot in your cooler but these little tips will help your food stay warmer longer.
Preheat Your Food
You need to make your food hot to be able to keep it warm. Coolers do not have a heating element, hence, they only can keep food warm and not heat it.
Cook It Hotter
The food you plan on eating at a later time can be cooked and prepared hotter than usual. This is because the food will cool off over time.
Up The Cooler’s Thermal Mass
The more dense your food is, the more thermal mass it will have.
This is why water stays hotter for longer than a piece of toast, for example.
Just like how freezer packs keep things cold, hot packs keep things hot.
You can fill water bottles and other containers with hot water to get hot packs to put in your cooler.
Everything needs help to reach its full potential. Using coolers to keep things warm is no different. Increasing insulation with dish towels, towels, cardboard and such things can maximize the cooler’s potential.
Decrease Air Space
The space in your cooler will steal heat from the food you are trying to keep hot. Fill this space with towels or even clothes to decrease the air space and increase the insulation of your cooler.
Evaporation takes with it lots of heat from your hot foods and drinks. The steam we are all familiar with is a huge heat hog. Try wrapping your hot food in tin foil or such things so prevent the steam from stealing your food heat when it escapes.
Preheat Your Cooler With Hot Water
You can’t use boiling water to warm the walls of your cooler unless you are okay with risking the cooler’s walls and warping them or possibly damaging the insulation. More on using boiling/hot water in a cooler.
Use warm water to fill the cooler up and leave it for around twenty to thirty minutes to allow thermodynamics to do its thing and heat up the insulation of the cooler. Remove the water and then use a towel to dry the inside.
Aluminum Foil Assistance
Coolers have not been known for keeping things warm since they are called COOLers. Heat radiation (a type of heat transfer) is not usually a part of a cooler’s design. Aluminum foil is used to insulate and reflect heat radiation. Wrap a few layers of the aluminum inside.
Don’t Mix Hot and Cold
To prolong the warmth of the food in your cooler you should not put cold things in with hot things you are trying to keep warm. They will exchange their temperatures until the cold things are warm and the warm things are cold.
Thermoses and Friends
If you are transporting soup or anything like that, Thermoses and thermal bags are a great way to keep food warmer for longer in a cooler.
Crockpot in a Cooler
If you made your food in a crockpot, it might be easier to just line your cooler with towels and place the crockpot directly in the cooler. The crockpot will already have its own kind of insulation. Fill the empty space with more towels.
Hot Bricks for Hours
One easy, ingenious, and cost efficient way to maximize your cooler’s ability to keep things warm for hours is to use hot bricks.
Wrap some bricks up in aluminum foil and bake them in the oven for about twenty to thirty minutes and wrap them in towels to place in the cooler.
Close The Lid
Closing the lid is an obvious way to keep food warm in a cooler for longer. Reduce the number of times you open the lid as much as possible so you don’t let the precious heat out.
Coolers With Aux Warmers
If you need to transport your hot food over a few hours’ drive, there are twelve-volt car adaptors that you can plug in and heat your cooler with.
You can also use these to turn your cooler into a crock pot or slow cooker.
Higher End Coolers
The best-selling coolers with the best insulation are manufactured by Kong.