Coolers can be a great way to keep food hot and by adding hot bricks in your cooler you can keep food hot for hours or even days at a time.
Hot bricks are simple to make, cheap and are super effective at radiating heat over a long period of time to keep for extremely hot so you can eat it later.
But you do need to take some precautions so you don't burn yourself, ruin your cooler completely or have your food go bad.
To make hot bricks for a cooler take bricks and wrap them in aluminum foil. Bake them in the oven at 300ºF (150ºC) for 20-30 minutes or longer. Wrap them in a towel and place at the bottom of your cooler and place food on top. These will stay hot for 6+ hours.
Step-By-Step How To Make Hot Bricks For Your Cooler
Making hot bricks for you cooler is actually really easy. Here is the step-by-step guide.
1. Choose Your Bricks or Rocks
Firstly choose the bricks you want to use in your cooler.
Bricks range in size and shape but basically any brick will do.
Ideally you want to avoid bricks with lots of holes in them as these air gaps means there is less hot brick overall and less heat in your cooler.
The complete bricks without holes stay hotter for longer and so they are better to use if you have them.
You can also use stones or large rocks if you can't find any bricks. Just be careful as stones can crack when heated.
2. Wrap in Aluminum Foil
Wrap your bricks or stones in aluminum foil.
This stops the bricks from crumbling and making a mess in your cooler so they are easier to handle.
But the aluminum foil will also reflect heat back into the brick which means the brick will let off heat at a slower pace and thus stay hotter for longer.
3. Pre-Heat Over to 300ºF (150ºC)
Set the temperature of your over to 300ºF or 150ºC and give it some time to pre-heat.
You don't want to make your bricks too hot or you may damage your cooler or the food containers your food is kept in.
300ºF/150ºC seems to bee the sweet spot and is what most people recommend.
4. Place Bricks In Oven for 20-30 Minutes
Place your bricks in the oven side by side making sure to leave some gaps between bricks so the heat can get in on all sides.
Leave for 20-30 minutes so they brick completely warms up or you can leave for even longer if you want to.
5. Wrap Bricks In a Towel
Once you take your bricks out of the oven you'll want to wrap them in a towel.
This will protect both your cooler and your food containers for the extreme heat of the bricks.
Placing hot bricks straight into your cooler without a towel will likely melt the plastic and insulation and ruin your cooler.
6. Place In The Bottom Of Your Cooler (With Another Towel Underneath)
Place another folded towel in the bottom of your cooler. This will protect your cooler from the heat of the bricks so your cooler is less likely to break.
You can also use layers of cardboard if you prefer.
Then stack your hot bricks into the bottom of your cooler side-by-side. They should be wrapped in paper or a towel so they shouldn't be too hot for your food containers.
7. Place Food On Top
Now place your food directly on top of the bricks you have just put in your cooler.
You want your food containers to be close to the heat source so they stay hotter for longer.
8. Place a Towel or Cardboard Layer Over The Top
Once your hot bricks and hot food are in your cooler you'll want to put a final layer over the top of everything to stop the hot air from escaping.
You can use another folded towel or you can use a piece of cardboard cut to the size of your cooler.
Ideally you want little to no spare air space in your cooler so if you're cooler is significantly bigger than your hot bricks + food then use multiple towels to fill the space or used scrunched up paper.
This helps to trap in hot air and will keep your food hotter for longer. Click here for more tips on how to keep food hot in a cooler.
The More Bricks You Use The Longer It Will Stay Hot
The more bricks you add into your cooler the more total thermal mass there will be in your cooler.
Basically what the means is the more bricks you have the longer your cooler will stay hot and the longer your food will also stay hot.
Because there are more hot bricks there is more total heat energy and the cooler will trap most of that energy.
If you're finding your food is getting cold in your cooler too quickly then consider adding some bricks to the top of your cooler.
Alternatively you can also add hot water bottles with boiling water to the top of your cooler. I talk about this in my article on how to keep food hot on the go.
Be Careful Not To Melt Your Cooler
While coolers can be used to keep food hot and while hot bricks are a great way to do this it's important to note that coolers are made from plastic and aren't designed for extreme heat.
They are still mainly designed for the cold.
Coolers can't really handle direct contact with things above boiling temperature. In my article on can you put boiling water in a cooler I showed that coolers will warp and the insulation can melt when you put boiling water in your cooler.
Hot bricks are no different to this, especially if you're heating them up to 300ºF (150ºC) which is above boiling temperature.
This is why we wrap them in towels and place towels or cardboard down. It protects our cooler from the direct heat of the bricks and stops it from getting damaged.
Keep Your Food Out of The Danger Zone
It's always important to be careful when keeping food hot because if food is just warm and not hot it can be the perfect breeding ground for bacteria.
Between the temperatures of 40-140ºF (4-60ºC) is considered the “danger zone” for food where bacteria can easily grow. For some meats like chicken you'll actually want to keep it above 165ºF (74ºC) if you're storing it hot to ensure it doesn't spoil.
You'll want to keep your food out of the danger zone for as lot as possible by making it extra hot when you warm it up and by using hot bricks.
Once the food cools down and enters that danger zone temperature you'll want to eat it within about 1-2 hours to ensure it hasn't spoiled and isn't dangerous to eat.
Some food like rice are dangerous to keep warm even in a thermos as they are more prone to growing bacteria more quickly.
So be careful, keep your food out of the danger zone and use your hot bricks to keep your food hot for hours at a time.