The current maximum price permitted by Ofgem for 1 kWh in GB is 28p.
However the Ofgem price cap doesn't apply in NI, so the price where you are might be very different, Sandy. Looking at sample tariffs on the Power NI website though suggests that 28p is also a good guideline figure for you at the moment.
Re - Z-M's comment @16.43. Sandy isn't trying to "heat a room" - he wants to raise the temperature a few degrees and a fan heater is a perfectly good and efficient way to do this.
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