Electric heater in one room vs centrally heated whole house

DemiDee

Hi all

I live in a 2 bed plus box room semi detatched house. Over the past month, because of how necessary it's been to have the heating on, I've been trying to work out whether it is more cost effective to have my electric eco heater on in the one room I use during the daytime, or to have the central heating on throughout the house instead (it's more cost effective to keep all radiators on if using the central heating since the boiler has to work harder otherwise).

I've discovered that the electric heater is costing around 13p per hour, whilst the central heating is costing about 44-48p per hour. Of course, I imagined that heating a whole house would cost more regardless, but just couldn't help wondering whether this sounds excessive for a house of average size. Even the e.on rep I spoke to seemed to think that this was high, and I imagine it's because we have a very old combi boiler - about 15 years old, in fact.

I'd be interested to learn of other MSE-ers thoughts on central heating vs electric heaters. The latter get so much bad press, but in fact, if you purchase the right type, they're not so bad at all.

molerat

44-48p is ridiculous. At the coldest I was using 15p per hour heating my whole 3 bed detatched, including keeping the conservatory warm, 24/7 using my 25 year old boiler, the same as a 2Kw electric heater.

How do you reach the 44-48p figure ? Check your meter for m3 or ft3. If you are using the wrong figure your calculations will be 3 times what they should.

DemiDee

Thanks, Molerat. The readings are unfortunately accurate. I took readings over several hours, making a note of the readings on the hour, every hour. Did this for a few days and then called up E.on to check out the costs..and lo and behold, it's 44-48p per hour. which is really quite worrying.

I can't understand it, since E.on have assured me that I'm on the best tariff too: SaveOnline 4, which is:

Normal units up to 2680 = 5.34 pence
Normal units = 2.68 pence

I'm currently still on the higher of the two rates.

Cardew

Firstly the name electric 'eco' heater is just marketing rubbish - the heater is no more, or no less, economical than any other electrical heater.

Your statement "it's more cost effective to keep all radiators on if using the central heating since the boiler has to work harder otherwise" is also complete nonsense I am afraid.

At '13p an hour' I assume you are talking about a 1kW heater.

The simple answer is to turn off all the other radiators in the house and just use the one in the room you are using and it will be much cheaper than using electricity.

HappyMJ

DemiDee wrote: »

Thanks, Molerat. The readings are unfortunately accurate. I took readings over several hours, making a note of the readings on the hour, every hour. Did this for a few days and then called up E.on to check out the costs..and lo and behold, it's 44-48p per hour. which is really quite worrying.

I can't understand it, since E.on have assured me that I'm on the best tariff too: SaveOnline 4, which is:

Normal units up to 2680 = 5.34 pence
Normal units = 2.68 pence

I'm currently still on the higher of the two rates.

You would (or at least should) have used up more than 2680kwh of gas so far so should be on the secondary rate by now. That's only enough gas for my gas boiler for 30 days on max at 6 hours per day. Or 2 months if 3 hours per day is sufficient. That's only an hour in the morning and 2 in the evening which should leave enough heat in the house for another few hours till you go to bed. So I'd use the 2.68 pence rate to figure it out.

HappyMJ

DemiDee wrote: »

(it's more cost effective to keep all radiators on if using the central heating since the boiler has to work harder otherwise).

While that is in a way true on my boiler all (6-7) radiators on makes the efficiency 80% (using 15kw gas per hour) and cutting down to 2-3 radiators and reducing the temperature of the boiler only reduces it's efficiency to 75% (and using only a maximum of 12kw gas per hour). The gas usage per hour is a bit lower. Yes it works harder cycling on-off a bit more but it's not a big difference.

DemiDee

Cardew, I guessed as much regarding the name of the electric heater. However, this one does seem extremely energy efficient. It's a 1.5kw heater. The info about using just one or some of the radiators and switching others off being less cost effective came from an e.on rep who seemed very knowledgable. Unfortunately, it's not as simple as just switching them all off and using the one in the office, since this one's only very small and doesn't give off much heat unless the rest are on too, so it's been an 'all or nothing' situation for some time.

HappyMJ (love the username!), I'm not anywhere near having used the higher ratings. My bill goes from 30th November, and there's a long way to go before I reach the amount needed to get onto the reduced rates.

Tupperware_Queen

I have my heating on, set low at 16 degrees throughout, then warm the living room with the electric fire.

Jon_Tiffany

HappyMJ wrote: »

While that is in a way true on my boiler all (6-7) radiators on makes the efficiency 80% (using 15kw gas per hour) and cutting down to 2-3 radiators and reducing the temperature of the boiler only reduces it's efficiency to 75% (and using only a maximum of 12kw gas per hour). The gas usage per hour is a bit lower. Yes it works harder cycling on-off a bit more but it's not a big difference.

A modern combi boiler has to be very highly rated to provide hot water on demand. This often means that it is over sized for central heating. If your boiler is only heating one or two rads its likely that the return temps willl be high and the boiler will not be in condensing mode and therefore less efficient.

Even though the boiler will not be running at its most efficient, it should still be cheaper than electric heating.

aelitaman

DemiDee wrote: »

Thanks, Molerat. The readings are unfortunately accurate. I took readings over several hours, making a note of the readings on the hour, every hour. Did this for a few days and then called up E.on to check out the costs..and lo and behold, it's 44-48p per hour. which is really quite worrying.

I can't understand it, since E.on have assured me that I'm on the best tariff too: SaveOnline 4, which is:

Normal units up to 2680 = 5.34 pence
Normal units = 2.68 pence

I'm currently still on the higher of the two rates.

Those two rates are spread out over a year. Also they are not units on the meter but KWh units.

So 2680 / (52 weeks x 7 days) = 7.36kwh per day at the expensive rate. This equates to about .66 units on a metric meter or .24units on an imperial meter then you are on the cheaper rate.

Seeing as you say you thought you were on the expensive rate then this would be

48p / 5.34 = 9Kwh every hour that it is on. Just to let you know this figure is possible as my boiler burns 6.6Kwh per hour when the temp out side is 4C or so and it burns 11Kwh per hour when the temp is minus 5 oustide and I have no insulation (very old house). But a decently insulated modernish house with DG and cavity wall and roof insulation would be less a lot less.

But back to your cost after the first 40mins of use during the day you would be on lower rate so 9 x 2.68p which is 24,12per hour.

But if a 1Kw or 1.5 Kwh electric heater is enough to keep the room that you are using during the day warm then that is all the gas that should be required to keep that room warm as well. If I guess the number of rads at 3 bedrooms, 1 landing 1 bathroom, 1 hall, 1 lounge, 1 dining room, 1 kitchen and 1 cloakroom making 10 in total. This means each rad is using .9Kwh when on.

Seeing as gas is about 1/3rd the price of elecy you should be able to leave three radiators on during the day for the same cost as having the one electric heater on.

DemiDee

Now my head really hurts! I asked the E.on rep to explain the two different rates to me and I'd assumed that what you have said above was the right way of calculating it, but she categorically denied this, and said that it's based on your bill date for each quarter. So, if your bill is set to 30 November, for example, then the payments on your higher rate begin on that date and continue until you reach the lower rate.

My head is spinning. I thought it would be so easy to calculate whether 6 hours of electric heater use would compare favourably or otherwise to the same in central heating throughout the house...but it's actually just made things even more confusing and complicated. Argh!!!