Efficiency of a oil filled heater

toolmaker54

If over a 5 hour period I heated a room to a certain temp with outside temperature constant, first using a 1kw heater for 5 hours at a set temperature, then using a 3KW heater for 5 hours set at the same temperature.

Would I in theory use the same amount of electricity at 1kw and 3kw for the 5 hour period.

What I am trying to find is the most efficient use of the heater, as you would a car where the most efficient speed for MPG would be 52mph.

Or are there too many variables to make this calculation impossible.

DTDfanBoy

All electric heaters are 100% efficient.

In this instance using the 3kw heater would use slightly more electricity because it would heat the room to the required temperature faster than the 1kw heater.

The warmer a room is the faster it will lose heat, which is why there will be a slight difference between the two.

rogerblack

100%.

If the thermostat is regulating the 3kW heater to the same room temperature as the 1kW one, the heat-loss through the structure will be the same.
The walls can't 'know' what heater you're using, just their surface temperature, and heat percolates through them according to that.

This varies a little if the thermostat isn't perfect, but not enough to meaningfully measure.

dogshome

OK - A Kwh is 1000 watts delivered in hour, each unit on your meter equals one Kwh and your supplier charges for each one

At the moment , depending on your tariff, one Kwh costs appx. 15 pence so to have that One Kwh heater on for 5 hours will cost roughly 75 pence
The 3Kwh heater will use three times as much electricity over the 5 hours at a cost of £2.25.

These figures are affected by the heater's thermostats - The 3kwh model creates more heat and will warm the room quickly - If it'a small well insulated room the 3Kwh heater will switch itself off when the room is warm, then come on again as the room cools, but if it's a big or draughty room it will just carry on burning money.

There are many types of electric heaters - If you post your room details and hours of heating, you will get advice as to which type is best for you

fishybusiness

The 3Kwh heater will use three times as much electricity over the 5 hours at a cost of £2.25.

Only if it runs constantly, which it won't if said room temp is reached and maintained for the 5 hours.

Bottom line, all other things being equal it will cost the same.

Richie-from-the-Boro

Assuming the heat loss of the structure / the air infiltration loss / the effectiveness of heat gains to the room / [STRIKE]the heating period[/STRIKE] / the thermal mass of the structure [block or timber construction] and the approximate percentage of direct acting required for both economic considerations and accurate control is the same for both tests, there should be no difference worth calculating other than in a scientific / academic sense. The only difference would be the heating period point at which the 1kWh reaches what you describe as the 'certain temp' compared to the 3kWh.

Most energy is lost to warmth leaking out of ~ or cold leaking in to your [property] room in this instance. There is a cancelling out issue in that the U]bad[/U heat leaking out point will be reached earlier with the 3kWh, whereas the U]equally bad[/U cold leaking in point with will continue for longer with the 1kWh.

chris1973

You can't choose a heater and adequately heat a room based on running cost preference and budget alone, it all depends how much heat your room requires to heat it from cold and then keep it at that desired temperature when its cold outside.

For example, if your room requires 4kw/h worth of heat input to heat it to a comfortable level when its 0c outside, then putting a 1KW heater in it will achieve little, other than cost you whatever 1 unit of Electricity costs every hour, but the room will never feel warm enough, and you won't get any benefit from that 1kw/h worth of electricity because the room is leaking / requires more heat than you are actively inputting into it, and you'll soon find that the 1kw heater is nowhere near powerful enough to heat it.

However, put 4kw/h of heat into the same room, and it will warm quickly to the selected temperature, and then cycle the thermostat on/off in order to keep it warm. Yes 4kw of heat will cost more than 1kw of heat, but if the room requires 4kw/h worth of heat, then there is no getting away from that just because you only want to pay to run a smaller heater, and you'll end up either have to foot the cost of heating it with the energy that the room requires, or stay cold.

To find out how much heat you require, enter the dimensions of the room into a room heating calculator, and then observe the 'watts' calculation. Your heater(s) wattage rating should total at least this figure, or ideally higher if your room has poor insulation or is draughty.

http://www.qvsdirect.com/kW-Heating-Calculator-p-50.html

Unfortunately a lot of people don't bother to even work this out, they just buy the cheapest , lowest wattage heater they can find, and then attempt to heat their entire lounge-diner with it, usually resulting in them complaining that despite buying this 'miracle' 600 watt heater, they are are still sat in front of their TV in gloves and a coat - go figure.

If you visit any property with a modern central heating system, you'll probably find that it has at least 2 radiators in the larger living areas, sometimes one of these may even be a double!. This equates to around 5kw worth of heat output, which, even allowing for the efficiency losses between Gas and Electricity (Electricity is 100% efficient compared to a 91% modern Gas Fired Boiler) it still indicates that the room needs quite a significant heat input, and this won't change based on the fact you are intending to use portable electric heaters to provide it, rather than a CH heating system.

grahamc2003

toolmaker54 wrote: »

If over a 5 hour period I heated a room to a certain temp with outside temperature constant, first using a 1kw heater for 5 hours at a set temperature, then using a 3KW heater for 5 hours set at the same temperature.

Would I in theory use the same amount of electricity at 1kw and 3kw for the 5 hour period.

What I am trying to find is the most efficient use of the heater, as you would a car where the most efficient speed for MPG would be 52mph.

Or are there too many variables to make this calculation impossible.

If the rate of heat loss at your set temperature under the conditions you state is greater than 1kW, then your 1kW heater will be on all the time and your set temperature won't be reached. The 3kW heater will reach the set temperature (assuming the heat loss is less than 3kw!), and will use more electricity than the 1kW heater.

If the rate of heat loss at your set temperature and conditions you state is less than 1kW, then both the 1kW and the 3kW heater will reach the set temperature, but (as dtdfanboy correctly stated), the quicker reaching of the set temperature by the 3 kW heater means the 3kW heater will be slightly more expensive (since the heat losses during the climb to the set temperature will be slightly higher).

(Incidentally, kw/h doesn't mean anything - the correct units in this example are kw (for the power), kwh (for the energy) and h (hours, for the time). If you have 1kW used for 5 hours, then you have used 5kWh of energy (whihc is 5 units of electricity)

toolmaker54

Thanks for all the replies, just carried out my own experiment with the oil filled rad in the bedroom which is a size of 3mx5mx2.3m, with one long outside wall, and according to the site chris1973 gave my room needs 1.3kw to 1.6kw to heat it

The starting temp of the room was 12 degrees and was kept with the heater to a constant 17 degrees for a 12 hour period on two separate days from 10am to 10pm door closed and only opening occasionally to enter.

The outside temperature on both days was 6-8 degrees.

The monitoring done on my energy meter plugged into the heater and socket gave me the following results.

Heater set at 2.48kw it used 6.6kw in 12 hours so thats 0.55kw/hr
Heater set at 1.48kw it used 6.84kw in 12 hours so thats 0.57kw/hr