I had one of these back in the 80s and it seemed to work pretty good. While I was doing the reading for the posts on contact heating I ran across the naptha handwarmers again. Previously I’d used lighter fluid; the cost wouldn’t break me but since I carry Coleman fuel now I figured I’d give them another shot.
I ordered a Zippo 6hr model off Amazon as I heard the devices ran much longer than their 6hr/12hr names suggested. And the smaller one stands on a flat bottom for filling while the 12hr is curved.
It came in and I used the little filler to the 6hr mark (~10ml). Subsequently I use little 30ml squeeze bottles that hold 3 fills.
It runs for something like 10 hours, hot enough in the little bag that it’s uncomfortable through one shirt. Through a shirt and vest it’s perfect.
Lighting has been a bit of a PITA. Part of it is the inherent design, and part is the crappy catalyst used now - the old ones were platinum. Apparently they can be improved/rebuilt with actual platinum cats. See the Mountain Parameters YT channel for more info, staring with this one:
According to MP the Zippo is actually the most difficult to tune/use/upgrade, so people who want to tweak them might pick another brand. It looks like pretty much an cheap Chinese model will be fine for upgrading.
A gallon of CF is 378 fills at $0.026 (2.6 cents) per fill. Using 12oz lighter fuel bottles from the fuel cost would be about $0.37.
If we assume a cat head lasts for 50 sessions and costs $8 ($0.16/use), the overall cost per use with coleman is $0.19/use and with lighter fluid $0.53/use.
10hr HotHands and similar chemical products bought in bulk are about $0.59/use, so folks who don’t lug around a gallon of CF might consider that route instead.