We have used the 60-hour packs from http://rldtheheatsource.com/ for several years, and are quite pleased with them, although trusting any heat pack for the full 60 hours is foolish. Personally, I try to ship stuff so it is delivered within 48 hours, just to be safe.
I don't understand how they could stop functioning below freezing, and suspect it is a misinterpretation of observation. These heat packs typically work by a simple, exothermic, chemical reaction - the oxidation of iron powder upon exposure to moisture (humidity) and oxygen - which begins once you open the air-tight bag. That process is not overly temperature-dependent, especially if you've started it at room temperature, so are already warm. Instead, I'd bet the chemical reaction is slowed by either a lack of moisture or a lack of oxygen. The simple fact is that folks typically seal their shipping boxes up tight to contain the heat, not realizing the heat pack will consume the oxygen faster than it can be replaced, so the process slows and little- to no heat is released. If the box is not totally sealed (I often poke holes in it), it usually woks fine. In the middle of the dead of the dry winter though, I'll sometimes stick a sopping paper towel inside of a perforated baggie in the box to ensure a source of humidity. Ray Barkalow - First Rays Orchids - www.firstrays.com Plants, Supplies. Books, Artwork, and lots of Free Info! ----- Original Message ----- From: "Redman, Julia C." <[EMAIL PROTECTED]> To: <[email protected]> Sent: Sunday, December 23, 2007 11:11 AM Subject: [OGD] Heat packs - shipping supply question Hi folks, Where do those of you that ship plants in winter get 60hr heat packs? What brands are best? I only found one brand called uniheat, and the review I read states that they stop working below the freezing point. This seems rather counter productive. I will appreciate any information you can provide. Thanks, Julia -------------------------------------------------------------------------------- > _______________________________________________ > the OrchidGuide Digest (OGD) > [email protected] > http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com > _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
