Today's interesting physics lesson, regarding the efficiency of heating with miners!

I recently listened to Bitcoin Audible Chat 79, with TheGuySwann and johnkvallis , talking about, among other things, using Bitcoin miners to provide heat. I have also heard another podcast episode, that I don't remember if it was on the same podcast or another one, discussing the efficiency of electric heaters vs. miners, not knowing the answer of it, or what's possible. I know the answer, so I thought I'd post an explanation, for everyone who is, or is planning to use the heat from miners to heat their home, their water, or anything else:

Energy can't be created or destroyed, only converted. Basic physics. And power is just energy / time, so the same thing goes there, unless we're talking about storage, in which case we would have to treat them differently, but since we aren't, we can say that all power put into something also needs to come out of it, and thereby continue talking about power instead: Efficiency is the difference between the power put into something, and the power that comes out in the desired form. The rest of the power thereby obviously comes out in an undesired form.

If the desired form is heat, we're in luck, because that's the kind of energy that is of "lowest quality", that every other kind of energy wants to go to eventually. There are scientific names for this, but I don't remember them, and they're not really important for this discussion.

So what kinds of energy, or power, do we have? In a regular electric heater, without a fan, we have electricity in, and heat out. Nothing else. I.e., the efficiency is 100%.

In an electric heater with a fan, we have electricity in, and heat, airflow and noise out. The airflow is a very small part of the power, and the noise is even smaller. Add to that, both are converted to heat due to friction in other parts of the room, except for what tiny amount of noise goes out through windows etc. and if there's some crack that some airflow can get out of - and in that case you have much bigger problems with heat escaping that way. So, the efficiency here is 99 point unknown number of 9s %.

So what do we have in a miner? We have electricity in, and heat, airflow and noise out, and a tiny bit of electricity out through the network cable, or maybe WiFi radio waves, if such miners exist. So except for a tiny bit of electricity or radio waves out, it's exactly the same as the heater with fan. The power of the network electricity or radio waves is probably between the noise and the airflow in magnitude, so we're still at a, maybe somewhat smaller, unknown number of 9s after the 99.

If we are comparing to something with a chimney or vent, such as gas, oil, coal, firewood or wood pellets, we have a more complicated system, where we have chemical energy left in the smoke/flue gas, from incomplete combustion, and heat in the wrong place - out the chimney - to think about too, so efficiency can be significantly lower than optimal, in some instances extremely low. But if we're comparing monetary benefits, we also have to take into account the difference in price per unit energy between your fuel of choice and the electricity.

But what about heat pumps? I just said electric heaters are 100%, but heat pumps are said to be more efficient than electric heaters? That would be true if you were only to count the electric power in - which we do, and call the resulting number COP, or Coefficient Of Performance - but in reality they have another power source: heat from the outdoor air, the ground, or a body of water, so the total efficiency is still <100%. Feel the air from the outdoor unit of an air heat pump, it is significantly colder than the surrounding outdoor air, when running in heating (the indoors) mode!

If the mining chips can handle the temperature that would be required (which I don't know what it would be), it would be interesting to try to build a miner-powered heat pump, with the same technology as a propane-powered caravan refrigerator, see en.wikipedia.org/wiki/Absorption_refrigeration , to at least get some extra heat this way in the winter, and some air-conditioning in the summer. It won't have as high COP as a regular compressor heat pump or AC, but those don't mine Bitcoin...