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?
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.
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.
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.
When my wife first mentioned she was using one, I had the same initial reaction lol
Good idea! Thanks for the info and suggestion.
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.
Tbf some jurisdictions don’t have water bills
Yeah apartments don’t usually pay for water or heat where I live. It’s also a huge waste of water
In Northern Ireland you are just flat out… Not charged for water.
Interesting. Sounds nice.
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.
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.
Depends on the unit and whether it was over sized or under sized for the space, but restricting 60℅ air flow is a lot.
Thanks for your response! I appreciate it. Do you know how I can investigate this further? I would like to figure out if I’m over-stressing my unit because I’ve been doing that for the past ~2 years.
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.
Heating up the house happens so rarely that I can’t remember the last time I did that. It may have been ~2 years.
I’m not an HVAC technician so I wouldn’t know exactly, but I think there’s two things to consider: static pressure and duty cycle. Static pressure is the fan working hard to spin which causes wear on bearings. Duty cycle is how long the machine runs. If your duty cycle is too low then the machine is turning on and off quickly which is bad.
You could look at the size of the unit and there’s some rules of thumb that translate size, climate, and square footage of just the areas you leave the vent open and there are online calculators you can use.
I think the only way to know for sure is to measure the pressure drop across the intake and outflow and see what the fan motor is rated for.
This is a good starting point! Thank you very much
Run both. Central to keep the house from freezing and radiators to make whichever room(s) comfortable.
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!
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.
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.
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.
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.
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.
