More efficient electric heat for the shop

[Dan Friedrichs]

Rich,

Then explain to me: if I put, say 10kWh into each of those three heating elements, and the elements are in a sealed and insulated room, where does the energy go, if it doesn't get turned into heat? It has to go somewhere - it cannot disappear.

What you're talking about it designing heating elements that radiate different wavelengths of IR radiation (heat), which will then heat different materials at different rates. However, any heater will always put out 100% of it's input energy as heat (and some negligible amount of EM radiation) - if it doesn't, it violates the law of conservation of energy!

[Rich Lightfoot]

A. The base assumption that an electric heater generates nothing other than what we can perceive as heat is wrong. Does it radiate energy? Absolutely. Is all of that energy harnessed as heat? Absolutely not.

B. Where does the energy go? Who said it had to go anywhere? The energy can be stored in whatever materials will hold it but this does not automatically translate to heat. Indeed with the right materials you could collect some of the radiated energy, convert it back to electricity and store it in a battery with minimal actual heat involved.

As the OP mentioned, one of the heaters was an oil filled unit. In this example electricity is applied to a heating element with the full output of the element being stored in the oil which in turn allegedly radiates more of the energy in the form of heat than the element alone would creating an increase in efficiency.

Finally, just because the walls of a room are solid to us does not mean they are impermeable to radiated energy.

C. My main point here is that not all electric heaters are created equal, if they were we wouldn't have so many different types. Since the OP was discussing the efficiency of heating a room, take it in that vein. Let's say I have to build a dog house and I don't want my dog to freeze so I decide to heat it. For whatever reason my only 2 choices to heat the dog house are a 30 watt soldering iron or a 30 watt incandescent light bulb. In this case the light bulb is clearly the more efficient choice for heating and it's not even technically a heater.

[Dan Friedrichs]

A. The base assumption that an electric heater generates nothing other than what we can perceive as heat is wrong. Does it radiate energy? Absolutely. Is all of that energy harnessed as heat? Absolutely not.

Ehh - I don't buy that. Sure, it will generate a negligible amount of EM radiation that escapes the immediate area, but what else? I'd say 99.9999% of that input energy ends up as heat within the immediate vicinity of the heater. Better insulation could catch 100% of the output.

B. Where does the energy go? Who said it had to go anywhere? The energy can be stored in whatever materials will hold it but this does not automatically translate to heat. Indeed with the right materials you could collect some of the radiated energy, convert it back to electricity and store it in a battery with minimal actual heat involved.

In what form is it being stored? If you heat something, you store energy in it. You could create a chemical electron gradient (battery), but I'm not familiar how to charge a battery directly using any heater output (you could connect a thermoelectric device or a thermocouple to a battery charger, but the energy gets turned into heat first, then electricity). You could store kinetic energy in a spinning flywheel or something, but again, I'm not sure there's a easy way to make a flywheel spin using an electric heater.

As the OP mentioned, one of the heaters was an oil filled unit. In this example electricity is applied to a heating element with the full output of the element being stored in the oil which in turn allegedly radiates more of the energy in the form of heat than the element alone would creating an increase in efficiency.

If the element were alone and using the same amount of energy as the element in the oil, you're suggesting that it would radiate less of the energy it consumes as heat? Explain to me where the difference comes from - where does the "rest" of the energy go, then?

Finally, just because the walls of a room are solid to us does not mean they are impermeable to radiated energy.

No, but again, EM radiation from an electric heating element is negligible. IR and visible are nearly entirely absorbed by the walls (where they turn into heat). I think it's reasonable to assume the thing isn't giving off any X-rays or cosmic rays.

C. My main point here is that not all electric heaters are created equal, if they were we wouldn't have so many different types.

Different heaters are useful in different situations (long term heating of a room vs. just getting the bathroom warm very quickly while I'm showering). That doesn't mean some are more efficient than others.

Since the OP was discussing the efficiency of heating a room, take it in that vein. Let's say I have to build a dog house and I don't want my dog to freeze so I decide to heat it. For whatever reason my only 2 choices to heat the dog house are a 30 watt soldering iron or a 30 watt incandescent light bulb. In this case the light bulb is clearly the more efficient choice for heating and it's not even technically a heater.

It is not more efficient - you're putting 30W of power into it and getting 30W of heat energy out either way, so the efficiency of both is 100%! (since incandescent bulbs are only around 1% efficient light sources, I'm just rounding it up to 100% Besides, the 1% of light energy leaves the bulbs as photons, strikes the walls of the dog house, strikes electrons and increases their kinetic energy, which is heat - thus, even the light energy becomes heat)

I agree that the bulb may be more effective at heating the dog house, though, simply because of the way it's designed. The vacuum between the hot filament and the bulb means all the energy is being transmitted through radiation, which distributes around the dog house more easily than the purely conducted and convected heat from the soldering iron. However, if your dog house is well-insulated (meaning no energy is leaving), and if both the bulb and the iron are drawing the same power, the total heat in the dog house will increase exactly the same amount using either one. If you don't believe that's true, you're suggesting that either 1) energy is leaving some other way (which I said we would assume it wouldn't due to good insulation), or 2) energy is disappearing, which is physically impossible.

Sorry that this has degenerated into a overtechnical discussion of physics My point to the OP, though, is that you can't make a sweeping statement like "Oil filled heaters are more efficient than ceramic cube ones" because:
1) It's not true from a technical perspective: If we define the efficiency of a device as the magnitude of the desired output power over the input power, any electric heater is 100% efficient.

2) If you're discussing trying to save money by reducing heat usage (like the OP was), choosing a different heater is not fruitful - since any heater generates the same amount of heat per unit energy input, the correct thing to explore is better insulating the area you're trying to heat.

[Sonny Edmonds]

Not only that, but it's still going to cost you$3 for a cup of coffee at Starbucks.
If you drink it fast, you won't loose as much of the heat into your hands as you could put in your tummy.

[Charles Seehuetter Panama City]

Ehh -
Sorry that this has degenerated into a overtechnical discussion of physics My point to the OP, though, is that you can't make a sweeping statement like "Oil filled heaters are more efficient than ceramic cube ones" because:
1) It's not true from a technical perspective: If we define the efficiency of a device as the magnitude of the desired output power over the input power, any electric heater is 100% efficient.

2) If you're discussing trying to save money by reducing heat usage (like the OP was), choosing a different heater is not fruitful - since any heater generates the same amount of heat per unit energy input, the correct thing to explore is better insulating the area you're trying to heat.

Okay but from a non-technical perspective, bottom line is that my electric bill averages $30 to $40 a month lower since the new heat pump was installed compared to the past two years with the old heat pump. Same size, same thermostat settings, same insulation, same house, same ducting, same filters and same comfort level. I guess what I'm trying to say is that if I see that my electric bill is lower using one heater over another then I'm going to use the one which I perceive to be using less energy to produce the desired effect.

Chuck