Updated on 12.08.11

Saving Pennies or Dollars? Space Heaters

Trent Hamm

saving pennies or dollarsSaving Pennies or Dollars is a new semi-regular series on The Simple Dollar, inspired by a great discussion on The Simple Dollar’s Facebook page concerning frugal tactics that might not really save that much money. I’m going to take some of the scenarios described by the readers there and try to break down the numbers to see if the savings is really worth the time invested.

Shaun writes in: This time of year (late fall, early winter), the local hardware stores offer several varieties of space heaters. Is it possible to realize meaningful savings by using one or more space heaters to locally heat parts of your house while keeping the thermostat at a very low setting?

This is absolutely a great way to save money in the winter for the reasons you describe. If you have a space heater and run it in only a room or two, then keep the thermostat in your home quite low, you’ll save a ton on your energy bill.

For example, in my own home, we use this 1,500 watt space heater.

Most of the time during the winter, particularly on weekends, we let the whole house stay cool and keep only the family room warm. When we switch to this mode, we turn the thermostat down to about 45 degrees, which is cool enough that the furnace virtually never turns on.

Then, we all settle into the family room. When we notice it getting cold, I’ll flip on that space heater full blast for a while, using 1,500 watts for about ten minutes until the room is warm. Then I’ll turn it on really low, where it uses about 200 watts, and this – plus our body heat – keeps the room we’re in pretty warm.

So, let’s compare that for a 24 hour day against the use of our furnace.

With normal furnace usage, we’ll leave the house set at about 60 degrees Fahrenheit. We wear long sleeves and pants during the winter, so this feels fine. We have an approximately 25 kW furnace (based on the information I could find on the labeling, which is appropriate for a house of our size in a cold climate), which flips on for about ten minutes per hour, on average (I’ve measured it on cold winter days).

Thus, over the course of a full day, our furnace will run for four hours. With a 25 kW furnace, that’s 100 kWh of usage, or about $12 in energy use.

With a space heater, over that same period, I would run it at 1,500 watts for about 10 minutes, then at 300 watts permanently afterwards. That totals approximately 75 kWh of usage, or about $9 in energy use.

In other words, if we are going to spend most of the day in the family room, we’ll save dollars by turning the furnace very low and just heating the family room with a space heater. (At the end of the day, we’ll often go upstairs and position the space heater between the bedrooms at a fairly low rate and it keeps us quite warm during the night while the rest of the house is cool.)

For us, that savings is about $3 a day, according to my math.

However, the variables for your situation are large. How big is your house? How cold is your climate (generally, furnaces in colder winter climates tend to have higher wattages)?

Perhaps most importantly, how much of a difference is there between the area you want to heat via space heater and the area you want to heat via furnace? If you’re living in a small apartment, for example, or have a house that’s less than 800 square feet or so, you’re probably not saving much at all with a space heater.

The savings kick in if you have a large house and are only heating one room with a space heater and if you live in a climate with a large difference between indoor and outdoor temperature.

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  1. Michelle says:

    I think what is missing from this post is comparing different ways people heat their homes. Where I live, when someone talks about having a furnace, it means they use natural gas to power the furnace and heat the home. This means that there is one thermostat for the whole house. My own home is electrically heated, so there is a thermostat in each room which controls a baseboard radiator.

    I can keep the temperature very low or off in every room except my living room (where I spent most of my time) and heat it electrically. So what is the difference between using that one electric baseboard radiator in the one room and using one space heater which also uses electricity in that room?

  2. Baley says:

    I can’t imagine hanging out all day in a 60 degree house! Wow. Anyway, we have an electric heat/AC unit that heats our small (1100 sq feet) apartment AND the one below us (used to be all one unit, split into two but we share a thermostat and the heat/air unit). It’s always colder downstairs, but I think the tenant uses space heaters or just lots of blankets, and we have control of the thermostat (the downstairs tenant is the landlord’s daughter so we’re the ones paying rent and therefore have the privileges). Anyway, that’s a bit off topic except to explain that basically our heat has to run nearly constantly to stay up to a comfortable temp (71 for me). I could probably turn it down some, but then our baby would get cold in her room (which is for whatever reason a little colder than the rest of the house). Would it save money to put a space heater in her room and drop the overall temp down a couple of degrees? On the other hand, I would feel bad about making it even colder for our downstairs neighbor. Oh, and we have old, single pane windows that are very drafty. Any tips on fixing that for cheap (since we don’t own the place)? Our electric bill is a little out of hand (we split that with our landlord, too).

  3. Johanna says:

    I’m confused. Is your “furnace” an electric heater? Or does “energy” happen to cost exactly the same in your area, regardless of whether it’s electricity, natural gas, or whatever?

  4. Jason says:

    I think the premise here is valid and worth adopting. I do have one concern, at that’s the (admittedly remote) danger of keeping a thermostat at 45 degrees.

    Where I live–northern Iowa–it gets pretty cold. If the power were to go out, I fear that the already-minimally-heated areas of my house could approach freezing in a short period of time–like overnight. When it gets to -10F or below, the pipes in that part of the house might freeze and burst.

    I guess all I’m saying is that a starting temp of 45F is just a short power-outage away from troubles that make $3 seem fairly trivial. A higher starting temp would offer a greater window of safety in that regard.

    Other than that, yeah, space heaters are great and we use them all the time.

  5. Riki says:

    I’m also confused.

    Your calculation for the cost to run your furnace makes no sense. Are you folding the cost of fuel (oil, gas) into the calculation without showing us? Or are you basing it on the cost of electricity? Rest assured, the cost to run MY furnace comes from the cost of the oil, not electricity.

    Also – 60 degrees is pretty chilly for my liking. Even with long sleeves and slippers.

  6. Riki says:

    Nope, Trent, you used the same cost per KWh of energy for both the space heater and the furnace. Do you have electric heat in your home? If not, your calculation is entirely inaccurate.

  7. Johanna says:

    Apparently there is such a thing as an electric furnace (I did not know that). So now I’m less confused. If you’re heating your whole house electrically, then you probably do save money by heating just one room versus heating the whole house.

    But if you heat your house with gas (or oil or some other fuel), that usually costs a lot less than electric heat, so it’s likely to cost less to heat the whole house with the furnace than to heat just one room with an electric space heater.

  8. josh says:

    @#1 Michelle

    Furnace = forced hot air
    Boiler = forced hot water

    The source of fuel can natural gas, LP, or oil. Someone who has electric heat will typically be radiant heat.

    There is really no savings that comes with a space heater in your situation. Essentially, you already have hard-wired space heaters in each room. In extremely cold climates this is a VERY inefficient heating system.

  9. Andrew says:

    Not to sound like a finger-wagging scold, but using a space heater can be dangerous if you don’t follow a few elementary precautions–don’t leave it on unattended, don’t place it too near curtains, don’t let it get knocked over by children or pets, etc.

  10. lurker carl says:

    Perhaps Trent does not know what kind of fuel their furnace uses or the cost per therm.

    So it takes $9 per day to heat one room with an electric heater versus $12 to heat the entire house with the furnace? I hate ice cold beds and bathrooms, we’ll spend the extra $3 for comfort. I’d be worried about leaving a space heater running unattended all night, particularly with three small children in the house. If I recall, Trent gets sick with horrible colds every winter – there may be a connection here.

  11. Adam P says:

    Unrelated to this post, Johanna and lurkercarl and other regulars, JD posted my question today on reader of the day today at GRS and I’d love your inputs and some of the regular snarkers too.

    Related, space heaters use a lot of electricity. I have one of those electric fireplaces for a mantle and a center in my condo living room, and if I use it and my plasma tv (same fuse) it will trip a breaker. Furnace it is.

  12. Riki says:

    This is my first winter owning a home (and paying for oil!) so I’m figuring things out as I go along.

    Currently we have the thermostat set for 68 degress while we’re at home and then down to 64 degrees during the night. I’m not sure if that’s reasonable or not but I’m definitely finding the house chilly. My office (where I spend a ton of time) happens to be quite coolso I have asked for a space heater for Christmas and that should help.

    This topic is very near and dear to my heart. When we first purchased our home, it had a 60 year old furnace that turned out to be woefully inefficient. We burned an entire tank of oil during the summer just to keep our hot water hot. Not good. So, we broke into the ol’ emergency fun and had an incredibly efficient cold-start boiler installed. It was expensive but my calculations indicate it will pay for itself in less than 5 years. And I really appreciate the environmental benefits of burning less oil as although we were interested in non-oil based systems none of the alternatives were affordable or workable in our current situation.

  13. valleycat1 says:

    Trent could save even more if they just start the space heater on low before the room gets cold, instead of having to run it full blast after they feel the cold. And, I’m assuming they later heat the rest of the house (since he says he turns it down in the morning on the weekends), so it seems to me it would even out after having the furnace run full bore long enough to get the temp back up to 60 or so from 45.

    I have relatives in Iowa & upper New York state & they all keep their houses much cooler in the winter than we do in the south & west.

  14. Jonathan says:

    @Baley (#2) – We keep our house around 60 degrees in the winter as well. It takes a bit of time to adjust, but now it is quiet comfortable. We do have to turn up the heat when we have guests, however, since it does seem very cold to many people.

  15. Cathleen says:

    I live in the Bay Area, in a house built in the 1920s, and I’ve never turned on the central floor heat unit and I’ve lived here for 20 years.
    My husband thinks I have a body temperature problem!
    Our PGE bill is about $75 a month for gas/electricity.
    (he wears sweatshirts when he’s cold :)

    I cannot imagine living in a house with a temperature of 68 degrees, I’d melt :)

  16. Noel says:

    With the use of electric heating system installed in our apt, we ended up with a bill of $450 in peak winter (for 750 sq ft NY apt) last year. We bought Kenwood Oil heater from Home Depot ($65)later last winter.
    I noticed, use of space heater is expensive. I used Kill-A-Watt to figure this out, so I am super confused with Trent’s calculations. I admit that I don’t know how much electricity our heating elements use but comparing space heater and oil heater, space heaters are expensive.

    With oil heaters, you can let them run the whole day and still it costs less. Only disadvantage is, it will not give you a blow of hot air at instance, but you won’t need it if you are using oil heater whole day.

  17. Nate says:

    Last winter was our first winter experience the joys of heating oil, which was insanely expensive compared to the natural gas furnaces we’re used to. About halfway through the winter we switched to heating the whole house up to 65 in the morning using the boiler and then maintaining the temperature in our living room during the day and bedroom at night with space heaters. I figured it save us several hundred dollars over the rest of the winter. Heating the full house up once per day insured that the rooms without space heaters were at least bearable and not in danger of freezing any pipes.

  18. Nate says:

    Like others have commented, 45 degrees is generally considered to be far too cold to avoid frozen pipes in colder climates. Trent sounds like he’s willing to risk it, but I wouldn’t be. Getting much lower than 55 can put you at risk. We had a pipe burst once when the internal temperature was in the 60s but the external temperature was well below 0.

  19. Finance Nerd says:

    @#9 — I totally agree, safety was my first thought.

    Running a space heater in the room everyone is in is one thing, running it in a hallway when everyone is asleep is something different. I don’t think I’d feel comfortable running one at night, regardless of how safe it claimed to be.

  20. Gretchen says:

    With 3 cats, this isn’t even a debate for us and I’m surprised it is with the three small children as well.

    The 25 W furnace thing makes no sense.

  21. Baley says:

    For clarification: we did find a cool-to-the-touch space heater that has an automatic switch off feature in case it falls over, so I’m not concerned about its safety, though we wouldn’t leave it around the baby unattended. Also, maybe I like it warmer because I’m from Tennessee. I keep trying to turn the thermostat down, but then I get cold and turn it back up. So, I’m trying to save energy, but I’d rather be comfortable. Thanks for all the tips! :)

  22. Vicky says:

    I used to do this when I lived in Oklahoma. Where I live now, um, yeah, I let it get do 60 degrees. I’m perfectly fine in pajama pants and tops, sometimes a robe, slippers, and throws on the couch. It makes the dogs extra cuddly.

    Oh, and sometimes… if the oven is dirty… I’ll … clean the oven. Because it heats up the whole house! But that’s a very rare occasion, and I’m not sure it would save money, but if it were dirty… yeah.

  23. jim says:

    It sounds like Trent has an electric forced air furnace. My house has the same type of heat. Electric heat is less common in colder climates because its more expensive. Electric heating systems are more common in warmer or milder climates where heat isn’t used as much.

    Trent is paying $12 for 100kWh of heat. That would put out about 341k btu. You can get that amount of btu from a 90% gas furnace with about $4 in natural gas. So it would cost about 33% as much to heat that home with a natural gas furnace.

    Its possible that natural gas service isn’t available where Trent lives. Otherwise the home builder really cheaped out with the electric furnace and lack of gas given the cold climate in Iowa. Propane heat might be a feasible alternative in that situation. Cost for propane would be roughly halfway between electric and gas around $8 for 341k btu.

  24. Jeannine says:

    Let’s just say that I wouldn’t want to put my heinie on the toilet seat in the part of the house that doesn’t stay warm all day. Sometimes there is a limit to being frugal – everyone has to find their own.

  25. AnnJo says:

    Maybe i’m making some elementary mistake, but Trent’s math seems way off to me.

    A 1,500 watt heater, even running full-blast for a full 24 hours, will use only 36 KWH. The way Trent describes his usage can’t possibly add up to 75 KWH.

    Where I live, the electricity price is about 8.3 cents per KWH, or just under $3 for a full day of full-blast 1,500 watt heating. I don’t see how it can possibly cost $9 a day for Trent to run his heater the way he describes. Even at 12 cents per KWH, which I believe is more common outside the Bonneville Power area, it’s probably costing him less than $3 a day if he’s running it at 300 watts most of the time.

  26. AnnJo says:

    For those who shiver at the idea of a 60 degree house temp, it’s really a matter of returning to some of the techniques our grandparents or great-grandparents used to keep warm.

    That temperature can be perfectly comfortable if you’re dressed for it. If I’m home for the day in the winter, I’m wearing silk long-sleeved longjohn tops and bottoms, under a fleece or wool shirt and pants, and Costco’s wonderful merino wool socks. I keep a light wool scarf around my neck and if I am sitting for a long time and start to feel cold, I might bring it up over my head.

    Every chair and sofa has a throw of some kind on it and we use them. When I boil water for coffee, tea or cocoa, I might fill a hot water bottle with the extra water and put it on my lap if I’m sitting or in the bed if I’m going to bed.

    It’s just a slightly different way of living, and once you get used to it, it’s perfectly comfortable.

  27. Johanna says:

    Good catch on the math, AnnJo. I should know better by now than to skim over Trent’s numbers without questioning them.

  28. Carlos says:

    Having lived in Japan for many years, we didn’t have central heating. We actually used kerosene stoves (much more advanced than the ones here). For the family room, we had a low table. Over this table was a large blanket. We sit under this table with our feet and draw the blanket up. Under the table is a special radiant heater. This is called a kotatsu. TO buy an imported one is $$$. I have pondered building one. It is very warm. Of course, we also have split air A/C that go in the ceiling (towards the top). They heat and cool.

    I recommend everyone get an energy audit… often at a discount with your local utility. Find out where you are losing heat. Consider spending the money on a high efficiency furnace. Warp your duct with TekFoil Foil Insulation. Seal your cracks with Handi-Foam. Check your weather stripping. Add plastic to your windows during the window for an added thermal barrier. Check out some thermal greenhouse plastic film which is more rugged than the cheap big box store stuff. Keep your curtains closed. For large windows, get thermal curtains. Wear more layers. Get a programmable thermostat… they are cheap. After living overseas, I have to say we have become pretty wasteful of energy here.

  29. jim says:

    AnnJo, You’re right about the math. I believe instead of 75kwh it should be 7.5 kwh.

    1500 W x 10 minutes = .25kwh
    300W x 24 hours = 7.2kwh
    total = ~7.5kwh

    Maybe the 75kwh total came from addding in the amount his furnace runs in that same time. I assume he doesn’t simply use a little spaceheater sparingly and turn off the furnace all together. (?)

  30. valleycat1 says:

    AnnJo & jim, I had some questions about Trent’s calculations too, after running his numbers through a calculater I found online – a cost of heating worksheet (that’s the Google term I used). I couldn’t get the #s to jibe with what he came up with.

  31. Maya says:

    I had the opposite experience as Trent, although maybe it’s due to degrees. When we first decided to lower the thermostat from 65 to 60 we got a space heater for the bedroom. The plan was for my husband to turn it on at 5am when he left for work so that I wouldn’t be so cold as to not be able to get out of bed at 7am. Once I was up and dressed, I turned off the space heater. Our hope was that running a space heater for 2 hours a day, 5 days a week would be cheaper than keeping the thermostat at 65. But what happened was that our electric usage went up and our gas usage (for the furnace) barely changed. Maybe if we had made a larger change to the thermostat, and hadn’t been living in an uninsulated leak bucket with single-paned aluminum frame windows, the story would have been different.

  32. Gretchen says:

    If he is talking about totally electric, forced hot air is indeed very inefficent.

  33. Jane says:

    I always find it really interesting how much people’s thermostat setting varies across this country. I personally like 68 degrees, although even with that I still get cold if I am sitting for a longer period. I used to be a real grinch about heat and insist that we keep it at 63 during the day and 55 at night, but now that we have kids, we’ve raised it. It’s 63 at night and 68 during the day. If you keep your thermostat lower than 68 degrees, I definitely think you should have the courtesy to raise it when you have company. Lots of people aren’t used to anything under 70 degrees. I was annoyed at my mother, because she had some elderly women over for lunch once and left her thermostat at its regular 63 degrees. They were probably very uncomfortable.

    Since we installed a new high efficiency gas furnace, I’ve noticed that we can keep our thermostat higher and still pay less than we used to. This is very nice, because it allows me to not feel as guilty about keeping the house at a comfortable temperature.

    We are avid space heater users, but I don’t necessarily think it saves us money. But when I go to take a shower or to put the kids to bed, it’s just easier to turn on the space heater in the room for a few minutes than to go downstairs to the thermostat to raise it.

  34. Electricity is to expensive in New York. We have a number of zones in our house that we can turn on and off. It saves a lot letting some areas of the house get cold and only heating the places we stay.

    We also found putting in a wood burning stove or pellet stove saved a lot more money as well. I am sure it would not take that long to payback the initial cost depending on your situation. Especially if you are in that room most of the time.

  35. AnnJo says:

    @34, KC,

    I have a woodstove in the kitchen/family room area that also heats (and usually overheats) the upstairs master bedroom.

    Last winter I compared the cost of heating with the type of wood available to me by the cord (fir and alder) versus my other option, electric wall units, and determined that on a per-BTU basis, wood was a little cheaper.

    But keeping a wood stove going full-time and especially controlling its output to keep a stable temperature, is not always easy. It needs to be tended. We use it now only when we get a particularly cold spell or when the power goes out.

  36. Smythe says:

    I’ve tried 60 degrees indoors and it’s just too uncomfortable. I settled on 65 degrees when we’re home, and 55 degrees when we leave the house and during sleeping hours. After some deliberation I decided against space heaters for reasons of up-front costs, safety, and practicality. I use an electric blanket though and love it.

  37. Sara says:

    When I bought my house, the builder told me not to set the thermostat any lower than 55°F in order to avoid the risk of pipes freezing. I keep mine at 56°F during the winter. I have natural gas heat, and my all-time highest monthly gas bill was $128, which is less than $5/day (and that is inflated because it was based on estimated usage, and my actual usage was lower).

  38. Tom says:

    I like 65 during waking hours and 60 at night. We get a lot of solar gain from our south-facing windows during the day, that 65 can turn into 70 with no furnace help on a cloudless day when we bake something for dinner. Still my wife would prefer it to be warmer :)
    It is incredible how fast you can adjust to temperature change though, I almost break into a sweat at my in-law’s house where it is 70F around the clock and they run a humidifier too. I agree with #33 Jane about turning up the heat when company comes over, as a courtesy.

  39. steve in w ma says:

    You don’t need a sleeping room to be warm. I normally sleep in a 45-50 F deg room in the winter. A light continuous polysester comforter or two on the bed and you’ll be totally comfortable at that temperature range. Also, if you’re sitting on a couch reading, working on a laptop, or watching tv, just throwing a sleeping bag or comforter over you will keep you very comfortable in a mid-40 deg room.

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