We were recently given a oil-filled heater at work because it was “More efficient” than the old one. The old one just blew hot air around. It looks like it has a bunch of coiled wires inside.
As I understand it, the biggest causes of inefficiency in electrical devices is energy lost to heat. When the device’s only aim is to make heat where’s the “wasted” energy going?
Conservation of energy says it’s got to go somewhere right?
I gather in this case, efficient means the amount it costs to produce a warm environment in the office. If the oil filled heater costs less and does the same work, than it would be more efficient than the electric coil heater.
There are three things that could make one heater “more efficient” than another. First, it might use a different energy source. Oil, coal, electricity, etc. are not all the same price, so a heater which uses a cheaper fuel will be “more efficient”, economically.
Second, many electric heaters are actually heat pumps, which effectively have over 100% efficiency. The extra energy comes from heat drawn from the surrounding environment (thus cooling the surroundings). The laws of thermodynamics say that you can’t do this for free, but the energy you “waste” in the process also ends up as heat, so it’s still a net win.
Third, some systems are more efficient at distributing heat than others. It doesn’t do much good to have a room where the area within two feet of the heater is too hot, while the rest of the room is still too cold. Better to distribute the heat uniformly, and better yet if you can manage to distribute it only to those parts of the room where the humans are.
A resistance-electric heater has a very high efficiency rating IIRC, there isn’t much that’s more efficient than that, especially as there’s no flue needed to remove hot combustion gases (like in a gas, oil, coal, wood, etc. heater). I’m guessing they must mean it’s cheaper overall, or more efficient from a “global” standpoint, as the efficiency of converting the oil to electricity and transmitting it to your heater (assuming it is oil; very little electricity is produced by oil, but I digress) is going to be around 25-35%. However, depending on where you draw your boundary condition, sometimes figuring out the true net global efficiency is quite involved.
Oh, wikipedia has an article on oil heaters. and electric heating. May provide some further incite.
Folks, the oil-filled heater *is * an electric heater. The OP question is: How can one type of heater that uses electricity in a closed room be more efficient than another type of heater that uses electricity in a closed room?
I don’t think it is really more efficient but it provides mor even heating. Those coil things are constantly cycling on and off and you’re either hot or cold. The oil acts like a thermal flywheel, allowing a more constant temperature. But none of this relates to efficiency as such.
Thanks CookingWithGas. Ironic username.
Yeah, it’s an oil**-filled** heater not oil-fired heater.
I think there is some confusion as what efficiency means. We appear to be merging the different ways we consider efficiency.
Economic efficiency takes into consideration the different costs of energy; Liquid Propane, Oil, Natural Gas and Electricity (coal etc). In this context we can consider a 96% efficient furnace (or even an 80% efficient furnace) to be more efficient than electric resistance heat because Natural Gas, relative to the cost of coal fired electricity, is cheaper to operate. This is still true although electric resistance heat may be near 100% efficient; meaning all the heat generated is delivered into the space. (as opposed to a portion going up a chimney)
Considering only operational efficiency (without regard to the costs of the various energy sources) electric resistance heat is more efficient than any fossil fuel furnace, including super efficient 96% models. (includes corn, oil, LP, NG etc) If the cost per Btu was the same for every energy source electric resistance heat would likely be the most efficient use of the energy source. (excepting heat pumps for a minute)
But the costs are different. Historically NG, LP and Oil were cheaper than electricity. Every couple years we put together a spread sheet and compare the cost of heating, using the metric “Cost per Million Btus.” ( and use real world costs from the local utilities) From a purely economic viewpoint Heat Pumps deliver a million Btus far cheaper than Electric, Gas, Oil or LP.
Oil filled heater, oh…yes, well…looks like I didn’t read very well, sorry. My fault. :o
Just to add, some forms of heat can be cheaper. If you are in a insulated or drafty spot a radiant heater will be better money wise as it will heat solid objects (including people) as opposed to convection which heats the air and that blows away.
Possibilities
Oil filled heaters, in addition to heating the air in the room, emit radiant heat. This can make the occupants comfortable at a lower ambiant temperature than a heater that puts out heated air.
I imagine that uniform distribution is a bad thing. The rate of heat loss depends on how hot things are at the periphery.
Does the oil-filled heater have a fan to move the heat around, or is it strictly radiant? If no fan, then that’s the efficiency increase.
Although it could be argued that the energy used by the fan motor is also heating the room, it’s not a selling point for the oil-filled heater manufacturers so why would they bring it up?
Edited title for clarity.
Colibri
General Questions Moderator
Well, if there are people at the periphery, you’re going to have to get that part of the room to the same temperature anyway. The question is just whether there’s an even hotter concentration somewhere.
Oh, and another factor is humidity. Adding moisture to the air will increase the heat in the room, without increasing the temperature. How comfortable humans are depends largely on the heat, but how quickly the heat is lost to the outside depends on the temperature.
I guess I should have been clearer over what exactly I was comparing.
Both heaters have been used on timers so they run from 8:30 till 17:30, so we don’t have to remember to switch them off.
The older electric blowing heater is about three foot tall and has two 100kw elements inside.
The oil-filled one is just a radiator, no blower. It’s a little taller and just over a foot across.
Though my question was more general than my two heaters. I was really wondering how two devices using the same power source at the same time, doing the same job, one could have different efficiencies.
Unless you actually compared the data plates on the two units to ensure their electrical consumption is the same, I’d bet that when they said “more efficient” what they really meant was “consumes less electricity & so costs less to operate” which means to you “puts out less heat and will leave us colder.”
I suppose one electrical heater could be operationally less efficient than another in a closed room if it had glowing coils that emitted some energy in the form of light which left a closed room through a closed glass window. I suspect this effect would be difficult to measure though.
But if all the energy consumed by the fan winds up as heat in the room anyway, wouldn’t it also be 100% efficient (as a heating device, not as an air moving device)?