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Comment by minimaxir | Hacker News Reader

Conventional heaters are much more BTUs/watt efficient.

EDIT: By conventional I meant typical/normal, my fault for forgetting that conventional has a specific meaning.

Ah...you might want to ask a physicist or engineer about that.

Resistive heaters literally turn 100% of energy into heat—same as a computer. Unless it's a heat pump, it's impossible to get more efficient than that: the heat has to come from somewhere.

I seriously doubt this is true, though I also couldn't find any readily available sources that seem credible. The closest seems to be a DIY comparison by Puget Systems[1]. A computer drawing 1000W is losing some energy to light and sound, but the vast majority is heat.

[1] https://www.pugetsystems.com/labs/articles/gaming-pc-vs-spac...

Even light and sound become heat eventually.

I'm not sure what you mean by "conventional", certainly a plain resistive heater drawing 500W emits the same amount of energy as a computer drawing 500W. If you stretch the definition of efficiency, an infrared heater produces a similar subjective improvement to a room's temperature for less energy, as the infrared light skips heating the surrounding air and warms the subject directly. That is one downside to using computers as heaters - they produce almost no infrared, which can be less efficient for a given subjective experience.

Ah, but you shouldn't be using a plain resistive heater in most circumstances. Heat pumps are much more efficient.

I use a resistive heater. A heat pump would be about 1000 times noisier, and I live in an apartment, so I couldn't put the heat pump where I don't have to hear it.

No longer true since at least 5+ years. New heat pumps are very _very_ silent

Hate to be rude, but I doubt that anything with a compressor can be silent. All heat pumps have compressors, right?

I've been around dozens of air conditioners, every one quite noisy compared to a resistive heater. Are heat pumps quieter than air conditioners?

I have both a heat pump and resistive heating in my house. The compressor goes outside the house so you never hear it (and it's not particularly loud, just sounds like a quiet powerful fan). The indoor split units, as they're called, just blow air over the coils. The fans are very quiet, quieter than a typical standing fan or an A/C vent blowing air.

Resistive heating is usually much quieter, however it can make annoying ticking sounds as the metal expands against the wall, or an annoying electrical buzz as the power is cycled on and off, multiple times a minute. This happens even if they're installed perfectly, houses and walls move over time.

Just remember that an A/C is also a heat pump. Lots of apartments around the world with A/C.

There are lots of resistive heaters out there. In areas where it gets cold only one day a year, it's the preferred option. They are also used as "emergency heat" for heat pump systems, again for the 1 day a year it's below -17F or whatever. These are absolutely no more efficient than cranking out some renders on your GPU. If you plug a computer into electricity and it draws 1000W, the room gets 1000W of heat. If you plug a space heater into electricity and it draws 1000W, the room gets 1000W of heat. Computers cost thousands of dollars, a 1000W space heater costs $9.99.

To answer the OP's original question, the reason that resistive heating is used for space heating is because the heater itself is cheap. A GPU burning power to heat and do computational work is 100x more expensive for the heat output. If you have $1000 to spend on heating, you just get a heat pump or a real furnace.

The reason that people choose inefficient heaters is for the lower capital cost. Let's say that 1 day a year, you need heat. Getting 2kW of heat for 24 hours will cost $20 once to buy the heater, and $15 in electricity each time you use it for the 30 times over the 30 year life of your house, so you're spending $470. Meanwhile, if you wanted to be 3x more efficient and go with a heat pump in that room, you're paying at least $1000 for the heat pump and installation, but only $150 for the electricity. You come out behind even though you saved a ton of energy. Meanwhile if you're heating every day for 3 months in the winter, you wouldn't want to be anywhere near resistive heating, because the higher energy costs add up almost instantly.

TL;DR: the economics of resistive heating don't favor initial capital outlay that would be required to make them do useful computations while heating. People use resistive heating for "an emergency" and don't want to pay a lot of money for something they never use.

Even if capital costs weren't a factor, space heaters make a lot of sense in very common situations involving heating a particular area. It doesn't matter if heat pumps are 3-4x more efficient if one has to heat up 6x-8x the area instead of a small room that's currently being occupied (i.e. a home office).

Yup, very true. Something else I thought of is that if you are a landlord paying the capital costs, but your tenant pays the electricity bill, then you're incentivized to pick the cheapest heating system, not the most efficient one. This factor probably makes resistive heating more widespread than it should be.

I'm not sure I follow? How could they be much more efficient? They turn electricity into heat so pretty much 100% efficiency and a CPU turns electricity into heat and a small amount of computation occurs as a side effect. So all electricity into a computer becomes heat aside from a tiny fraction for the motion of fans etc which heaters also usually have.

Aren't all heaters 100% efficient?

Some amount of energy may be lost to the environment without heating up the intended space/object, although it is usually a relatively small amount.

Heat pumps are more efficient than that.

Ok, but they are moving heat, rather than generating it.

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