redneck temperature control chamber for fermentation

[RadicalCat]

I've been fermenting ales and lagers in the house, and I have rooms with good temperature ranges for those. But I haven't found a place warm enough regularly in the winter for DADY or the yellow label yeast I want to try out. So I set out to build a warming / temperature control chamber.

My first attempt was a failure. I got a large plastic pin, lined it with styrofoam insulation and spray-in insulation, with a hole for the chord of a space heater. After my first test run, I found the space heater kept kicking off. Probably not the best idea to begin with.

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Next I got two submersible, temperature adjusting aquarium heaters - one 125 watts, the other 100 watts. I've read a rule of thumb that 1 watt = 1 liter water. Tonight I'm testing both in a cooler in my outside shed, with a weighted bucket and thermometer inside. I'm optimistic that this setup will work, and that I'll only need one heater, hopefully letting me run two fermentation at a time. I expect some big temperature loss with the cracked lid, but I don't want to drill / insulate better until it looks like this concept will work.

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Any feedback, comments, or tips very welcome!