Are fan heaters (almost) 100% efficient?
July 14, 2015 6:20 AM Subscribe
So, most electrical heaters are extremely close to 100% efficient in terms of converting electrical power into heat.
But is this true of fan heaters as well? In other words, how much energy goes into operating the fan as compared to the heating of the elements?
The reason why I ask is that my housemate is under the assumption that fan heaters, unlike other electrical heaters, are far less than 100% efficient. He claims that the energy required to operate the fan makes them incredibly inefficient compared to fanless electrical heaters.
I am skeptical. I would have thought that the cost of operating the fan is negligible (wikipedia seems to agree). However, I'd like some actual literature to show him, but have given up searching google as many of the top hits are companies selling heaters.
The reason why I ask is that my housemate is under the assumption that fan heaters, unlike other electrical heaters, are far less than 100% efficient. He claims that the energy required to operate the fan makes them incredibly inefficient compared to fanless electrical heaters.
I am skeptical. I would have thought that the cost of operating the fan is negligible (wikipedia seems to agree). However, I'd like some actual literature to show him, but have given up searching google as many of the top hits are companies selling heaters.
First response has it; I would just like to add two more things, one slightly pedantic and one extremely so. First, the fan motor has some inefficiency, which means the fan motor itself gets hot - so some of that 50-100 watts is going right to heat. Second, all of the stirring of the air eventually turns to heat - so in the end, all of the power coming in the cord turns to heat, in a technical sense. Whenever we talk about something being "inefficient", we're saying too much of the incoming power turns to heat; heaters are, near as makes no difference, always 100% efficient.
On the other hand, the moving air is going to generate a feeling of cooling so you might need more temperature to get the same comfort.
posted by ftm at 6:35 AM on July 14, 2015 [1 favorite]
On the other hand, the moving air is going to generate a feeling of cooling so you might need more temperature to get the same comfort.
posted by ftm at 6:35 AM on July 14, 2015 [1 favorite]
If you want to get into a real efficiency slap-fight, go for the system efficiency. If most of your electricity comes from thermal sources (coal, gas, biomass, nuclear) it's very inefficient to go from fuel → heat → electricity → transmission → heat. Every step has losses.
posted by scruss at 7:11 AM on July 14, 2015 [2 favorites]
posted by scruss at 7:11 AM on July 14, 2015 [2 favorites]
It is also something of a misnomer to say that electrical resistance heating is 100% efficient. It is certainly true that it does convert all of the electricity into heat, but the electricity was typically generated at a generating facility that was typically 30% efficient. Moreover, the key isn't efficiency in the conversion sense, but total energy consumption to heat a particular space. If a heater with a fan causes the room to reach the target temperature in 60 minutes, but one without requires 90 minutes, it is no consolation that the fan was 95% efficient where the radiant heat was 100% efficient. The question of concern is how much total energy was consumed to heat the entire space.
posted by Lame_username at 7:12 AM on July 14, 2015 [3 favorites]
posted by Lame_username at 7:12 AM on July 14, 2015 [3 favorites]
The reason why I ask is that my housemate is under the assumption that fan heaters, unlike other electrical heaters, are far less than 100% efficient. He claims that the energy required to operate the fan makes them incredibly inefficient compared to fanless electrical heaters.
This seems hard to compare, since they do different things. For example I have fan-based forced air run by a heat pump that at very low temperatures acts at 100% efficiency (ignoring air distribution). To heat the entire apartment without a fan you'd have to replace this with a lot of radiant baseboard heaters, I have no idea how to estimate what that would take or if it would even be possible, but it at least doesn't seem like it would be pretty.
Not only that, 100% efficiency isn't necessarily a good thing in at least three ways. First, it could be better: when not at very low temperatures a heat pump (basically an AC in reverse) can run at 200-300% efficiency, because it doesn't create heat, just move it around. Second, there's what Lame_username mentioned above. Third, it's not a useful measure of what the heating device does to the area it's trying to heat (sort of what my point in the first paragraph about fans was trying to get at also). There's some interesting info at this stackexchange questions. One choice quote: "That isn't a very useful way of thinking about efficiency, though, because any form of energy in your house will probably decay into heat energy pretty quickly. Your computer, television, and refrigerator are 100% efficient at heating your house from this point of view, because although they do things other than generate heat, the energy they use to do those things becomes heat in short order."
posted by advil at 7:26 AM on July 14, 2015 [1 favorite]
This seems hard to compare, since they do different things. For example I have fan-based forced air run by a heat pump that at very low temperatures acts at 100% efficiency (ignoring air distribution). To heat the entire apartment without a fan you'd have to replace this with a lot of radiant baseboard heaters, I have no idea how to estimate what that would take or if it would even be possible, but it at least doesn't seem like it would be pretty.
Not only that, 100% efficiency isn't necessarily a good thing in at least three ways. First, it could be better: when not at very low temperatures a heat pump (basically an AC in reverse) can run at 200-300% efficiency, because it doesn't create heat, just move it around. Second, there's what Lame_username mentioned above. Third, it's not a useful measure of what the heating device does to the area it's trying to heat (sort of what my point in the first paragraph about fans was trying to get at also). There's some interesting info at this stackexchange questions. One choice quote: "That isn't a very useful way of thinking about efficiency, though, because any form of energy in your house will probably decay into heat energy pretty quickly. Your computer, television, and refrigerator are 100% efficient at heating your house from this point of view, because although they do things other than generate heat, the energy they use to do those things becomes heat in short order."
posted by advil at 7:26 AM on July 14, 2015 [1 favorite]
With the possible exception of the power used to illuminate lights and with the energy lose from photons escaping out windows (IE: essentially nil) all power consumed by electric space heating eventually end up as heat in the living space. And therefor it is by definition a 100% efficient as a heating device.
Also even if you don't want to count the eventual heat that is produced by the fan as heating the fan's power draw is minor compared to the heating element. A typical 1500W forced air space heat will have a fan that draws less than 50Ws; probably much less. But even at 50 watts you are only losing 3% efficiency from the fan. So still 97% efficient.
But really 100% because the power used by the fan ends up as heat in short order.
posted by Mitheral at 11:21 AM on July 14, 2015
Also even if you don't want to count the eventual heat that is produced by the fan as heating the fan's power draw is minor compared to the heating element. A typical 1500W forced air space heat will have a fan that draws less than 50Ws; probably much less. But even at 50 watts you are only losing 3% efficiency from the fan. So still 97% efficient.
But really 100% because the power used by the fan ends up as heat in short order.
posted by Mitheral at 11:21 AM on July 14, 2015
If I were in a stubborn mood and wanted to be 'right' even in the face of the arguments above, I'd argue that a radiant heater directs more heat to the person, whereas a fan heater directs more heat to the room. From that perspective, heated clothing would be the most efficient.*
*Jacket nominal power is 100W, which is enough to keep you toasty on a motorcycle at 65 mph in 30-40 F weather when layered under normal riding gear.
posted by ryanrs at 6:32 PM on July 14, 2015
*Jacket nominal power is 100W, which is enough to keep you toasty on a motorcycle at 65 mph in 30-40 F weather when layered under normal riding gear.
posted by ryanrs at 6:32 PM on July 14, 2015
Oh, maybe you're not talking about personal space heaters? I which case I'd make handwavey arguments about heat lost in ducting running in less-insulated spaces, and air leakage from same. But energy losses from running the fan itself aren't a great argument.
[If you can't tell, I think all electric heaters are equally 100% efficient, which makes them inferior to gas heaters (no generator and transmission losses), or heat pumps (over 100% efficient), or even computers (you get to play video games while warming the room).]
posted by ryanrs at 6:41 PM on July 14, 2015
[If you can't tell, I think all electric heaters are equally 100% efficient, which makes them inferior to gas heaters (no generator and transmission losses), or heat pumps (over 100% efficient), or even computers (you get to play video games while warming the room).]
posted by ryanrs at 6:41 PM on July 14, 2015
Personally, efficiency is a bit of a mug's game; you should be looking at COP, EERs and Seers when talking efficiency.
An efficient reverse cycle air conditioner (aka heat pump for heating purposes) is hands down the most efficient - because it's stealing heat from the atmosphere, not generating it with electricity.
For your purposes, the piddly amount of power used by a fan (around an incandescent light bulbs worth) pales into insignificance when compared with the vast amounts of juice both (inefficient) heating methods require to do the job.
posted by smoke at 4:23 AM on July 15, 2015
An efficient reverse cycle air conditioner (aka heat pump for heating purposes) is hands down the most efficient - because it's stealing heat from the atmosphere, not generating it with electricity.
For your purposes, the piddly amount of power used by a fan (around an incandescent light bulbs worth) pales into insignificance when compared with the vast amounts of juice both (inefficient) heating methods require to do the job.
posted by smoke at 4:23 AM on July 15, 2015
This thread is closed to new comments.
Googling around a box fan seems to draw 50-100Watts, while a heater is 750-1500 watts. But heater fans are usually way less powerful than a box fan. So you are correct, the fan uses a small percentage of the power.
Plus you need to spread the heat around anyway, so you need a fan to move the air. Built in would be easier.
But i expect your housemate won't be swayed by logic, so good luck.
posted by TheAdamist at 6:29 AM on July 14, 2015