Can you concentrate alcohol by evaporating the aqueous solution at room temp and collecting on a cold surface?
Yes you can do that, this technique is called 'distillation' (it requires a minimum difference of 10 degrees celsius to seperate two liquids with different boiling points, for efficiency), I don't know what temeperature the fish tank heater runs at, but you should know that ethanol i,e. what you are trying to separate evaporates at 37 degrees celsius same as normal body temperature, and the temperature of the cooling plate should be &lt; 27 degrees for efficiency

Edit -
yes, exactly the boiling point of ethanol is 78.3 degrees but ethanol is highly volatile and evaporates very fast at 37 degrees (without taking much water vapour with it) as far as my observation is concerned(with room temperature around, 1 atm pressure). the values I mentioned are the optimal conditions with experimental background. your goal as I can percieve is to avoid as much water as possible, if you take the condenser temperature to below 10 degrees the water vapour present in air will also start to condense at a good rate