How MRE Heaters Work and How Should You 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 a 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. 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 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 bit of clear drinking 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 heaters 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, 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

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No matter which style of MRE heater you are relying on to warm up your ready to eat 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.

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 iron powder that would generate hydrogen gas as a byproduct. Hydrogen gas is, very infamously, extremely flammable 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.

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.

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