Hi,
Just a shower thoughts I wanted to share.
I live in France (That's why how awful my English is), winter is cold. My flat is electric heated.
Electric heating is basically, transforming electricity in heat with close 100% efficiency (less some IR/electromagnetic).
From some point of view (data processing apart), a computer is nothing else than an electric heater.
Is the following idea somehow smart?: replacing heaters by mining bay, that turn in winter, getting (feedbacking with arduino) a constant overall 20°C ?
Would I have a substantial rake-bake ? (Like "pay the bay in a year or so" substantial)
(Though Ether mining seems more profitable, it's not the subject)
This is not a good idea. These ASIC devices are not meant to be turned on and off like your electrical resistance heaters to maintain your flat at 20 degrees; they tend to have very large current draws at power up so turning them on and off frequently could cause serious problems with the device itself or the power supply and there is a risk of fire. Black Arrow, KNCminer and Asicminer had issues with their devices catching fire under normal use. There are probably other companies that also had issues.
If you are set on mining, figure out a minimum power that would maintain your flat at a nominal temperature below 20 degrees when continuously running and use your normal heating to get to 20 degrees. There isn't a huge selection of miners to choose from though if you want a chance to "pay the bay". At least this way, your miner isn't powering on and off and you have no need for the arduino.
Looking at the price of the miners, I doubt this would be a way for your to lower your heating costs. Obviously you would need to give some data for anyone to make a proper calculation and since you haven't done that, I would take the advice here with a grain of salt. I wont mention names because their hearts are in the right place, it's just that they are somewhat fanatical about bitcoin mining. Oh hell, not even somewhat!