The more I think about this the more I think there could be a real business model here. Make a device that looks and acts like a space heater but is in fact a miner loaded with your private keys. Market it as a "smart heater" that requires a wifi connection to operate. Sell it as a loss leader, or maybe even give it away for free. It doesn't have to be state-of-the-art hardware, so it can be cheap to make. Hmm...

Mining hardware is really expensive still, and they are constantly replaced by better models.

I have a massive surplus of solar in summer, and on my local auction sites some old miners became available. I considered picking them up and putting them to use using up my surplus "free" electricity.

I gave up when the mining ROI calculation came back with multiple years, even when you factor in a $0 electicity cost.

This might've worked 3-5 years ago (maybe more), but I don't see that happening now to be honest.

There are already such products, just search for "bitcoin heater" .

It's been done. Space heaters are like 200 bucks. Hard to compete with that.

Space heaters are $20* at Walmart for basically as much energy draw as a typical household socket can handle.