Unfortunately some of the companies have been deliberately using bad English and have been muddling people up. Efficiency is the ratio of what you get out compared to what you put in – how many kWs the appliance uses to how many kWs you can use. Example; an open coal or gas fire is about 20% efficient, in other words, 80% of the energy released goes up the chimney not into the room for you to use. Electric cookers are 100% ‘efficient’ as they have no chimney/flue, but electricity if not a fuel, but a means of transmitting energy, so it is generated from oil, gas, coal etc. This is inefficient so electricity costs around 12p/kW. An oil fired Thornhill range is about 90% efficient, so you lose 10% through the flue, but using oil directly (instead of paying to have it changed to electricity via a power station) the oil cost around 5.5p/kW, so the cost to you is 5.5/.9 = 6.1p/kW. About half that of an electric cooker.
So if you want to heat your kitchen with 2kW per hour energy, an Everhot, Redfyre or Total Control Aga range cooker will cost you 24p/hour, but an oil Thornhill range will cost 12.2p/hour. It’s as simple as that, but of course they don’t want you to know that. I replaced an Electric Total Control Aga range cooker last December for an accountant and he measured the cost at over £900 a year, even with his free electricity from his solar panels on the roof. He estimates he is saving £500 a year with his Thornhill Range pellet cooker, bringing his running cost down to £400 a year with a warm kitchen. Hope this helps, Regards Graham