thermal slow cooker

Thermos Thermal Slow Cooker Works Like An Insulated Crock Pot

Years ago I bought what you might call a Thermos thermal cooker. It’s Thermos brand, and we have used it many times to slow cook certain foods, kind of like an insulated crock pot would do… except you only heat it up once, and then insert into an insulated container to retain the heat.

Updated with newest (and less expensive) thermal slow cooker.
(jump below to recommendation)

Cooking requires fuel. And fuel consumption depends upon the efficiency of the cooker (and what you’re cooking, and how you’re cooking it).

Awhile ago I bought a small but well insulated thermos. I experimented while using it as a sort of thermal slow cooker for rice. Given the success that I had with it, I decided to go bigger.

So I purchased a purpose-designed thermal slow cooker. It’s bigger (4.5 Liters) and I have been very impressed with its ability to slow cook foods. It requires very little fuel compared to other traditional methods.

4.5L Thermos Brand
(view on amzn)
(UPDATE: see a less expensive Thermos slow cooker below)

How Thermal Slow Cooker Works

The principle of a thermal slow cooker is simple. It’s kind of like a crock pot thermos. Without having to plug it in.

A specifically designed thermal cooker will come in two sections. A stainless steel pot (with cover). And the insulated / double walled vacuum-sealed containment shell.

First, use the stove (heat source) to bring the pot to boil. For example water and rice, water and beans, sauces, stews, etc. Fill at least to 80% capacity for best thermal mass.

Next, remove the pot from heat. Put on the pot’s lid and set inside the the insulated thermal cooker shell. Close the lid to the the slow cooker.

Then, let it sit and do its job. The heat will hold for many hours.

It’s similar to how an ordinary crock-pot slow cooker works except without the electricity. In its place is a well insulated barrier to keep the existing heat ‘in’.

Why Use A Thermos Slow Cooker?

A thermal slow cooker may seem inconvenient (slow cooking) in a modern world of conveniences (plenty of fuel, electricity, microwave ovens, etc..). But with regards to preparedness (or simply saving fuel), it’s a great alternative method for certain types of cooking.

When I posted about “How To Cook Rice With 80 Percent Less Fuel” (article linked below), I was excited to take it to the next level. The 48-ounce wide mouth thermos worked well to slow cook a relatively small portion for one person. However if you’re looking to feed several people, this wasn’t going to be enough. This is why I bought a larger unit.

What I really like about it is the stainless steel pot. It is a standalone pot (with cover) which you sit on the stove (or a fire or whatever heat source is available). Once you’ve heated the ingredients to an initial boil, simply remove the pot from the burner and set it in the insulated thermal cooker. Close the lid, and you’re done. It’s just a matter of planning ahead for cooking your meal.

Recently Mrs.J used it to cook a pound of Garbanzo beans (for a tasty humus recipe) and I’ve captured a few photos:


As you can see, the temperature of the mixture was still 157-degrees even after 6 hours of slow cooking. Very impressive.

The ‘secret’ to a successful thermal cooker is its insulation. This particular Thermos brand apparently uses dual double-walled vacuum walls to keep in the heat.

( updated product: )

1.5L Thermos Brand
(view on amzn)

[ Read: Cooking Rice In A Thermos Saves 80% Fuel ]


  1. Ken, this looks great. Thanks for showing us the temp
    “still 157-degrees even after 6 hours of slow cooking”

    as that is something I’ve wondered about.

  2. I would love to know /love for you to try….

    could you hard boil eggs same way?

    1. Yes, we hard boil eggs by bringing to a boil on the stove, removing from heat and covering for 13 minutes.

      1. I also use a rice steamer for cooking eggs. 21 minutes to a perfect soft boil.

  3. This is one prep I will have to save for. When you consider the savings in propane I am sure it will pay for itself in short order. Even better if you will be stretching your propane in a SHTF scenario. Does anybody have the patience to figure out how long it would take to pay for itself?

    1. You can improve this. Use a stovetop pressure cooker, bring the contents to boil as quickly as possible. Cover the hissing vent with a small glass and put in into a self made haybox. Keep it there for a few hours and see the results.

  4. Glad to see the story on this Ken. As you know I’ve been a supporter of this system for a while. When we were in Mexico we were on small sailboat and had two of these cookers. While my wife was kayaking form our boat to another for a potluck she capsized and dumped one of the cookers. Now we have two of the pots and one of the cookers. Don’t ever immerse the cooker (insulated part) in water, it will fail. We have been using this system for around 30 years now and it is great. We have cooked chickens in this so don’t be afraid to try it with meats but for safeties sake use a meat thermometer as you experiment.

  5. Ken,
    I re read the article and cant find this answer,
    am wondering..

    how long can/have you leave something cooking in it? I see you show the temp after six hours, is six hours about as long as is good? (re concerns about food maybe going off, etc etc).

    I am wondering for someone who may be gone for 12 or 14 hours, if they could put the fixns for veggie chili in, and would it likely be cooled off by then, or would they come home to a hot meal?

    1. The only time you should be concerned about cooling temperatures over time is when you’ve added meat. When you drop below 145F for awhile, then concerns develop.

      If you’re cooking rice, beans, ‘veggie chili’, etc., then there are no concerns (no meat).

      I’ve not let ours sit for 12 hours or longer, but it would be a good experiment… The key for cooking a long time is to fill the pot (more mass to keep everything warm) and then bring to a boil. Also the longer it boils the less thermal cooking that’s required afterwards – although that sort of defeats the purpose of this cooker.

  6. Wow. I had no idea Thermos made this type of product. Thank you for the information.

  7. Okay, I’m not an expert on these but I do know a lot about them. I’ve owned 5 thermal cookers. The two I mentioned a couple of years ago and several replacements. Our 2nd thermal cooker was accidentally moved on the stove in it’s outer container to a warming burner that was on. It was ruined but the end result was two decent stainless pots were left.

    Tried to save a few bucks and bought a system from Saratoga Jacks, it had two inner pots neither of which worked as well as the Thermos brand, Next was a pot put out by Tayama. It too failed in it’s comparison to the Thermos.

    We sprung for another Thermos pot but a bit different than the one in Ken’s picture. The one we now have has side handles on the inner pot and the outer pot. It’s called a Shuttle Chef. As Ken’s picture shows both his inner and outer pots have bails as do our older pots. The good news for us is that our old pots work in the newer cooker but our new inner pot would not work in Ken’s. I saved a few bucks and wish I hadn’t. It’s a vastly superior pot compared to the Tayama and the Saratoga Jacks but not quiet as good as the one Ken has, almost but not quite. Search Amazon for RPC-4500 for Ken’s model

    This is case of where you get what you pay for. Don’t buy cheap. Amazon carries several cookers by Thermos. Perusing the site also showed a new one hat has two stacked 3 liter pots in a 6 liter container which looks interesting.

  8. Ken

    Do you have any taste comparisons for dishes cooked the old fashioned way versus the slow cooker? This certainly looks good but I am curious about how foods may compare cooked this way to standard stove top cooking. Thanks

  9. Around 1995-6 when we were building a cabin in the mountains on 3 day weekends, I bought a magicooker. It is the same principle. Only there is only 1 pot with a thermometer on the lid. After putting the food in and bringing the temp to the correct level you put it on a Styrofoam container with a lid. I left the styrofoam in the box it came in and just took the whole thing to the cabin. By dinner time we had a nice hot cooked dinner. Still have it but forget to use it. Way back before our time the pioneers used to make a meal in an iron pan or pot in the morning and just before they left to trek across the plains they would put the pot in a wood container filled with straw. They would cover it with more straw and come dinner, it was cooked and warm. They beat Thermos!

    1. Old lady:
      Is good to hear from you again, like me been a little quiet I guess.
      BTW New Mexico is a dreadful place so DONT move here…. right LOLOL

      1. NRP & Blue, I’m opposite you in the SE part of NM. We have a TP shortage down here & word is its your fault!
        Is our wonderful governor causing job losses in the oil patch there?
        As for NM being a dreadful place, good jobs are plentiful here, but you have to bring your own living quarters: man camps everywhere!

        1. Caliche Kid
          Re man camps

          Very reminiscent of pictures you see on Woodpile report from the early 1900s of migrant workers, only difference is now they are in Rvs,vans and campers,,,

        2. Caliche Kid;
          “Is 600 rolls really enough?”
          I hear the Oil Patch is absolutely going NUTS down that way.
          As far as the work here, yeah it’s dried up a lot, mainly work-over sort of stull. We actually lost over 9% of the population here do to ND and TX Oil Patch and the slow down here.
          As far as our communist governor…. I will not cuss on this BLOG, so as my papa taught me “if you cant say anything good about someone, than don’t honor them by even whispering their name”.

        3. NRP,

          Got a couple of young men, former neighbor kids here on the mountain, living in one of those man camps in SE New Mexico. Making more money than they ever dreamed of, working 80 hour weeks, living in a travel trailer.

  10. Here is an interesting piece of info i got from a recipe news letter i get.
    Kidney beans can be toxic if not cooked properly.
    A crock pot, or a thermal cooker like the ones at the top, do not heat the beans to a high enough temperature to render them safe to eat.
    Can cause vomiting and nausea as well as cramps,,,,
    This applies to the dry kidney beans, canned kidney beans are ok.

    1. the instructions for cooking beans ( and many other foods ) in a thermal cooker is to bring to the boil and boil for 10 mins, this ensures the whole contents of the thermal cooker are heated through and also meets the boiling recommendations for cooking beans .

  11. I have the two pot cooker made by a company that I don’t think is still in
    business.Does the name Bear Necessities ring a bell with anyone?
    It sure works great.Veggies in the bottom and meat on top.

    With a thermal cooker, a rocket stove, and Coleman stove top oven we could giterdone.

Comments are closed.