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Comment by jes5199 | Hacker News Reader

Sometimes electricity is essentially free. My home is heated by electricity (I live in California) - any watts that I spend mining bitcoins produces the same amount of heat as my electric heater, but has the advantageous side-effect of maybe making money.

(I don't actually do this because I don't have a desktop computer, and it's unclear if building one at this point will pay for itself before custom integrated circuits push the bitcoin difficulty so high that GPUs become worthless)

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Does your home have a heat pump? If so, your house heat pump is 3 to 4 times more efficient than the waste heat produced by your computer, and you are using 3 to 4 times more electricity compared to the same heat output from a heat pump.

Wait, Energy in = energy out. So what is the extra output that makes the computer so much less efficient? is it noise?

As the name implies, a heat pump moves heat around. When you heat your house with a heat pump, you're not (just) converting electricity into heat. The electricity is being used to move heat from outside your house into the house. You make the interior of the house warmer while making the exterior (very slightly) colder. It's exactly the same as an air conditioner or refrigerator, just pointed the other way.

Of course, energy has to be expended to move heat around, and there are inefficiencies. But with real-world equipment and common cold-but-not-too-cold temperatures, a single unit of electricity can be used to move several times as much heat as it would produce if you just converted it to heat directly.

A computer is as efficient as anything when it comes to converting electricity to heat. Heat pumps win because they're ultimately playing a different game.

No, I have radiant heat. I recognize that this isn't common in places that actually have weather.

When I lived in Santa Barbara we had a gas furnace. I'm surprised that, given the cost of electricity out there and the moderate temperatures which are nearly ideal for heat pump efficiency, that the financial incentive isn't there to convert even for moderate use.

But, thanks for clarifying.

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