6个月前

Is it cheaper to use a plug-in oil radiator to heat an individual room, or run the central heater to heat an individual room and living room?

With winter coming up, I have two options for home heating.

Central unit

I can use the central unit and close/open vents throughout the house to heat up only the individual rooms I want. This would heat up rooms very quickly. However, to make this work, the living room with the thermostat will also need to be heated so that the thermostat reads the proper temperature. The living room is by far the largest space at about 2.5 times the size of the largest room.

Oil-filled radiator

I can use an oil-filled radiator to heat up an individual room. This would be much slower, but I wouldn't have to heat up the entire living room. However, the oil-filled heater might not be as efficient as the central unit. I don't know. I plan to rarely heat up the living, no more than once per month.

Edit: The central heating unit is actually a heating kit made up of a few coils that is added to the central a/c.

Edit 2: Where I live, it might freeze once per year over night for a few hours.

Which would be more efficient on the electrical bill, and would t be considerable or negligible?

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Unfortunately there are way too many variables just to answer that definitively.
If you put a thousand Watt resistive heater in a room 1,000 watts will generate 1000 watts worth of heat give or take. But if you use a heat pump, 1000 watts of power can be used to move 3,500 Watts worth of heat outside to in. Speaking from a theoretical power concept.
If you're heating your entire house to 20 or 30° above ambient, you'll have losses on the roof in every wall, If you're just eating one room all you have are the losses of that room so insulation becomes a weird thing to calculate.
You can't just let your pipes freeze if you're a freezing zone, but generally unless you're central is super efficient, maintaining a comfortable temperature in one room is more cost-effective, heating one room should cost somewhat less than try to heat the whole house no matter what method you're using.
- At last, a reply that understands the difference between heat pumps vs resistive heating.
- You're right.
  If they have a heat pump, it could be cheaper to use that over all.
  *Edit: It's electric resistive heat on a central air system.

If you're in an area that doesn't freeze you can keep the house cold and heat one room with an electric oil filled radiator very inexpensively.
If you're in a place that freezes you need to keep the house warm enough to avoid freezing the water pipes.
Otherwise have fun, heat one room and bundle up everywhere else.
- bundle up everywhere else.
  It should be noted that if you don't need to heat the room you're in, you can also get an electric blanket for $30 or less, and those babies work infinitely better at keeping you warm than a space heater.

Not really an answer to your question, but if you live somewhere that freezes think about where your pipes are.
You gotta heat the bathroom and kitchen and any other rooms that may have pipes running through them, or you’re going to freeze and probably burst some pipes.
Or, you could leave your taps trickling, but that expensive too.

Heating just the room will be overall cheaper. However doing the whole house will be cheaper per square foot because your room isn't insulated against other rooms, just to the outside, so you'll lose a lot of heat to bleed through to other rooms.
Both are just converting electricity to heat which is already a very efficient process. It's unlikely one of them is significantly better at that.

Eating a room sounds expensive. Not just in terms of the materials required, but also paying for the aftermath.
- Oops! Fixed it. Thanks for pointing that out :)
  
  Haha thanks for taking it in good spirits!

Get a cheap thermometer to place in the room you're going to heat and look how much it is off the thermostat and regulate accordingly.
Leaving one room cold while others are significantly warmer might raise the risk of mold, because the warm air might cool in the cold room and condensate on the walls and windows, creating conditions for mold growth.
I look that every room is at least about 16°C as an absolute minimum in winter.
I'm not familiar with mobile oil radiators, but it sounds kind of dangerous to me.
- They are actually one of the safer plug in type heaters.
  
  I thought they burn oil or something, but they just use oil instead of water in a closed system.
  Sometimes I'm dumb. The CO buildup from my version of oil radiator would be deadly.
- Good idea! Thanks for the info and suggestion.

Just an FYI, closing up vents in an hvac can actually cause problems. It puts more strain on the fan unit, which can cause it to burn up quicker. The unit is designed to move a certain amount of air, if you restrict that air, pressure builds up in the system.
A couple closed over an entire system is fine, but closing all but one room would definitely cause problems.
- I have been closing 3 out of 5. Is that too much?
  
  Depends on the unit and whether it was over sized or under sized for the space, but restricting 60℅ air flow is a lot.
  Another thing to consider is that if you later want to heat up the entire house, the unit has to work harder. Sometimes it can be more efficient to just keep the house close to your target temp.

There are far too many variables to know for sure. What fuel does the central heat use? Where is the house built? What sort of sun exposure do you get? What type of house is it? What's in your attic? Basement? How much time do you spend at home during the day?
I would go with the central heat, generally speaking.
Homes are insulated differently depending on where you live, but the exterior walls are usually better insulated than the interior ones. The heat in one room will dissipate to neighboring rooms. You're correct that closing vents will direct the hot air to the desired rooms first. Over the course of the day, some of the energy will disperse and warm other rooms. One space heater might use less energy than your central air, but you will need to run it longer and more frequently.
You may also find that you're keeping the one room hotter because you're always cold in every other room. Getting warm and staying warm are two different physiological processes. Keeping the house at 66 may feel warmer than keeping one room at 72.
Consider what each heat system was built to do. Central air is there to keep the house warm. Central air is most efficient when it is automated to maintain heat. Allowing the space to get very cold every day will cause it to run longer when you feel cold.
Meanwhile, a space heater is a short-term hot spot in a room. It's designed to create immediate warmth in the immediate area. Use it when you are feeling cold to get yourself warm, and then shut it off. If you use each one to do its job, that's probably going to be the most efficient.
The best thing you can do for your energy bill is insulate. Get a temperature sensor, wait for a cold day, bring your entire house up to ~70, and then go hunting for cold spots. Check around window sills and near brick or masonry walls. Airflow through your walls is dollar bills flying out of your wallet. You can place film over leaking windows, replace caulk when it cracks, and fill voids that happen when old insulation breaks down or gets wet. Check your attics and crawlspaces for airflow as well, and consider reflective foil as an inexpensive upgrade if you can get to the rafters.
If everything is properly insulated, all heating and cooling becomes more efficient.

I'm curious to an actual, scientific answer, but I do something similar, and here's my anecdotal results:
I've got one of those electric fireplaces (fancy 1500w space heater basically) in my den, and I usually spend a lot of time in here (it doubles as my WFH office). I'll turn the central thermostat down about 5 degrees and just run the fireplace while I'm working in there. When I'm done, I'll bump the main thermostat back up.
My furnace is gas, and the price keeps rising every year, but doing this over the last 3 years, my gas bill has stayed relatively flat even though the price has skyrocketed. I think it averages me an extra $20 at most on the electric bill which is less than the gas would have cost.
Granted, I live by myself, so I don't have to worry about other people in other rooms getting chilly lol.
- At least where I live gas is significantly cheaper than electric.
  
  Complete opposite here, though both are getting expensive.
  Electric price per kWh has a little more than doubled since I bought this house in late 2019. Gas has nearly tripled, and they haven't even finished easing in the rate hikes yet (public service commission approved the gas company's hikes, but only if they were gradually phased in).

What type of central unit do you have?
- It's a central a/c unit with a heating kit added to it.
  
  Resistive heating elements are inefficient compared to heat pumps, and usually cost more to run than gas.
  If it’s an old a/c system you may want to upgrade it to a heat pump. In many cases you can keep the air handler and resistive heat and only replace the outdoor unit and indoor coil.
  
  It's probably better to use a space heater where and when you need the heat. That central heating kit is basically the same thing, but it's using more electricity providing heat to the entire home, including the rooms you aren't using. Just set the thermostat to a minimum temperature to keep the pipes from freezing.

Pretty sure any serious answer needs to factor in where there insulation sits. It's not only about heating a space but how much you need to heat continually to keep it warm.

I actually did some googling and there are some okay-ish articles debating this topic. All of them said “it depends”, which isn’t really helpful.
It got me thinking, though… how much savings would you need to make it worth it to you? ($20 savings? $100 savings? $500 savings?)
The oil heater is going to cost ~$50 to purchase if you don’t already have one. That means you’ll at least need to save $50 just to break even. So over the winter, your electric bill will need to drop by $50 plus whatever the dollar amount you need in order for it to be “worth the trouble” for you.
If an extra $50 over the winter in savings ($100 total) is worth it to you, I think you have a high chance of an oil room heater getting you that savings over your central heating. I’m doubtful how much more you’d be able to save beyond that. (I didn’t do the math on it, but based on the articles I read, the oil heater is going to be cheaper in general.)
Another thing to consider: The oil heater is likely to be a lot more convenient to use than the central air option and having to close all the other vents in your house though.

Most all forms of heating are near 100% efficient, since it's the waste heat you want. Unless the central heating is using a heat pump instead. Does your central heating use gas heating? If so, using it will probably be cheaper. If it uses resistive heating, the individual unit might be cheaper. But if it uses a heat pump, it might be cheaper to use central again. There are a lot of variables it's hard to know.
- It uses a heating kit that is added to the a/c unit.
  
  Okay, that's resistive heating. So it'll be the same efficiency as a oil heater or any space heater. So heating less space with it will save money.

How cold does it get where you live and which sides are the room and living room on compared to the coldest wind?
If the room you use is on the north side and the cold wind comes from the north, that electric heater is going to get a workout and you lose the advantage of the house having a heat mass that can even out the need to hwat the one room.
If the room is on the south side away from the wind the rest of the house would be a bit of a buffer, making heating only that room less of an energy simk. The number of windows and other ways to lose heat will matter too. If the living room has a lot of windows and other ways to leak heat then not heating it could be an advantage.
If it gets to freezing where you are at I would suggest a combined solution if possible. Set the central heat to a temp a bit above freezing to keep the pipes from bursting (around 55 F) and shut the ducts to rooms you don't care about. The difference in temp to the outside temp is what uses the most energy, and closing that difference has a huge difference on energy costs. Then use the space heater in the room you do care about to reach the temp you want.
This will result in the central unit doing a lot less work than it would to bring the whole house up to temp, but the portable unit wouldn't need to heat the the room and the interior walls nearly as much becuae it would be heating the difference between the central unit at the desired temp. This will probably be the most comfortable/consistent arrangement and likely close in cost to just doing the room by itself.
- It might freeze once per year...maybe. My area is surrounded by trees, so I think wind hitting the house is negligible.
  
  In that case, I still recommend turning on the main thermostat but setting it very low so it only kicks on during extremely low temps as this can help with comfort without much cost at all. The space heater would then do the job in the room you care about to save costs.
  One other thing that I haven't seen mentioned elsewhere and I forgot myself is humidity. While a heater isn't going to change the humidity like an air conditioner that is cooling does, the fan in the unit can even out the humidity in the house and humidity can have a big impact on how the temp feels. Depending on the size of the room and how much air gets circulated, your presence could have a significant impact on the humidity levels.
  I would recommend that whether you run the central at a low temp or not, running the fan for a bit once in a while would be a huge benefit to the home. You don't even need to turn on the heat for that, just the blower. This will help to reduce any damage from condensation throughout the house, and you don't need to open your room to get the benefit. Within the room you are using it might be a good idea to check the humidity levels and look up what the best humidity is for the temp you are aiming for. While that might mean getting a humidifier or dehumidifier if the room is way off, that will most likely be a lot less expensive than the heating cost and you might even find a slightly lower temp comfortable and save more than you spent on adjusting the humidity.

Tp calculate needs way more info that. U would need to know the effective efficiency of the central heating system. The houses per room insulation effect and inter room insulating effect. The heat output of each device. Ambient temperature. Then u could do some thermodynamic analysis to determine which is more expensive. Alternatively u just measure both taking care to compare the getting to temp and maintaining temp separately.
I believe u thermostats are a standard wiring so u can probably wire up a relay and a raspberry pi with a wireless thermostat.

If you're basically living in one or two rooms in an otherwise unoccupied house then the space heater is probably better since you won't have to deal with the thermostat being in another area.
If you're going to need heat in different rooms all over the house then I'd say let the central heat do it's job. You really don't want to deal with running around opening and closing vents and having to warm up another room every time you need to go in there. It will be a pain in the ass and probably cost a lot more.

Run both. Central to keep the house from freezing and radiators to make whichever room(s) comfortable.

What kind of unit is the central system - heat pump? Resistive heating?
There are a lot of details we'd need to determine this, so I don't think we can give you a firm answer. But heat pumps are dramatically more efficient than resistive heating, so if the central system is a heat pump that's probably the right answer. If the central system uses resistive heating then it's probably not much more efficient than the small heater.
- It's a central a/c unit that has a heating kit.
  
  Yeah that looks like resistive heating, so there's no reason to think it's more efficient than the small heater which definitely uses resistive heating. It's impossible to know for certain but my gut says the small heater is the right call - since you're heating a smaller area, there's less surface area to lose heat from, and heat losses are what drives heating costs.

Electric radiator is 100% efficient.
If your central heating works by heating coils with electricity then it's 100% efficient as well. If you heat all the rooms to the same temperature it makes no difference which one you use. If you use radiators but leave some rooms cooler than others then that's going to cost less money.
If your central heating works by burning oil / gas then that's probably going to produce heat for cheaper than electric radiators are. Same applies if it works by heat-pump. Those are 200 - 300% efficient.

Do you not plan on using the living room at all? Because the room you're residing in is the one you definitely want to be warm to avoid mold.
- I kind of like it being cold because I can cuddle up under a heavy blanket or wear my wizard robe.
  
  The problem is that you increase the humidity in the room with every breath. That humidity is going to condense onto the cold walls of your living room and consequently be a breeding ground for mold.

i recommend you avoid polluting the air in an enclosed space. So no oil burning inside the room. The central heating would be a much better option in my opinion
Alternatively, weak (1 to 5 kwh) electric heaters with good placement can heat rather large rooms without wasting nearly as much power
- I think by "plugin" op means electric rafiator filled with some special oil that dissipates heat. So it's still electric just the heating element will heat and circulate oil.
  
  Oh that's pretty cool, sorry for the misunderstanding
- They said oil filled radiator, not oil burning. I expect it's a very efficient electric heater like these:
  https://www.homedepot.com/b/Heating-Venting-Cooling-Heaters-Space-Heaters-Electric-Heaters-Radiant-Heaters/
  If they are trying to keep one room warm and don't care about freezing the rest of the house those are very efficient.
  
  I was thinking of one of those radiators that burn oil, and you have to fill them up before use. Thank you for clarifying!
  ps. the link appears to not work for me? Maybe they have a region block?
- I agree that burning oil would be a terrible idea. In this case, the oil would be in an enclosed radiator that is designed to function as an indoor heater. Thanks for looking out tho!
  
  That is actually pretty cool! In that case, the slowness shouldn't be a big issue. As soon as you've got a comfortable temperature you only need to maintain it

I know a guy that heats his house with those tubular heaters for greenhouses. One for each room and the place is always comfortably warm without being too expensive.

upgrade your house insulation, get a heat pump on the central furnace, and heat the whole house. People have better things todo than closing vents or moving heaters., your central furnace needs most of the vents open to work right.

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