I have attempted ut use MANY mre heaters but have only had like 5 of them work as intended. Most do nothing at all, some warm slightly. When they do work they work incredibly. Am I doin sowmthign wrong?
I raise the heater up above the 2 lines
slide the meal pouch into the pouch
hold the heater and meal above the lines
fill with water to between the 2 lines
let the bag
lay down on a horizontal surface allowing the heater to absorb the water until I feel it getting warm or 1 minute
fold the top of the bag over and shove the whole package into the meal the box came in with the open end facing slightly uphill.

most of the time they dont even get warm, sometimes they get a little warm, on rare occasions they get steaming hot.

how old are they?  all of my 5 year old ones are working

I like to put too much water in it, like 1/4" over the do not fill line.

And I don't lay it totally flat, it has to be at an angle...you need to put it on a "rock or something" so that the bag is at an angle.

they work most of the time for me...but I haven't had one in a while...

There are a number of lines on the bag.



"Between the two lines" can mean a lot of things.



The two lines they are talking about, are about maybe half an inch or less from the bottom of the bag.  The heater should be wet, but there shouldn't be much extra water.



My first time, I filled the bag about half way full, and it bubbled and still got hot enough... but... if you are filling it with lots of water it could keep it from getting warm like you describe.



The instructions should be a thick dashed line, and say "TO the dashed line" instead (then have no other dashed lines on the bag).



It also could be the bags were exposed to moisture and were already discharged over time.

The heaters I am currently using came out of sealed mre's late dark brown period so I believe 96ish. I am thinking that is why they don't always work really well. I do fill the water level to in between the 2 very obvious line that have text above them that say "fill to between lines, do not overfill". I do not leave it completely flat I just leave them flat until they start to get warm or 1 minute then prop them up on a rock or something so they are not sitting in the water (exactly how the directions say). I have re read the directions many times in detail to make sure I am not doing something wrong.

Are you saying the heaters don't get hot or that the meals don't get hot?  I have never had a problem with them (I am not .MIL, just use MREs every year for 2 weeks for hunting season) heating my meals up, but it is really a luke warm heat.  Never had a meal be steaming hot.  Better than nothing though.

I've got a bunch of these that until this spring I had no problems with them.

This spring, out of five, two worked well and one worked, but it took upwards of 15 minutes before it decided to get warm.

I only wonder if humidity had compromised them at some point in the past.

From now on, I plan to take twice as many heaters as I expect to use.  They don't weigh much.

If I'm in my car, I can always use my JetBoil to heat water to heat my MREs.

BTW, if you need a great heater to heat water quick, look into the JetBoil

I am saying most of them either don't get hot at all or the just get a little warmer than ambient temperature. I am pretty sure they are supposed to get MUCH hotter than this. I have had a couple of them over the years that get hot enough to burn you, they actually produce steam.

Well, I put 10 of them in a 2 liter coke bottle and filled it 3/4 full with water. I tossed it under my back proch steps for safety and when it went off, it blew my porch steps off.

Sounds like the heaters are to old.

A guy I used to shoot with told me a couple of years ago he bought a batch of just the heaters because for some reason the MREs he had came without them. He told me he had several out of the batch he bought that did not work.

My guess is that they were compromised in some way.

I have had the same kind of problem with hand warmers. I bought a box of them a few years ago for warming up guns at the range, and maybe 1/3 of them did not put out any heat at all, or very little.

I'll share a bit of Joe knowledge that may help.  

Overfilling is bad, the chemical reaction wont happen any quicker it just wont happen at all.
Put the MRE and heater into the cardboard box if you have it, fold the heater over so that it goes under the MRE
Keep it on an angle, if no rock is handy use your boot
If you need it a little warmer try adding a bit more water, sometimes the heaters have extra oomph left
knead the MRE before eating to disperse the hot food with the luke warm, it'll even out the temp
and lastly....MRE heaters either dont do anything really to warm your meal, or they work too well and burn the shit out of you.

most of us dont bother to use the heaters since it takes to much time and we usually field strip our MREs anyways to save space.  If you dont use them make sure you "use" them either by activating and then tossing in the trash or have other sorts of uses for them (warming your sleeping bag, heating the ground under your pad, or diversionary devices)

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Would been more fun with a spark. The gas released is Hydrogen if I remember correctly....

Well, it set all the car alarms off inthe neighborhood and a cop car did a slow drive by about 15 minutes later looking for the source of the explosion.

Never had an issue with one as long as I didn't overfill it with water

the ones I use get too hot to handle about 15 seconds after adding water



no problem getting food hot, even the side dish too



these are all newer, GI heaters

Beat me to it.  We used to tear up the MRE heaters, shove them in Gatorade bottles with a little water - shake - and toss them under people's cots.  Good fun.  I don't know about hydrogen gas.  The bottles would burst where the plastic started to melt from the heat.