Hi Michele, All these cookers use about the same kW consumption – around 3kW per hour when at 200C. The faster they heat up the less you will use, because you can control the cooker better. So an Aga range cooker 3kW x 24 hours = 72kW a day. But oil is about 5p/kW and electricity about 12p /kW.
Oil Thornhill Range, Agamatic/New Aga range cooker electric say 2 hours/24hr at 3kW = 6 kW at 12p/kW electric, 6p/kW oil. But in winter you will need a radiator in the kitchen, if you use an electric cooker or you will be heating your kitchen at a cost of 12p/kW instead of oil at 6p/kW. It won’t make any difference is you have an oil fired boiler running a radiator or the Thornhill Range on as both are about 85-90% efficient. Is the site of the cooker on an outside wall/can you have a balanced flue oil? The flue costs then are only about £300! If not a chimney will cost about £1,250. Hope this helps. Regards Graham