There is an old principle in keeping warm cheaply: heat the person, not the building. An electric blanket is the clearest example of it. Warming the small space immediately around your body costs a tiny fraction of bringing a whole house, or even a whole bedroom, up to temperature, and on a cold night the difference in cost is enormous for very similar comfort.
Why heating the body wins on cost
To warm a room you have to heat all the air in it and, through that, the walls, furniture and everything else, and much of that warmth then leaks away to the colder outdoors and gets replaced again. An electric blanket skips all of that and puts a modest amount of heat exactly where you are. A typical electric blanket or heated throw draws somewhere in the region of fifty to a hundred and fifty watts, against the two or three thousand watts of a fan heater or the far larger output of central heating. Putting those figures into the running cost calculator shows the gap starkly: a few pence for an evening under a blanket, against pounds for heating the house.
Underblanket, overblanket and heated throws
There are a few forms and they suit different uses. An underblanket sits on the mattress beneath the sheet and warms the bed, often used to take the chill off before you get in and then switched off or turned low to sleep. An overblanket lies on top like a duvet and warms you as you lie under it. A heated throw is a portable version for the sofa, draped over you while you watch television or read. All work on the same cheap principle, and a heated throw in particular can let you keep the living-room heating lower through an evening because you are warm under it regardless.
The running-cost comparison
Consider a winter evening. Heating the living room with central heating or a portable electric heater warms the whole space at a cost of pounds over a few hours. Sitting under a heated throw drawing a hundred watts or so costs a few pence for the same period, while the thermostat can sit lower because your body is warm. At bedtime, warming the bed with an underblanket for half an hour costs almost nothing, against the expense of heating the bedroom to stay comfortable all night. The blanket does not replace heating the house entirely, but it lets you heat it less, which is where the saving lands.
Safety, which matters here
Electric blankets are safe when looked after but deserve respect because they combine electricity, heat and bedding. Buy one carrying the proper safety marks, check it regularly for fraying, scorch marks or damaged wiring, and replace an old or worn one rather than nursing it along. Follow the instructions on whether it can be left on overnight, since many modern underblankets are designed for all-night use on a low setting while older or cheaper ones are meant only for pre-warming. Do not use one that is creased or folded in a way the maker warns against, keep it flat, and never combine a blanket with a hot-water bottle. Unplug it if in doubt.
When each makes sense
Heating the person is the smart, cheap choice when one or two people are sitting still in the evening or warming a bed, which is most of the time the question comes up. Heating the room or house properly still matters when there are several people spread around, when you need the whole space comfortable for activity rather than sitting, or to keep the building above the point where damp and cold cause problems. The two work together: keep the house at a sensible base temperature as the thermostat settings guide describes, then top up your own comfort cheaply with a blanket or throw rather than cranking the heating for everyone.