Heatmax makes several different chemical warmers. Their Survival Heat pad is the largest warmer they make, touted to last up to 15 hours, be reusable (if resealed in plastic bag before it is depleted) and be environmentally nontoxic.
Holding Survival Heat up to the light reveals it is two smaller sized chemical heaters placed next to each other in a pouch.
The Heatmax pad is activated by exposing it to air and shaking it to combine the elements in the packets which then give off heat, the company says, for up to 15 hours. That’s a lot of heat and we were instantly skeptical. There’s writing on the packaging that says not to hold the Survival Heat pad directly against the skin – again we were dubious this type of warning would be necessary.
The test: We cranked one up with vigorous shaking for 3 minutes and then wrapped it in a 3 layers of a thin, $12, 50% wool blanket. It was left it outside for the night where we checked its temperature with a laser surface thermometer roughly every hour by unwrapping it. The results are charted below.
Heatmax says their product takes 15 – 30 minutes to reach maximum temperature and this is certainly true. For the first 15 minutes or so the heat it generated was lukewarm at best. With a little time, however, it performed like gangbusters. In our thin, 50% wool blanket it reached and stayed at temperaturesup to 144 degrees F for about an hour and stayed over 130 degrees F for a respectable 10 hours while being outside in the bitter cold. There was no other source of heat remotely near Survival Heat for any part of the experiment.
Did it last 15 hours? Almost. It generated a respectable amount of heat right up to about 14 hours, enough to help keep someone warm in an emergency situation. Of note, even wrapped in 3 layers of the wool blanket it did seem to get enough oxygen to function. We initially were concerned it would be O2 starved and not stay warm. It appears it would do fine in a sleeping bag though expsoing it to air when possible is recommended.
PROS: Works as advertised. Significant amounts of heat for a long time. Larger than most heating pads.
CONS: Pricey. Takes 15-20 minutes before it generates a useful amount of heat.
Overall we love this thing. It’s going in our survival kits.