It takes about 6 blue ice squares.

Well I built an ice chest and put a computer fan in there hooked up to
a thermostat. The blue ice is on one side of a baffle, with the
fermenter and thermostat on the other side. The fan kicks on and pulls
cold air from the side with the blue ice when the temp drops below a
certain point. I need to change the blue ice about once every 3 days in
the summer. Here is a link to the plans:

[url]http://64.233.187.104/search?q=cache:Prp5nY-ZxVAJ:home.elp.rr.com/brewbeer/chiller/chiller.PDF+son+of+fermentation+chiller&hl=en[/url]

_Randal