Originally Posted by jacksonbrown
I have an analog temp controller. How would I be able to use that with the heater? I thought they could only be used for cold control.
What model do you own? Some can do both (one at a time) with a minor adjustment.
Another option would be a space heater with a built-in thermostat. I bought one at Lowes for about $25 last year. Then you don't need to worry about whether or not your model can work with a heater, and it could be used for something else.
For sizing, you could trace your carboys onto cardboard, and take those to the store for approximate sizing.