Warming a bed with an electric blanket for half an hour costs less than boiling the kettle for a hot water bottle. A 70W under-blanket on full for 30 minutes uses 0.9p of electricity at the October 2026 price cap of 26.32p per kWh. Heating the 1.33 litres that two-thirds fills a 2-litre bottle, from 10°C tap water to boiling, takes at least 3.7p.
Leave the blanket on all night and the answer flips. Eight hours at full heat costs 14.7p, four times the bottle. Which is cheaper depends on how you use the blanket, and the blanket costs £8 more to buy.
The verdict, 28 September 2026
- One hot water bottle fill costs about 3.7p: 1.33 litres heated from 10°C to 100°C needs 0.139 kWh. Boil a full 1.7-litre kettle and it is 4.7p.
- A 70W electric blanket costs 0.9p for a 30-minute pre-warm, 7.4p for four hours and 14.7p for eight hours on full.
- Used only to warm the bed, the blanket saves about 2.8p a night. Its pence-back point on the £8 price gap is about 290 nights, roughly two winters.
- Left on for four hours or more a night, the blanket costs more than the bottle and never earns back its price.
- Over a winter of 150 nights: £5.51 for the bottle, £1.38 for a blanket pre-warm, £11.05 for a blanket on four hours a night.
| How you use it | Per night | A winter, 150 nights |
|---|---|---|
| Hot water bottle, one fill (1.33 L) | 3.7p | £5.51 |
| Hot water bottle, full 1.7 L kettle boiled | 4.7p | £7.02 |
| Electric blanket, 30-minute pre-warm | 0.9p | £1.38 |
| Electric blanket, 1 hour | 1.8p | £2.76 |
| Electric blanket, 4 hours | 7.4p | £11.05 |
| Electric blanket, 8 hours | 14.7p | £22.11 |
What a kettle fill really costs
Heating water takes a fixed amount of energy: 4.186 kilojoules for every kilogram raised by one degree. Our hot water bottle guide says to fill a bottle to two-thirds, which is 1.33 litres in a 2-litre bottle. Raising that from 10°C to 100°C takes 0.139 kWh, or 3.7p at the October cap.
That is the floor. A kettle loses some heat to the air and to its own body, and most people boil more water than they pour. Boil a full 1.7-litre kettle and the floor rises to 4.7p. In midwinter, when the cold tap runs nearer 5°C, the same 1.33 litres needs 3.9p.
The pence-back point
On 28 September 2026 the Carmen double under-blanket was £19.99 on Amazon UK and the Revitale 2-litre hot water bottle £11.99, a gap of £8.00.
If you switch the blanket on 30 minutes before bed and off when you get in, it saves about 2.75p a night against a bottle fill. It pays back the £8 after about 290 nights, which is roughly two winters of 150 nights.
If you keep the blanket on while you sleep, it costs more than the bottle every night and never pays back. A blanket left on for four hours costs 7.4p against 3.7p.
| Blanket use | Blanket per night | Saving against the bottle | Pence-back point |
|---|---|---|---|
| 30 minutes | 0.9p | 2.8p | About 290 nights |
| 1 hour | 1.8p | 1.8p | About 435 nights |
| 2 hours | 3.7p | None | Never |
| 4 hours | 7.4p | Costs 3.7p more | Never |
Which one to use
Use the electric blanket to warm the bed, then switch it off. That is the cheapest way to get into a warm bed, and it avoids handling a kettle of boiling water at bedtime.
Use a hot water bottle if you want warmth that lasts into the night without anything plugged in, or if you sit up in bed reading for a couple of hours first. One fill costs 3.7p however long you keep it, and it costs £8 less to buy.
How we worked it out
| Item | What we did |
|---|---|
| Electricity rate | 26.32p per kWh, the Ofgem cap for 1 October to 31 December 2026, direct debit, Great Britain average. Standing charge left out. |
| Hot water bottle | 1.33 litres, two-thirds of a 2-litre bottle, raised from 10°C to 100°C. Energy = litres × 4.186 × temperature rise ÷ 3,600, in kWh. Kettle losses are not counted, so this is the least a fill can cost. |
| Electric blanket | The Carmen double under-blanket’s 70W rating from its Amazon UK listing, at full heat the whole time. Lower heat settings cost less. |
| A winter | 150 nights. |
| Prices | Amazon UK, read 28 September 2026. |
| The pence-back point | The price gap divided by the nightly saving. For a 30-minute pre-warm: £8.00 ÷ 2.75p = about 290 nights. |
What this comparison could not check
- We have not measured either on a meter. The bottle figure is physics for the water alone, and the blanket figure is its rated power.
- How much heat each keeps in the bed through the night, which depends on your duvet and your room.
- The temperature of your cold tap, which changes through the year.
The two we priced
Carmen Double Heated Under Blanket, 70W
£19.99. 0.9p to warm the bed for 30 minutes on full at the October 2026 cap, from its 70W rating. Carmen lists overheat protection.
The catch: Left on all night it costs 14.7p, four times a hot water bottle fill, and it is smaller than a double mattress at 120 × 107 cm.
See it on AmazonRevitale Luxury 2L Hot Water Bottle with plush cover
£11.99. About 3.7p of kettle electricity for a two-thirds fill at the October 2026 cap, and nothing to plug in. It is the best overall pick in our hot water bottle guide.
The catch: It needs a kettle of near-boiling water every night, and it cools as the night goes on.
See it on AmazonLook Into earns a commission on qualifying purchases made through the Amazon links above, at no extra cost to you. It never changes the arithmetic.
Common questions
Is an electric blanket cheaper than a hot water bottle?
For warming the bed before you get in, yes. A 70W blanket on full for 30 minutes costs 0.9p at the October 2026 cap of 26.32p per kWh. Boiling 1.33 litres for a hot water bottle costs at least 3.7p. Left on all night, the blanket costs 14.7p and the bottle is cheaper.
How much does it cost to fill a hot water bottle?
About 3.7p at 26.32p per kWh for 1.33 litres, two-thirds of a 2-litre bottle, heated from 10°C to boiling. Boiling a full 1.7-litre kettle costs about 4.7p.
How much does an electric blanket cost to run per night?
A 70W blanket on full costs 0.9p for 30 minutes, 7.4p for four hours and 14.7p for eight hours at the October 2026 cap. Lower settings cost less.
Is it cheaper to boil a kettle or use an electric blanket?
One kettle fill for a hot water bottle costs about the same as two hours of a 70W electric blanket on full, about 3.7p at 26.32p per kWh.
Compare more
- All our running-cost head-to-heads
- Meaco Arete One vs Arete Two 12L: the Two is cheaper per litre in every room Meaco publishes
- Meaco Arete One vs Arete Two 20L: 0.7p a litre apart, and the Two costs £110 more on Amazon than direct
- Meaco Arete One 12L vs MeacoDry ABC 10L: same night, different cost per litre
- Meaco vs Pro Breeze 12L dehumidifier: one publishes its wattage, one does not
- Ninja Dual Zone AF300UK vs Philips 3000 Dual Basket: 3p a cook against a £28 price gap
- Ninja AF300UK vs Tefal Easy Fry Dual Zone: nine years of cooking to earn back £62
- Ninja AF300UK vs AF400UK: the bigger one costs more per cook and less per litre of drawer
- Electric blanket vs heater: 1.8p an hour against 17.1p and up
- Oil filled radiator vs fan heater: watt for watt, exactly the same bill
- Best hot water bottles UK
- Best electric blankets and heated throws UK
Sources
- Ofgem, energy price cap unit rates and standing charges (1 October to 31 December 2026)
- Look Into, best hot water bottles UK, including the fill-to-two-thirds safety advice
- Amazon UK listings for the Carmen Double Heated Under Blanket (B0CHS28R48) and Revitale Luxury 2L Hot Water Bottle (B078RQHZPB), wattage and prices read 28 September 2026