Only immersion thermal circulators specifically designed for cooking should be used for food prep.  This guide will explain which types are suitable for culinary applications.

Immersion thermal circulators such as the Polyscience 7306C are built with food grade stainless steel parts.   They should be used with distilled water, or chage the water frequently to prevent corrosion..  Circulators built for laboratory use are designed to be used with distilled/deionized water.  Of course this isn't always done, and many have corrosion on the immersible parts.  Another cause of corrosion is contamination with laboratory chemicals, or the wastes being analyzed. 

I am a chemist with 10+ years experience in process, environmental, and hazardous waste laboratories.  Over those years I have used immersion circulators in all of these settings.  I also ran a microbiological testing lab for a few years.  We used immersion circulators there also.  I currently test, and rebuild laboratory equipment for Lehman Scientific. 

There is no way to clean a used laboratory immersion circulator sufficiently, to be able to guarantee total decontamination.  Chemical residues will lodge in screw threads, between parts, in the pump blades, and even be bonded to the metal parts themselves.  I have even seen chemical residue inside the control box, probably from being in an over-filled bath.  These residues may leach into your bath and contaminate all they come in contact with, potentially contaminating your sous vide, or surfaces in your kitchen.  Also as in above, the parts in a laboratory immersion circulator will corrode if exposed to acidic conditions, or liquids containing salt. This will contaminate your bath,  with metals, some of which may be toxic.  Off flavors may even be introduced into your food.

Laboratory circulators may have the following names/part numbers.  These should never be used for food prep.

The most common are:

Model 70, labeled as Polyscience, Fisher Scientific, VWR, Cole-Parmer, etc.
Model 730, labeled as Polyscience, Fisher Scientific, VWR, Cole-Parmer, etc.
Model 2150, Fisher, Isotemp, Polystat, etc.
Any immersion circulator labeled as Fisher, VWR, Cole-Parmer, Daigger, Haake, Lauda, Thermo, etc.

At this time Polyscience is the only company I only know of that is making culinary  Thermal, or Immersion Circulators, along with baths, and their Anti-griddle cold cook-top.  Model 7306C is a food grade immersion circulator.

The model 7306C retails for $900+ which can be a lot of money to a start-up.  However scoring one of the laboratory ones on ebay for a hundred bucks or so is not a good deal as the unintended consequences of using one will be very costly.

If anyone has any question feel free to contact me.

Eric
a_caveman