I am re-posting the following after a suggestion from another thread on controlling paper development times in cool/cold darkrooms:
Here in the Midwest some of us LFers use electric pig warmer mats to keep print developing trays of the various chemicals at constant temperature (whenever the darkroom is colder than the 21C or 70F). There are no doubt many brands of such pig warmers, but those I've used successfully are made by
Kane Mfg., and at their webpage you can see these mats come in a variety of dimensions. Since they are designed for heavy-duty use in farrowing barns by hog raisers, they are totally unaffected by the water and other chemicals that we use in photo darkrooms, and to provide warming temperatures in an appropriate range for DR uses.
The thermostat controller I use is the ESAPCO Model TH-15-HM designed for Corrosive Environments, and
this link is to a distributor that sells on-line. It regulates the temperature of solutions in my enlarging trays to the desired 21C (or whatever one requires), and the whole system (mat and thermostat) is economical and very robust.
In my part of the Upper Midwest there is no concern about my basement becoming too warm in the summer, as the soil temperature about 3-4 feet below ground never gets above “cellar temperature” for wine storage which is 50-55F - so I use the pig warmer mat throughout the year.
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