Gas vs Electricity - user test results wanted

tomsidebottom

I think it'd be good to have a load of people compare the cost of running their boiler compared to the cost of running one electric fire. People that take part could put their results as replies to this post and we could see how all the results pan out. Here's mine...

Heating your entire house with gas is cheaper than heating one room with electricity. Well it is for us anyway and we have 9 radiators in our house.

I just did the calculations, and checked them twice (I'm doing a physics masters - so although it's easily possible that I did it wrong, I think there's a reasonable chance of getting it right) and the kWh conversion of the gas boiler going at full rate was 1.80kW. I got one of those free electricity monitors and checked how much our electric fire uses - it was 1.81kW (interestingly this didn't go down even when the fire was on low).

So basically in terms of kWh heating the entire house uses the same amount of energy as heating just our front room, which is pretty amazing.

So the cost per hour of heating the front room with the electric fire is 17.5p per hour, and the cost of heating the entire house is 5.9p per hour. Actually it would be less to heat the entire house than that because our boiler has two rates that it runs at - a full rate and a half rate. I think the full rate is just to get the temperature of the water up to 75 degrees, then once it's reached 75 degrees it starts working at half rate just to keep it there.

Glad I finally got around to doing that anyway - though I'd share my findings. I think I'll be ditching the electric fire. :beer:

macman

I think you'll find that your boiler going full rate will be a lot higher output than 1.8kW! If not it could not possibly heat the whole house. Look at the rating for that make and model. A modern boiler will modulate and burn less gas.
Your electric fire is probably 2kW. Again, look at the rating plate. The cheap monitors are notoriously inaccurate.

penrhyn

There are no central heating gas boilers I am aware of that have an output as low as 1.8Kw.
My modest and very old Ideal standard uses around 12 Kwh of gas which provides around 9 Kwh of heat to the radiators.

When the rooms are up to temperature the amount of energy needed to maintain it is dependent on the outside temperature and level of insulation.

If your electricity monitor is not following the load provided by the electric fire you are not using it correctly, try testing it with an electric kettle.

Over to you Dr Cooper.

HappyMJ

It is cheaper heating only one room with an electric fire rather than using gas central heating but in using the electric heater the rest of your house will be cold.

My test results...

One room 2kW electric heater - (12p/kWh) 24p per hour on maximum.
8 radiators 11.72kWh output boiler/14.65kWh gas input - (3.5p/kWh) 51p per hour on maximum setting.

However, if I used 3 or more electric heaters at once to have a warm house throughout then the gas boiler is much cheaper. Even if I used 2 electric heaters although cheaper the heat from the gas boiler heats more area for almost the same price. Replace your own figures to get your own rates.

jalexa

tomsidebottom wrote: »

...the kWh conversion of the gas boiler going at full rate was 1.80kW...

Give us the raw data, i.e. the start and finish meter readings, the elapsed time and whether the meter is imperial or metric and we will help you with the conversion:D

tomsidebottom

I suspected that I'd made an error - turns out I was misled a bit by something written on my gas meter, "0.071 ft^3/REV", which I interpreted as every time the little clock type dial went round once then that represented a usage of 0.071ft^3, which I found out this morning is not the case at all. One complete rotation is just 1ft^3, as I'm sure you all know - ee well.

I'm going to write out what I did - it'll be a bit long winded but at least I'll have a clear record of what I did.

So, I decided to do a slightly longer test, so I ran my central heating on full for about 90 minutes, and I started the test as the red digit (the 10ft^3 dial on the far right) moved to its next digit - so giving me a clear reference point. After about 90 minutes I went and waited for the red digit to turn again and noted the time. The result was that the boiler had burnt exactly 70ft^3 in 1:45:27, which was 6,747 seconds. This works out at 37.35ft^3/h, which is 1.058m^3/h. Multiplying this by the correction factor of 1.02264, and then by the calorific value of 40 and then dividing by 3.6 (I got these steps from here http://www.ukenergy.co.uk/pages/gas-kwh.html) gave my a kWh value of 12.02. We pay 3.273p per unit for our gas, which means an hour of heating like I just did cost me 39.3p.

The electric fire is indeed 2kW and we pay 9.66p per unit for our electricity, so using the heater to heat the room for one hour costs us 19.3p

So not quite as I first expected - the 0.071ft^3/REV thing threw me until I actually counted the rotations my self!

Let me know if there's anything else I did wrong in my calculations.
Cheers.:T

HappyMJ

12kW per hour for your boiler seems quite low. What model and type is it?

Anyway, you pretty much have it spot on electric heating one room 19.3p/hour and gas heating whole house 39.3p/hour.

The REV counter is a spinning arrow that might have a 0 at the top and a 0.5 at the bottom of it. That is the 0.071m3 per revolution counter.

penrhyn

You may well be paying 9.6 p for your secondary units, but you should average out them out with your primary units ( probably around 22p) as these will be costing you more. I suspect your average cost of electricity will be more like 14 -15 pence /Kwh.

Check your bill for details.

HappyMJ

penrhyn wrote: »

You may well be paying 9.6 p for your secondary units, but you should average out them out with your primary units ( probably around 22p) as these will be costing you more. I suspect your average cost of electricity will be more like 14 -15 pence /Kwh.

Check your bill for details.

Doesn't that then skew the figures somewhat?

If I did that then electric heating is much cheaper all the time.

My actual figures would then be
Electric heating one room 20.5p per hour.
Gas heating whole house 61.1p per hour.

My electric rates are 25.893p,15.908p,4.715p and my gas rates are 7.532p and 2.644p. My usage figures that I used are 5,000kWh electric 55% at night (I use an electric immersion heater to heat water at night as it's cheaper especially in summer when gas is always 7.532p/kWh) and 11,000kWh gas.

LittleMissAspie

HappyMJ wrote: »

One room 2kW electric heater - (12p/kWh) 24p per hour on maximum.
8 radiators 11.72kWh output boiler/14.65kWh gas input - (3.5p/kWh) 51p per hour on maximum setting.

How do you work out the gas input figure?

Also does this presume that the appliance will be going full blast for an hour? Because in your example I'd have thought that the heater would need to be on for 5-6 times longer than the radiators to get the house or room to the same temperature. This would make gas less than 51p per hour but to get the actual cost you'd need to do some testing with a thermometer to work out how long each appliance needs to get up to the right temperature. And that depends on the weather too.

penrhyn

Shouldn't be a problem for a MSc:D.