Carboy Heating Pad or something else?

[glacious]

I am looking for a solution to keep my glass carboys a few degrees warmer (currently low 60's, need ~ 67 or so for my next couple batches).

I've made a system to control an outlet (RasPi, solid-state relay, thermometer in a thermowell), I just need to choose the heating element.

From what I've read, there are multiple options from brewbelt (too weak), fermwrap (looks a bit dangerous, and no auto-off), seed pads (bottom heat), water tub + fishtank heater (large and a bit messy, and household heating pads.

I am leaning towards a heating pad that I can wrap around my carboy, probably a 12" x 24" to cover 2/3 of it. Since this will be controlled by an automated outlet, the controller has to be a manual slide switch, not electronic (when you cut power to it, an electronic switch will not be 'On' when power is turned back on). An 'auto-off' feature is something most people on this topic try to avoid, but I would prefer it. The reason behind this is an added safety mechanism. These pads don't get too warm to really cause damage, and the digital controller should keep it in check constantly, however if something were to fault, the pad turning off after 2 hours is an added benefit. I would simply program the controller to have an 'off' cycle every 90 minutes where it just shuts off for 2 minutes.

So with that long-winded but hopefully detailed explanation, I am looking for anyone's experience with a heating pad that is 12"x24" or larger and preferably has auto-shutoff. The one I recently ordered from Amazon stated a 'slide control', but it appears they have updated to a digital controller (SunBeam king size with "ultraheat").

If I can't find one with auto-shutoff, this one looks like it will fit the bill:
http://www.amazon.com/dp/B000FGDDI0/?tag=skimlinks_replacement-20

If you have any other recommendations in this department that can be controlled with an automated outlet, please let me know as well.

Thanks!

 

[Beernik]

Any type of heater is dangerous with glass carboys. Uneven temperatures tend to create stress cracks and then the carboy shatters. If you want to use a belt or a fermwrap, rack it to a bucket.

 

[glacious]

Thanks for the reply Beernik. The heading pad (vs brewbelt or fermwrap) would provide a more gentle/event heat, especially when used with the pad or a towel. There shouldn't be any drastic or rapid change in temperature. This is certainly something to take into consideration, and can be programmed into the controller logic and put the heating pad on 'Low' to make it a slower heating cycle. I'm also not partial to brewing in plastic, especially heating plastic, but this is not a thread for that discussion.