Okay so mining pools are just adding lightning support which means that it makes sense to buy S9s pretty much forever because of how low payout thresholds will be with lightning withdrawals.

Electric heating tends to be more expensive than gas heating but a lot of people only have electric heaters. I don't have heat in my house so I use S9s in the winter to heat it. Some people even heat their houses with new miners, but it gets complicated versus just underclocking S9s and plugging them into 120v outlets.

But it costs the same amount of money to run a S9 as it does a 1300w space heater. Every watt consumed on a S9 produces the same amount of heat as a space heater. Even if you have a central electric heater, that heater will not work as hard as the S9 will offset the work needed to be performed by that central unit. That electric heater/space heater is not hashing and giving you sats though.