I have never read the back of the heat pack bags thoroughly before. Today while packaging boxes I did. I did not realize the heatpacks can only raise temp 10-12 degrees within a cubic foot insulated box. You have to use multiple warmers to increase temp more than that. I typically do at least 2 anyway but this information makes it clear that I need to use at least 4 for shipping fish this time of year. I found this info really helpful and figured I would share. Also it states that the warmer will stop generating heat if the temp inside the shipping box falls below freeing which is interesting. Uniheat recommends usin double boxing with insulation an dheat packs between the double boxes.
heat packs- learn something new every day
- Thread starter msjinkzd
- Start date
that's why i am waiting to order more fish and shrimp from you.
weather here is like spring tho..weird el nino/la nina effects
weather here is like spring tho..weird el nino/la nina effects
Well, The packs and critters are still an exceptable temp when I get them in California. So you must be doing something right when you send them to me. 
My last 2 shipments over the past few weeks came from California to Florida and there was only 1 heat pack in the box and everything was fine.
I think something else that plays into it is where the package is physically; not something that you can easily control, even if overnight. Did it stay in a relatively warm sorting area/staging area..or already loaded out to a truck and then parked outside for driver pick up in the morning.
Hmm I have always only used one for shipping shrimp. But I usually let them sit for a few hours before tanking them ot the post office so they pre-heat.
INteresting, looks like shipping costs are going up some more!
INteresting, looks like shipping costs are going up some more!