How efficient are space heaters?

Sun 22 Feb, 2009 09:45 pm
We live in an apartment heated by electric forced hot air. When we sit in the living room to watch TV, we like to use a small space heater just to warm things up a bit more right where we are, without jacking up the heat in the whole apartment. It occurred to me that this may be actually using more energy than just turning up the thermostat one or two degrees. Is there a formula for figuring out this kind of thing - in other words, which is cheaper, making the whole apartment (1620 sq. ft.) one degree warmer, or turning on a small space heater to, say, medium?
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Sun 22 Feb, 2009 09:52 pm
@Hannette Allen,
I think most of the modern small portable space heaters are pretty energy efficient and yes, it costs far less--as much as 10% to 20% less--to keep your thermostat cranked down for the parts of the house you aren't using and just heat the room where you're working, etc.
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Mon 23 Feb, 2009 06:29 am
throw blankets and thick socks work wonders too. Only cost about 5 bucks each one time..
Thu 26 Feb, 2009 10:29 pm
@Hannette Allen,
Look on the nameplate of the heater for the watt rating. If it's a 1000 watt heater, then for every hour you run it at full steam, it consumes 1 kilowatt hour of power. If you run it at "medium" you can assume that you're using 1/2 that amount per hour.

Multiply the number of hours it runs by the cost per kilowatt hour.

Electric heaters are 100 percent efficient. That means that there are no stack losses [chimneys] involved when you use electric heat.

Shewolf has a great idea too. A fleece throw or warm socks do a lot.
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Thu 26 Feb, 2009 11:56 pm
The question as asked was how efficient are space heaters, and the answer is that they are close to 100% efficient in converting electrical energy into heat energy.

As to whether it's cheaper to heat a larger area a smaller number of degrees or a smaller area a larger number of degrees there is no way to answer that directly without more data, however if the expected temperature rise is the same for both given areas, then heating the smaller area would have the higher efficacy (not efficiency) at producing the desired results for less overall energy costs.
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Hannette Allen
Fri 27 Feb, 2009 08:46 am
Thank you all for your replies. The problem with finding the cost per kilowatt hour for the space heater is that I still have no basis for comparison. My electric bill would show the kilowatt usage only for the entire month, and would include usage for lights, appliances, etc. as well as heat. And even for heat alone, it would be over a long period of time.

I guess my question should be: for a given hour of usage, which is cheaper: to crank up the apartment heat by one degree, or to turn on the space heater to medium? Even then, it would be hard to figure, as probably the cost of cranking up the apartment heat would depend on how cold it is outside, while the cost of using the space heater would remain constant.

As for wearing warm socks, etc., granted, but I still think that most people use some amount of energy-produced warmth in their homes; we are not living in icy igloos and wearing warm socks. The house does not have to be heated to greenhouse levels, but come on, guys!
Green Witch
Fri 27 Feb, 2009 09:25 am
@Hannette Allen,
Look for Energy Star labeling (I assume you are in the US) and that will help you determine cost of operation. I don't think it's big bucks if you are just looking to warm up a room for a couple of hours. I use a little space heater to toasty up the bathroom before taking a bath or shower. It has a automatic shut off switch to control the heat or if an object falls in front of it. It's costs less than a dollar per billing cycle.

What is warm to you? We keep our house at 62 during the day and 65 in the evening in deep winter. We let it drop to whatever at night. We can use our wood stove and crank the place up, but we prefer it on the cool side so it's not such a shock when we go outside. We also do the SheWolf method of adding an extra layer before messing with the heat. Also,my husband and I share a soft blanket on the couch when we watch a movie and that works great. If he's not available I recruit one of our dogs.
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Fri 27 Feb, 2009 10:59 am
@Hannette Allen,
The problem with finding the cost per kilowatt hour for the space heater is that I still have no basis for comparison.

To give you an idea of the cost, Hannette, all you'd have to do is keep track of the number of hours that you used or intend to use the heater. That's a simple calculation. As Chumly mentioned, it's not such a simple calculation to determine the difference between whole house heating, +1 or 2 degrees, compared to a lower house temp with space heating.

You're right to note that variable, outside temperature, for heat loss is affected by more than one thing.

It is likely that what you can do with a space heater is give yourself a more toasty feeling for less money that cranking up the entire system to get that same toasty feeling.

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Fri 27 Feb, 2009 11:03 am
We use heated blankets. It's pretty cold here most of the year, and with our high ceilings you could literally run the heater for hours and still be cold.

It's difficult to heat masses of air, takes tons of energy. Direct heat applied through an electric throw or blanket is far, far more efficient - not to mention pleasant!

Fri 27 Feb, 2009 12:18 pm
That's the beauty and effectiveness of radiant floor heating. It heats the surrounding objects, furniture, walls etc and the heating envelope stays within the range of the user instead of gathering near the ceiling as with forced air type heating. Sorta like an expanded kotatsu, for those who know that type of heating.

For a forced air situation open the windows and doors for a few minutes in cold weather and then close them and everything feels chilled. Do the same in a radiant floor heating [RFH] system and a few seconds after you close the windows/doors you feel heat radiating at you from the surroundings. The whole heating envelope returns to warm state very quickly, without a big blast from the furnace, as in forced air situations.

With RFH, you also don't get that dryed out feeling from having hot dry air poured over you.
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