Cost Effectiveness for heating your house. Oven versus Heating oil

[Traab]

So here is the conundrum. Its chilly, we dont want to turn on the heat for the house yet, so instead we turned on the stove to heat up the kitchen and dining room we are in. I wondered which is costing more money, the electric oven set on bake, or turning on the heat and burning oil. I dont know any specific numbers so I doubt I will get an accurate answer but I figured a ballpark estimate would do.

[Ninja_Prawn]

Well, I'm an M&E engineer, so this ought to be my time to shine. But what you're asking depends on so many factors that you haven't mentioned that it's not really possible to say anything constructive to it.

It's certainly possible to have a building where the oven can double as the primary source of heating, but most modern buildings (and indeed, ovens) are not designed to work like that. So I'd assume in general that it won't be efficient to use the oven instead of the actual heating system. Even if you only need heat in two rooms, your heating system must have some kind of controls on it, surely?

[Traab]

Well, I'm an M&E engineer, so this ought to be my time to shine. But what you're asking depends on so many factors that you haven't mentioned that it's not really possible to say anything constructive to it.

It's certainly possible to have a building where the oven can double as the primary source of heating, but most modern buildings (and indeed, ovens) are not designed to work like that. So I'd assume in general that it won't be efficient to use the oven instead of the actual heating system. Even if you only need heat in two rooms, your heating system must have some kind of controls on it, surely?

The only controls it has is a temp control where it shuts off once it reaches the specified amount. It heats every room in the house concurrently. I just was wondering about the electric bill versus the cost per gallon of heating oil. And really, the stove works well, heat it to 400, open the door for awhile to let the heat out, close and repeat. Keeps these two rooms surprisingly decent. I wouldnt use it for anything other than warming the kitchen/dining room as its not THAT good a heater but since we tend to stay in the dining room (its where our computers are lol) it was a good workaround. And yeah, i figured it was very much so a long shot as it requires likely knowing the cost of oil per gallon versus the cost of electricity, plus the amount of electricity the stove uses versus oil the furnace uses and time both are activated to achieve the end goal. But I figured might as well ask out of idle curiosity in case the answer was just blatantly obvious one way or the other. Like, "Omg ovens draw SO MUCH POWER to heat up! Constantly forcing it to stay on to replenish its internal temp would cost you a lot of money!" or, "Meh, we are talking probably 2 bucks either way at most in cost, so it doesnt matter."

[Mechalich]

An oven is designed to heat the space inside of it, not the surrounding area. It has no means to disperse heat and is actually insulated to retain a lot of the heat inside the oven for better cooking efficiency. By using the oven as a heating device you're wasting a lot of energy keeping the oven walls at a very high temperature and relying on heat diffusion to spread the heat across the room, which is inefficient, especially as you'll end up heating the ceiling more than anything else.

However, the idea of heating only the room you are using rather than the whole building in the case of an insufficiently specific heating system is a good one. Rather than trying to use your oven though, you should just purchase a space heater. That will be both much more efficient and also considerably safer as leaving your oven on is a significant fire hazard.

[factotum]

Electric heating has a big advantage over direct heating with gas or oil, namely, the heat is kept entirely within your house--you don't lose a significant portion of it up the chimney. That also means that it won't be drawing fresh, but cold, air in from outside to replace what's been lost in burning the fuel. I would definitely recommend Mechalich's approach of getting a dedicated electric heater rather than using your oven to do it, though--it's not like they're particularly expensive, and a dedicated heater will simply do a better job of heating the room because that's what it's designed to do.

[DeTess]

Your central heating could be more effective than your oven trick (and would be far, far safer than burning oil to heat, as that's just going to kill you from CO poisoning unless you ventilate your rooms really well). A quick bit of research is that ovens tend to use around 2400 W on average at higher heats(source). An older house uses about 200kWh/year/m2 to heat, while a more modern houses uses 100kWh/year/m2 or less (source). Assuming you run central heating for about a 120 days a year or so, each square meter requires 35-70 W of power from your central heating to warm. This means that if you've got an average fairly modern oven, it'd only break even if your houses is bigger than between 35-70 m2, depending on how well isolated everything is and stuff.

If you want to figure this stuff out for yourself, simply find out how much watts your oven pulls, and how much energy you use each year for heating to get a ballpark estimate.

[jayem]

Are you cooking, that could shift the balance?
Though I'd imagine this uses so much less because it can turn off the element when at temperature as supposed to never reaching it.

[Ninja_Prawn]

requires likely knowing the cost of oil per gallon versus the cost of electricity, plus the amount of electricity the stove uses versus oil the furnace uses

Aye, at the very least. Also floor areas, plant efficiencies, types and layouts of heat emitters, what your walls are made of, outside air temperature and what temperature you want to achieve inside, whether or not the oven has a fan, how leaky your windows and doors are, what kind of extraction you've got over the oven, etc. etc...

I feel like guessing at average numbers isn't really going to be much use here, since you've obviously got a somewhat unconventional building. I mean, is the furnace driving some kind of centralised warm air system? If so, do the diffusers not have dampers? Or if it's something like LTHW trench heating, are there not TRVs? How big is this building, and when was the heating system installed?? It seems very strange that you can't control where the heat goes.

Plus I have no idea what energy prices are like where you are. Are oil-fired furnaces common in your part of the world? You hardly ever see them over here because gas is so much cheaper...

[Erloas]

Without knowing the cost of electricity or oil it is almost impossible to say. But in general burning fuels for heat is significantly more efficient than using electricity, which is why most places use fuels for heating. The only places that generally use electricity for heating are places that don't need a lot of heating and/or the infrastructure for things like natural gas don't exist (and usually the reason the infrastructure isn't there is because it isn't needed because it doesn't get that cold).

Unless the house is very old and changing over the heating wasn't possible/practical it can be assumed that oil heating is a much cheaper option than electric because otherwise it would be electric, since electric systems are less complex and the infrastructure is already there.

So what the question ends up mostly coming down to is: are you saving enough by only heating 2 rooms with electricity to be better than heating the entire house with oil. Are those two rooms half the house? 1/6 of the house?
Is the oil system like a radiant heat boiler type of system or a forced air? Forced air is pretty much just as efficient running frequently and only rarely, whereas most boiler systems do better when the system is already warmed. Boilers need a lot of extra energy to get the whole system warmed up to the point where it starts heating, by contrast a forced air system goes from "completely off" to "heating" in about 30-60 seconds.

Of course the option of "bake cookies" once a day and also happen to heat up the kitchen while your doing it is a win-win, you get cookies and the heating is a byproduct.

[Chen]

The only places that generally use electricity for heating are places that don't need a lot of heating and/or the infrastructure for things like natural gas don't exist (and usually the reason the infrastructure isn't there is because it isn't needed because it doesn't get that cold).

Or places where electricity is cheap. It gets ****ing cold up here in Montreal but most heating is electric. Hydro power here is very cheap ($0.06 per kwh for the first 40kwh per day then about 9 cents/kwh for more).

[Ninja_Prawn]

But in general burning fuels for heat is significantly more efficient than using electricity

Point of order: no it's not.

Electric heating is approximately 100% efficient - electricity in = heat out, less whatever tiny fraction gets used in the controls electronics. When you burn fossil fuels, you get out maybe 85 to 95% of the chemical energy out as heat (yes, condensing boilers can pull energy out of the exhaust air too, but even these top out at about 105%), but you've got to remember that you lose on average 10% of the heat in distribution, and you need to spend an additional chunk of energy running things like pumps and fans. And don't get me started on 3-port control losses!

The reason people use fossil fuels (especially gas) for heating is because they're cheap. Where I live, gas is about 3p/kWh; electricity is pushing 15p/kWh.

[Erloas]

Or places where electricity is cheap. It gets ****ing cold up here in Montreal but most heating is electric. Hydro power here is very cheap ($0.06 per kwh for the first 40kwh per day then about 9 cents/kwh for more).

That definitely comes into it. Some parts of the world are a long way away from sources of fuels so they're going to be relatively more expensive because of transportation costs. There are probably also a lot of considerations for things like earthquakes, having natural gas lines all over the place in an area that might shift even a little bit make them a lot more dangerous.

Point of order: no it's not.

Electric heating is approximately 100% efficient - electricity in = heat out, less whatever tiny fraction gets used in the controls electronics. When you burn fossil fuels, you get out maybe 85 to 95% of the chemical energy out as heat (yes, condensing boilers can pull energy out of the exhaust air too, but even these top out at about 105%), but you've got to remember that you lose on average 10% of the heat in distribution, and you need to spend an additional chunk of energy running things like pumps and fans. And don't get me started on 3-port control losses!

The reason people use fossil fuels (especially gas) for heating is because they're cheap. Where I live, gas is about 3p/kWh; electricity is pushing 15p/kWh.

No, you're just forgetting all of the steps before it gets to your house. Almost nothing generates electricity directly: coal, natural gas, solar, wind, hydro, nuclear, etc. all take some other form of energy and changes it to electricity. That electricity is then changed to a type that is better for transmission, then goes through any number of substations and changed back down to whatever voltage is used in your area (USA being 120, most of EU being 220/240, all sorts of variations) and every single one of those steps have inefficiencies in them.

Now granted something like wind or hydro you're not that worried about the initial generation inefficiencies but you still have transmission losses. And while an industrial scale natural gas boiler is going to get more energy out of each liter/cubic foot(whatever measurement you want to use) of natural gas, it isn't going to make up for the other inefficiencies in the system. So burning that natural gas directly in your furnace in your house is going to be more efficient than burning it at a power plant, turning that into power, sending that power to your house, then turning that power into heat.

Of course, as above, cost comes into it a lot too. If you've got really cheap electricity or more expensive natural gas/other fuel, then it might not matter which is more efficient. Even as more and more electrical generation comes from natural gas, it's still cheaper to burn the natural gas yourself then to have a power plant do it for you.
Overall efficiency probably isn't the best term in this case, because total cost is more important than efficiency. Effective is probably a bit better of a word, but even that doesn't really catch everything.
The shorter version is that virtually every place that has easy access to natural gas will use that for heater rather than electricity.

[Douglas]

A major factor here is what kind of heating system your house has. There are two broad categories I'm thinking of - a heating system can:

1. generate new heat, or
2. transfer existing heat from the outside environment

The second variety can be much more efficient than the first in terms of heat added to your house per unit energy spent. I'm pretty sure all ovens work by generating heat. If your house's heating system generates heat then it may be worth doing some math to compare. If your heating system transfers heat then I think it's a pretty safe bet that it's more efficient than the oven even if it has to heat a larger portion of the house.

[Ninja_Prawn]

If your heating system transfers heat

You're totally right that transferring heat is more efficient than generating it, but Traab has said their central heating involves an oil-fired furnace. Granted, you can build a heating system that transfers heat using a furnace (presumably based on some kind of absorption chiller, running back to front), but the chances of finding something like that in a domestic property are so vanishingly slim that I think we can safely ignore them.

[HouseRules]

A major factor here is what kind of heating system your house has. There are two broad categories I'm thinking of - a heating system can:

1. generate new heat, or
2. transfer existing heat from the outside environment

The second variety can be much more efficient than the first in terms of heat added to your house per unit energy spent. I'm pretty sure all ovens work by generating heat. If your house's heating system generates heat then it may be worth doing some math to compare. If your heating system transfers heat then I think it's a pretty safe bet that it's more efficient than the oven even if it has to heat a larger portion of the house.

The heat exchange fluid should not be frozen or not have the external environment be frozen for it to stay effective.
If the outside environment freezes over the heat exchange, then it becomes inefficient.

[Rynjin]

"Fun" fact: a significant percentage of house fires in areas with cold weather are caused by people trying to heat their house with their ovens or stoves.

So...don't do that. Especially if it's just "chilly" and not actually cold.

[LordEntrails]

Get a space heater. Yoru oven is remarkably INefficient at heating anything but itself.

[wumpus]

Point of order: no it's not.

Electric heating is approximately 100% efficient - electricity in = heat out, less whatever tiny fraction gets used in the controls electronics. When you burn fossil fuels, you get out maybe 85 to 95% of the chemical energy out as heat (yes, condensing boilers can pull energy out of the exhaust air too, but even these top out at about 105%), but you've got to remember that you lose on average 10% of the heat in distribution, and you need to spend an additional chunk of energy running things like pumps and fans. And don't get me started on 3-port control losses!

The reason people use fossil fuels (especially gas) for heating is because they're cheap. Where I live, gas is about 3p/kWh; electricity is pushing 15p/kWh.

Except that the power company likely used fossil fuels to produce the electricity. So while the oil heating can get significantly close to 100% (with most of the losses going up the chimney), the power plant has to deal with the inefficiencies of power generation (and transmission). Just the theoretical efficiency of a Carnot engine should be less efficient than an oil furnace, and you will lose at least 20% (probably more, I haven't really dealt with it) to get that power to your house.

If you had a natural gas range (or oven), that should be cheaper to operate (although I suspect that thanks to monopoly pricing vs. competing oil companies it won't be), but then you have an open flame in the kitchen, so don't do that. I also doubt that many people have oil furnaces after natural gas is available (plenty of natural gas is being "pumped" in the USA).

The only thing more efficient than your furnace would be a heat pump, and then only in certain ranges (probably not much below freezing). Even better would be a ground-based heat pump that would take heat from near the ground's surface (presumably wrapped around the basement when the house was built): where I live that means about 50 degrees Fahrenheit (about 10 Celsius) of heat/cooling year round (so it would equally ideal for air conditioning instead of futilely trying to dump heat into a 100 degree summer day). This sort of thing allows "greater than 100% efficiency" because it isn't using the energy you are paying for to create the heat, only to move it from place to place.

[factotum]

Except that the power company likely used fossil fuels to produce the electricity.

Firstly, no they didn't--I think the proportion of grid power being generated from renewables and nuclear is between 33% and 50% depending where you are. Plus you might have your own solar panels or who knows what else. Lastly, a power station is a much larger structure than a typical house and so has much more room to install scrubbers in the exhaust, meaning it's likely cleaner and more efficient than the in-house heating as well.

This is all ignoring the obvious savings that come from only heating the rooms you're occupying rather than the entire house.

[Ninja_Prawn]

proportion of grid power being generated from renewables and nuclear

Well... it varies massively. Where I am (Scotland), grid electricity is mostly hydro. In France it's 70% nuclear. In the US, where I assume most forumites live, coal and gas are the main energy sources. So wumpus and Erloas aren't wrong to say that burning oil at home is 'more efficient' than burning gas in a power plant. Transmission losses are real.

But that's somewhat beside the point for the scenario we're being asked to look at, because of reasons like...

Plus you might have your own solar panels or who knows what else.

We've been asked to consider a heating system. Traditionally, when you're talking about the efficiency of a heating system, you talk about the heat put into the space divided by the energy put into the system. It's a sensible approach, because everything outside of that is going to be outside your power as a heating engineer. And by that approach, electric heating systems will almost always put out more heat per kW of input than fossil fuel systems. Hence my original statement.

Sure, cost effectiveness is a separate issue (and the price of mains electricity probably reflects the inefficiency of the network to some extent). But we can't really comment on that without knowing what Traab pays for energy.

[tomandtish]

The only controls it has is a temp control where it shuts off once it reaches the specified amount. It heats every room in the house concurrently. ....

What can also matter in this case is where the thermostat IS. It's certainly an option to close the vents and doors in rooms you aren't using. Those rooms will end up being cooler.

But location matters. Case in point: In our house the thermostat is in the upstairs hall. The hall itself doesn't have a vent. So if you close doors and leave vents open, then the rooms will be warmer (if heating) or cooler (if cooling) then the hall, because the hall doesn't have a direct vent. Likewise, the downstairs is always cooler than the upstairs.

[HouseRules]

In northern regions that are Heating bias:
Heating gives 4 degrees Fahrenheit gap per floor.
Cooling gives 10 degrees Fahrenheit gap per floor.

[Eternal Dharma]

Dotting this thread as a survival enthusiast.

[Chronos]

If we're looking at "efficiency" on a per-dollar basis (as the OP probably is), then we need not consider the efficiencies of power generation or fuel transportation at all, because those will already be taken into account in the price the consumer pays for those utilities.

And even if the oven is very well-designed to keep its own insides hot, and not the kitchen, every joule of energy it consumes will still end up heating the kitchen. Ultimately, all of the energy in either case will end up as heat. The only "inefficiencies" to deal with are heat that ends up leaving the house (heating up the wrong parts of the house will, in the long run, matter only to the extent that that puts it closer to leaving the house). So the best thing to do, if possible, is to improve the house's insulation. Get the insulation good enough, and you can get all the heat you need from the things you'd have running in the house anyway, like the human occupants, their computers, and the normal cooking you'd do. In fact, large buildings often need to run the air conditioning even in the winter, because they're too efficient at keeping all that incidental heat.

[Traab]

Well finally got all the air conditioners out of the windows so we can stop using space heaters for our legs and turn on the furnace. Seriously, this and its opposite time of year are the most miserable. Having to haul like 5 air conditioners up from storage in the basement and put them in the windows, taping up all the gaps to avoid insect issues and such is exhausting work and murder on your back. Putting them back down for winter is just as bad. After all, gotta clear out the spider webs, bird nests and other random debris before closing everything down, of freaking course all the acs will have water trapped in them to one extent or another making a mess as soon as they get tilted sideways, and getting them down a narrow staircase around multiple corners and properly stored makes my poor back want to stage a mutiny. Plus I always manage to mess up at least once, grab it from the wrong way, and get tiny slices in my hands or arms from the metal grates and such pushing into my flesh. Thank god I only do it once every 6 months or so. :p

[factotum]

Can't you just close the vents in the aircon units and leave them installed all year?

[Traab]

Can't you just close the vents in the aircon units and leave them installed all year?

Not really. My windows suck, my acs suck, and there are gaps everywhere mostly sealed by tape. Even if they did have the option, and most dont, it wouldnt help much and its a lot easier to seal the windows for winter with that shrink wrap stuff if im not trying to get it around the air conditioners.

[Ninja_Prawn]

Sounds like you need a whole new house, tbh.

[Traab]

Sounds like you need a whole new house, tbh.

I really really do. We have been renovating room by room but its like one per year as thats expensive. Maybe some day we will remove the asbestos.

[Jay R]

If heating your home with oven technology were cheaper than heating it with heater technology, they'd be building the heaters with oven technology.