Well  lets say  you use a space heater all year round.  I actually do know of a few office spaces that do.  As they have no control over the ac or the heat.

And they have too much ac in the summer

and they have too much heat in the winter.

I have 3  2gpu  card pc's mining in an office like this.  this pc's use 1080ti's and were purchased in 2017.

They do 330 watts each and are quiet to build something close right now I would need to spend  3600  which is equal to 2 of these units.

both use 1000 watts.  16th is about  $4.30 a day  since I would already use a space heater  that is all profit.

my gpus make about the same $4 a day.. So if you are a very specific user of space heaters the gear almost makes some sense.

4.30 a day x 900 days = 3870  just a little cheaper  and these would be okay for the right person.  A person that uses a space heater 24/7/365.