# Do you know how much taking a shower or filling your bath costs?

Everyone is screaming about energy costs. Wouldn’t it help if we told people what everything costs and let them make their own choices?

Heat maths isn’t very hard, it’s just a bit of addition, multiplication and most importantly getting the units right. We love a crazy unit when it comes to heatpumpery; it’s a thin veil we hide behind to look clever. Don’t worry, I’m not going to explain it all here. I’m a big fan of making the maths much more accessible to homeowners.

If you look at your gas or electricity bill or metre it reads in kWhrs or kWh (or kilo watt hours).

Very few people know how big or heavy a kWh is, but they do know how much they pay for them. My house is 100% electric so I pay 33p for every one of the little fellas I use.

A kilo Watt hour is the amount of energy you use if you turn on a 1,000 Watt (a kilo Watt is 1,000 Watts) heater, or light or fridge or anything else electrical for one hour. If you turn on a 3 kW kettle for 1 hour you use 3 kW hrs of energy – that costs a quid in my house.

Here are a few useful rules of thumb for you to work out where your money is going.

How much does it cost to take a shower or bath in your house?

A 100 litre bath or a10 minute shower uses about 4 and 1/2 kWh of heat.

If you use electricity to heat that 100 litres of water (either in an electric shower or using an immersion heater) it will consume 4 1/2 units. In my case at 33p per unit that’s £1.50

If you have a gas boiler it uses a bit more than 4 1/2 units of gas, because your boiler is not 100% efficient, so we will round it to 5 units. Gas is 7.5p a unit so its £0.35 for the same shower.

A heat pump is a bit better, because we steal 2 free units of heat from the air in the garden for every unit of electricity we use from the mains. So to get our 4 1/2 units we squirt in 1.5 units at 33p a unit or 50p worth of electricity.

Your neighbour with the solar panel gets the electricity for nothing when it’s sunny –so their hot water is essentially free.

If you have a 300 litre hot water cylinder, it’s not difficult to work out that it will take 3 x 4 1/2 units or 13.5 kWh to heat it up once a day. That’s £4.50 if you use normal electricity, £1 if you use gas and £1.50 for a heat pump.

Simple right?

So kids, get out of the shower sooner, don’t fill the bath so high and don’t leave the taps running. It feels like the 70s again.

How much do electric appliances cost?

There are 9,000 hours a year if you plug anything electrical in and leave it on all year it uses 9 kWh for every Watt it draws.

Your phone charger is typically 10 Watts, so it will use 90 kWh a year, that’s £30 a year.

And that hideous gas boiler you’ve got on the wall draws 90 Watts when it’s running and the damn thing would use 800 kWh of electricity a year if it was on 24/7 – that’s £267.

#### This is not a throttle

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19677 kWhs
2 years ago

Brilliant piece Graham. Simple, illustrative and to the point, with everything spelled out in black and white.

439 kWhs
2 years ago

Hi Graham

Good article, the only query – the 10 watts phone charger at £30.

My USB C Fast Charger only draws 10 watts when its charging a device, stand-by and plugged in the wall, mine uses less than half a watt as per EU Directives on stand-by draw. New TVs and many other appliances also have to comply with this Directive.

My phone is charged for 2 hours per day, 22 hours it is stand-by.

• 20 watts for 2 hours by 365 days 14.6kwh – £2.82 per year
• 0.3watts for 22 hours by 365 – 2.4kwh – £0.80 per year

My charger is 17kwh/annum and £3.62 per year to run.

However:

Something that really was a shock, I have a Sainsburys 4 slice toaster and one day, I noticed it felt ‘warm’ in the corner. Assuming where there is heat, there is power consumption, got out my trusty power meter.

26watts stand-by!!!

227kwh per year without even cooking toast. £75 per year and apart from the saving grace of Solar and Batteries saved my pocket, it is an offensive amount of stand-by power (26 times more than the Plasma TV). I still have the toaster but it is now on a Timer Socket which switches itself off after 15 minutes.

I checked the whole house a few years but didn’t bother with the toaster, stupidly assuming that it only drew power when clicked down.

Just goes to show

CHECK EVERYTHING

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