Controlling ferment temps - two fermentors in the same fridge

[Tilt]

I've just done my first double brew day and both (Golden Strong, and a Belgian Stout) are chugging away nicely in the temp controlled ferm fridge.  

I'm using the same yeast (wy3522) and I'm looking for a similar fermentation profile for both beers - question is how do I do this when the temps between fermentors differ by 3 degrees.

One is sitting at 18degrees and the other at 21.  Which one should I tape the temp probe to and whats the best way of making sure the other one doesn't get too hot or cold?

[mattd2]

How are they set out in the fridge, one above the other? Might need to get a small fan in there to move the air round so the colder air doesn't "settle" on the bottom.

[Tilt]

Good point about the cool air settling low @ matt.  I've put the warmer one down the bottom with the probe insulated against it - and lightly wrapped the cooler one up top to help it retain some of its own fermentation generated heat.   

[Smiffy]

First thought, are your two readings taken with the same thermometer? Some of your difference could be from using different methods of measurement.

Second thought, to get the temperatures the same you need better conduction, not added insulation. If you are using plastic fermenters, I can see that being an issue.

I agree that the first thing to do is put the one which is currently warmer at the bottom, and that a fan will help create an even temperature around the fridge. Assuming that the cooling plate is on the upper part of the back, I would suggest the fan is at the front, blowing upwards, to work with the natural convection current coming down the back of the fridge.