How MRE Heaters Work, and How To Use Them

Love them or hate them, MRE’s are a staple for military personnel, outdoor adventurers and the properly prepared prepper.

MREs contain everything that a hard-working body needs to survive and thrive, and it all comes in a compact, easy to carry and heavy duty package that will keep the food fresh and safe to eat.

These convenient meal options even include a way to heat up your dinner without a fire, a device known as a flameless ration heater, or FRH.

So how do MRE ration heaters work, and how do you use them?

Both varieties of U.S. ration heaters work by employing an exothermic chemical reaction, initiated by air or water, that results in a substantial amount of heat being generated. This heat byproduct is used to rapidly warm up a pouch of food to a palatable temperature.

I know quite a few folks who by custom or necessity consume MREs regularly and have never even bothered to mess around with the ration heater.

Despite stories you might hear about them, they work quite well, and are a convenient option for warming up your dinner when out in the field, no open flames needed. There is much more to learn about these ingenious gadgets so keep reading to find out.

How To Use the MRE Heater

Types of MRE Heaters

Generally speaking, you’ll encounter two kinds of flameless MRE heaters out in the world, so long as you are packing United States-sourced MRE’s, and military issue ones in particular.

Any military issued MREs produced prior to around 2010 all the way back to the mid 90’s will be a water-based MRE heater that requires a little water to activate.

Though reasonably effective, there are a few dangers associated with these heaters and they are a little slower than the newest variety. This generation of MRE heater functions by inserting the meal pouch into the heater, and then propping it up.

However, any U.S.-issue MREs and a few commercial varieties of MREs include the latest and greatest in ration heating technology that functions by reacting with the air itself, no water needed.

These heater pad types are used in tandem, and feature an adhesive that allows them to stick on to the meal pouch directly, quickly, thoroughly and evenly heating it from both sides.

Both work for MRE heating, both depend upon a simple chemical reaction and both are common enough in circulation that it is a good idea to become acquainted with each.

Using an MRE Heater Safely and Effectively

Disclosure: This post has links to 3rd party websites, so I may get a commission if you buy through those links. Survival Sullivan is a participant in the Amazon Services LLC Associates Program. As an Amazon Associate, I earn from qualifying purchases. See my full disclosure for more.

No matter which style of MRE heater you are relying on to warm up your ready to eat your MRE entrée dinner, they both work well enough and are simple and effective in operation.

Remember: if you are using the earlier variety of MRE heater, you will need a little bit of clean water to start the reaction and get your meal to warming.

You can find step by step instructions for both kinds below.

New Generation U.S. (Air-Reactive)

How air-activated MRE heaters work
  • Remove both ration heater pads from MRE. Inspect pads to determine which side contains adhesive coating covered by removable sticker. Opposite side is cover for air-reactive compound.
  • Remove MRE entree from box if required. Do not open entree pouch. Discard box if applicable.
  • Using caution, remove sticker from ration heater adhesive coating. Adhere ration heater to one side of entree pouch and repeat procedure with second ration heater on opposite side. Ensure that both ration heaters are firmly affixed to entree pouch.
  • Peel open exposed reactive element covers on each ration heater. Take care, as heaters will rapidly become hot.
  • Your entree should be thoroughly heated after approximately 5 minutes. Use caution when handling entree pouch and expended ration heaters.

Old Generation U.S. (Water-Reactive)

  • Remove entree box and ration heater from main MRE pouch. Do not destroy or discard box containing entree pouch as you will need it for the warming procedure.
  • Carefully open flap on ration heater and add clear, clean drinking water to indicated fill line. Take care that you do not overfill the ration heater.
  • Place entire entree pouch into ration heater packet before placing ration heater back inside entree box.
  • Use any convenient object to prop up entree box containing ration heater and entree so that water does not leak out of ration heater. Use a rock, metal object or something else that is not sensitive to heat.
  • Entree should be heated after approximately 10 minutes. Use caution, as steam will be emitted from ration heater during the heating procedure. Handle entree pouch and ration heater with caution.

No matter which type of ration heater you are using you will find the process simple, straightforward and more than capable of giving you a warm meal option without any campfire required.

Do These Heaters Really Produce a Hot Meal?

Like most items commonly used by members of the armed forces, there will probably be a proud history of bitching and griping associated with its use in field conditions. MRE’s, and the ration heaters that warm them, are no exception.

But despite their reputation among some troopers as being fussy, ineffective and not worth their weight the reality is that a ration heater, so long as it is not defective, is a generally reliable and convenient option for warming up chow when a campfire is not an option or just not practical.

However, it should be noted that the modern style of air reactive ration heaters are significantly better than the older water reactive style. Naturally, improved technology produces improved results.

The old, water reactive heaters could sometimes be finicky especially when improperly packaged or damaged in opening. Though they would warm up an entree a reasonable amount, there was often a trick to getting it to reliably heat up your meal piping hot.

The new generation, air reactive MRE heaters are much better in this regard, not only due to improved efficiency in the chemical reaction that makes them function but also because they directly contact and heat the entree pouch from both sides, ensuring a more even distribution of heat energy.

Bottom line is they both work and both are viable for quick and convenient warming of dinner in field conditions.

How Long Do MRE Heaters Last?

One of the most common questions concerning MREs themselves is how long they last. The answer, of course, is that it depends, and depends upon many factors. However, not too many people care to ask how long the heaters will last, assuming that they simply last as long as the MRE itself will.

This may, or may not be the case. Generally speaking, any flameless MRE heater should last for at least 5 years assuming that the packaging of the MRE and the wrapper of the heater is not compromised.

If the former is punctured or torn, the heater will degrade more quickly, and if the wrapper of the heater itself is damaged chances are it will be no good whenever you pull the MRE out to eat it.

That being said, there are plenty of instances where I personally have cracked open a 10-year-old MRE and used the heater with no problems. It did not get my entree as hot as I would have preferred it, but it definitely worked.

Assume that so long as the MREs are stored in mild, proper conditions and not damaged that the heaters should remain functional for as long as you are willing to risk eating the MRE!

Can You Store MRE Heaters Separate from an MRE?

Something else to consider is that plenty of people break down their MREs in order to itemize individual components or to reduce the overall footprint of their food.

This is certainly a viable technique, and I do the same thing as a rule with MREs that I know I’ll be eating in the near future.

But once again, little attention seems to be paid to the heater. I know many people simply throw the things out, but I hope after reading this article you might have a different point of view about them.

So the question now is whether or not you can store the MRE heater separately and safely after removing it from the main MRE pouch.

The answer is yes, generally. Again, you should expect a slight reduction in shelf life whenever you remove the components from the heavy pouch that contains the MRE.

But, assuming you are careful and do not damage the wrapper of either a water or air activated ration heater, should be able to keep them safely and reliably for a time.

If I were you, I would try to use them within a year or two, at the most.

Safety Considerations

As you might have already guessed, any device relying on a chemical reaction energetic enough to heat your dinner might entail a few safety hazards if used carelessly or by an ignorant operator.

These MRE heaters are no exception with the older, water-reactive style in particular having a few special drawbacks that might make them unsuitable for certain environments.

Namely, these older style MRE heaters relied on a chemical reaction incorporating magnesium metal and iron powder that would generate flammable gasses- hydrogen!- as a byproduct.

Hydrogen gas is, very infamously, extremely combustible and if used in an enclosed space could produce a legitimate explosion hazard.

Notably, these older MRE’s and their heaters were not allowed on submarines, aircraft or in most sensitive installations for that very reason. The new generation MRE heaters do not have this particular quirk.

Also, new and old generation MRE heaters alike both get quite hot when functioning, and are capable of burning exposed skin. The older generation heaters once again pose a more particular hazard because they generate copious amounts of steam that could produce burns if handled carelessly.

They can easily push water alone to the boiling point, so you could be in bad shape if you don’t give them the respect they deserve.

The design of the new heaters greatly increases efficiency in heating the meal and keeps the exterior of the unit itself much cooler, reducing risk.

Once again, either will do the job and both are safe so long as you are reasonably cautious, and if you are forced to rely upon the older style MRE heaters and sure that you allow for adequate ventilation if operating them in an enclosed space.


MRE heaters are simple but ingenious devices that rely on an oxidizing chemical reaction to generate a significant amount of heat that is then used to warm an entree pouch.

Whether you are relying on a newer or older generation MRE heater, they can generally be depended upon to produce warm dinner in field conditions without any benefit of a campfire. MRE heaters are a generally safe and definitely convenient option for those living or working in austere conditions.

Leave a Comment

Your email address will not be published. Required fields are marked *