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(Edited to provide additional info)

My wife is looking to buy an old house (I'm guessing 19th century) that'll need a lot of renovating, including the heating system. Renovation works will include (some) insulation and modernisation of the electric system. Actually the part in which we'll be living seems to have been a farm building; what appear to be the old living quarters are in a small attached house that hasn't seen occupation for at least 40y, from the looks of it. Both are built with local limestone (probably raw-hewn "stones" behind a layer of plaster), meaning there's only so much wall insulation you can install without losing precious internal space. But the obligatory energy-loss assessment is surprisingly good, despite the fact there are no double-glass windows except in the attic (thanks, Velux!).

Currently there is a central heating system that runs on fuel oil which also provides the hot water (except in the kitchen), backed up by a fireplace insert (one of those sealed things) in one of the rooms, plus an electric radiator here and there. We're currently in a rented house which also has individual electric heaters. We are used to in-house temperatures that peak at 20°C at most, 18°C being the more usual average; we wouldn't even want it hotter and having to put on 2 extra layers of clothing plus coat before going outside.

Most likely we will be wanting to get rid of the fuel boiler, either ASAP after getting the house or in the year or so following the acquisition. A single fuel delivery is around 1000€ which corresponds to about the number of individual electric heaters we'd need. It would also cover much of the price of an electric replacement for the fuel boiler, depending on whether we'd opt for a model that also provides hot sanitary water (we'd want a hot water boiler anyway).

I've been reading up on the topic and while electric boilers are clearly the least expensive to buy and install (and maintain) they're apparently the most expensive in use, compared to other energy sources for central heating.

I have not found a single text that compares them to a system with individual space heaters. Can anyone here help with that question? In particular, will a central heater burn more energy if you do not heat all rooms all the time (shut off radiators, manually or via a local thermostat)? Will individual heaters heat the room more efficiently for instance because they get hotter (e.g. oil-based ones that are safer and give less dry heat)?

Our budget doesn't really allow for other alternatives that are more economic in use (or greener), like those using wood pellets or a heat pump. I know running costs of such systems will be lower in the long run but you have to be able to finance the initial investment.

Thanks!

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    It doesn't sound like you are NOT using conventional "total life cycle" logic (i.e. Cost of installation + cost of monthly operation for n months) to decide what is best for you. For instance "Cost of a tank fillup" misses the point, conventionally. Perhaps you can describe what economic factors are important to you. – Harper - Reinstate Monica Jun 12 '19 at 14:11
  • There's a lot of stuff up there that isn't relevant to your actual question (inasmuch as I can discern what you're asking). Please revise to simplify and clarify the question. We're not a discussion forum. – isherwood Jun 12 '19 at 14:14
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    What is the cost of a gallon of fuel and a kwh of electricity where you live? – Jeffrey Jun 12 '19 at 14:55
  • Another way to look at costs - if individual electric heaters were more efficient, a lot of people would just do that. Why have a complex boiler system at all if you can just buy a bunch of little heaters to do the same job? – JPhi1618 Jun 12 '19 at 15:11
  • In terms of energy cost, all electric heating methods are 100% efficient. You get the exact same 3.41 BTUs per watt, no matter what. People choose central electric heating with hot water distribution vs individual heaters out of convenience, cost to purchase and install, etc. There's no energy efficiency difference. – dwizum Jun 12 '19 at 19:12
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To answer the main question, an electric boiler is exactly as efficient at turning electricity into heat as individual electric heaters. However, individual electric heaters allow per-room heating setups; if you only rarely use a room, you can turn the heat down. However, an oil boiler will almost always be cheaper to run than either, unless you live near a nuclear power plant or dam. (Although an oil delivery is expensive, you don't need oil delivered that often.)

However, with this specific property, having a central boiler, plus a fireplace insert, plus individual heaters, tells me that the central boiler is probably not able to keep up with the heat demands of the house. (Side note: relying on a fireplace for heating is a terrible idea. They leak most of their heat to the outside, and add a large draft to the house.) It sounds like the house was made when it was expected that people would wear a sweater while indoors during winter, with the house not being heated to "room temperature". So, the individual heaters were added in order to provide an extra boost, but comfort is still not going to be great, and you'll probably be paying a lot for heating unless you're willing to use the sweater method.

My suggestion would be to keep the boiler for now. Those things have a service life, and you might as well let that service life run out. In the meantime, you should upgrade the sealing and insulation of the house to at least close to modern standards. This will increase comfort and decrease heating load.

(Side note: some houses have in-ground oil storage. These are expensive to deal with, and you do not want that. Make sure you know where the fuel oil is stored.)

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  • The insert is one of those sealed things, so there are no drafts, and heat gets distributed to the large attic room above the fireplace. Keeping the oil boiler for the 1st winter would be an option but if we end up installing electric heating afterwards we'll have lost the fuel costs, in a way. Remember that we do want to install a hot water boiler for tap water. – RJVB Jun 13 '19 at 11:51
  • Also, electricity is probably the cheapest energy source (after fuel oil), thanks to France's nuclear generation. We don't have gas where we live (other than the bottled butane varieties, or LPG in big above-ground outdoor tanks). – RJVB Jun 13 '19 at 11:53
  • Since you're in France, cheap nuclear power makes electrical heating a reasonable option. As for the insulation, rock and plaster walls are actually pretty good, and you should be concentrating on any areas that aren't rock and plaster walls. (Windows, doors, roof, and floor.) – user3757614 Jun 13 '19 at 15:46
  • I think I made a mention of cheap nuclear power somewhere already :) But thanks for confirming the bit about the walls. I'm trying to convince my wife to get real double glass (not just extra panels), and to insulate the roof if not already done (the attic room is one of the nicest in the house, with varnished pine wood panelling that I'd love to preserve). – RJVB Jun 13 '19 at 17:11
  • Note that while a good double paned window is better, new windows are expensive, and you'll be unlikely to make your money back with energy savings in a reasonable time frame. Instead, you should be looking at sealing drafts in windows. – user3757614 Jun 13 '19 at 18:15
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TCO

I am big on Total Cost of Ownership. In this case, it includes the cost of the equipment and also the ongoing cost of fuel. In many areas, electricity costs quite a bit more than fossil fuels (oil or gas) for heating - both space heating and water heating (and combined like a boiler).

Essentially, you have to figure out how much heat you get from 1000€ of fuel oil and how much the equivalent will cost with electric heat. If electricity will also cost 1000€ then the difference is paying it month-by-month instead of a lump sum. If electricity will actually cost you 1500€ then fuel oil starts to make a lot of sense.

All electric heating will cost nominally the same. Electricity in, BTUs out. Comfort may vary depending on how the heat is distributed through the house, but the basic cost doesn't vary much.

Scotty, We Need More Power!

There is also an additional cost to keep in mind if you switch from oil to electric heat and hot water: Upgrading your electric service. An older house designed for oil heat may not have a large enough electric feeder (and panel, etc.) to support full house electric heat and electric hot water. And if you need a meter/feeder/panel upgrade then you may find that you now have to add AFCI, GFCI, etc. to circuits that until now have been grandfathered under old rules. So the cost of installing that inexpensive electric boiler may turn out to be quite significant.

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  • The electric system will have to be updated anyway. And yes, we'd need a higher-capacity electricity contract for central electric heating, but would it be that much more than we'd need for an all-electric household with individual heaters per room, electric stove, oven and hot water boiler? The idea is that you should be able to run all heaters plus the kitchen appliances and then have some margin left. Then again one could reduce the contract and turn off heating in unused rooms (e.g. while cooking) – RJVB Jun 13 '19 at 11:58
  • My point is "The electric system will have to be updated anyway" is not necessarily the case. If you stick with a oil boiler/heating system (existing or new) then you may very well not have to upgrade your electric contract. I am a big fan of "right fuel for the job". For me that goes so far as "electric oven" (more/better features than gas) + "gas cooktop" (finer control of heat), as well as the more common (in my area) "gas heat, gas hot water". I assume you don't have natural gas as an option, but fuel oil should be nearly as efficient (even if not as clean) for heating. – manassehkatz-Moving 2 Codidact Jun 13 '19 at 14:13
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    No, we will have to update the electric system, it is not up to norm. Comes with the territory (old house, (still) owned by an old person)... we'll also have to evacuate some asbestos-based roof panelling and possibly review the connection to the sewer system. Natural gas isn't an option indeed (unless we get an above-ground, outdoor LPG tank...). The big immediate problem with fuel heating is that the odour makes us both feel sick, and the room that might well become the bedroom has a window (too) close to the boiler room. – RJVB Jun 13 '19 at 15:09
  • LPG tank wouldn't be any better than fuel oil - still bulk delivery and still leak/etc. issues. I've never been a big fan of whole-house electric heating - I grew up in a house like that (built during a moratorium on gas installation, which was kind of stupid because the electricity was being produced by gas & (worse) coal) and it was always cold. – manassehkatz-Moving 2 Codidact Jun 13 '19 at 15:51
  • I have no experience with LPG for heating in terms of smells and overall messyness, but you're right, and I know someone who wouldn't want a big tank in her garden. Much of the Dutch electricity is produced by (Dutch) gas, which is costly but at least allows (theoretical) heavy-duty air-cleaning facilities. – RJVB Jun 13 '19 at 17:17
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If you're renewing the building, I strongly suggest to go heat-pump, unless outside temperatures plum in winter under -15°C for long periods.

If climate is mild air-air heat pump (split system) are the best (cool in summer heat in winter and only in desired rooms), if heating is more important than cooling, underfloor with air-water heat pump will be better (you could pass an icy day running on thermal inertia of the building)

For water heating go with a heatpump-fired storage kind water heater, at least 100L/person because heatpump-only mode is quite slow in heating but with traditional backup elements installed (in case HP engine fail), you could get a boiler with also 'auxiliary heat' inlet and hook it up to thermo-solar panel just not to use EE in summer to heat water.

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  • Thanks. If those systems existed without unsightly and noisy heat exchangers we would certainly consider them ... if we also had the budget (the total cost of making both parts of the house livable and up-to-norms is already over 40k€ and that does not include any heating appliances or even a very necessary bathroom refresh). Could an air-water HP be used to drive the existing hot water radiators? That would increase at least the technical feasibility as a mid/long term solution... – RJVB Jun 13 '19 at 15:44
  • @RJVB, yes, you can get air-to-water heat pumps that will supply both potable hot water for showers etc., and also supply water to the existing radiator system. In the UK these are often called "combi-boilers". Here's one example: daikin.com/products/ac/lineup/heat_pump – Nate S. Jun 13 '19 at 17:16
  • @Nate: you mean the "Residential Heat Pump Boiler" which IIUC is sold only in Japan? – RJVB Jun 13 '19 at 17:21
  • @RJVB, I just linked that as an example, not a specific recommendation of what to get. Since I don't speak French I don't think I'd have much luck searching out a local supplier for you (and that's off topic for this site anyway). But I'm sure that type of arrangement is available near you from some other company. – Nate S. Jun 13 '19 at 17:26
  • I did find this page, which claims it's an easy replacement for existing heating solutions: daikin.fr/fr_fr/famille-produits/… (that's probably the residential high-temp type). – RJVB Jun 13 '19 at 17:29
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Heat pumps work better when they interchange with groundwater instead of ambient air. Air is very light, so you have to move a Lot of air to interchange with much mass of it. That's why air heat pumps sound like jet engines.

For one thing, air is always on the wrong side of your desired temperature, so you’re always having to pump heat "uphill". Imagine the day is 35C and you are trying to air condition to 25C. You have to chill the Freon down to 15C to get it to cool your house's air, and it rises to 25C... then you have to "pump it up" to 40C to get the heat to move into the 35C air. This is inefficient, so you have to move a lot of air.

Whereas, you take your 25C warmed Freon and interchange it with 10C ground water. It moves freely. You don't even need Freon and the enthalpy cycle, any coolant would do because you're "pumping downhill".

On the other side, you're better off heating from 10C groundwater than -5C air - it's uphill, but less uphill. There's just more heat to extract.

If you want to do heat-only and use it for water radiators and household heating, then I guess you'd need a water-water heat pump. But if you can get air radiators, you can do air conditioning.

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  • I think I saw an argument not to go for a system using geothermal energy, not sure if that's what you're hinting at here. Either way, we're at about 100m altitude, I have no idea to what depth we'd have to go to hit ground water. There's a tiny river in our village but the property is way above the inundation zone. – RJVB Jun 14 '19 at 11:40

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