What It CostsBig Load Running Costs
Four loads that are not appliances so much as household decisions. Each one can be the largest line on the bill.
Electric shower running cost
The biggest thing you switch on all day, for the shortest time.
Underfloor heating running cost
Priced by the square metre, not by the appliance.
Electric water heater running cost
Usually the second largest number in an all-electric home.
EV charging cost calculator
Battery, percentage and your tariff — including the loss the car never mentions.
Hot tub running cost
It heats whether anyone is in it or not. That is the whole cost.
Pool pump running cost
Halve the speed and the power drops to an eighth. Really.
These four are different from the rest of the site. A television is a habit; a hot tub is a decision, and one that shows up on the bill every month whether it gets used or not. Each of the loads here is capable of being the single largest item in a household’s electricity use, and each one has a lever attached that makes a real difference.
For a car it is where you charge and when. For a pool pump it is speed, because power rises with the cube of flow and halving the speed cuts the power to an eighth. For a hot tub it is the cover. For water heating it is the thermostat setting and the tank’s insulation. None of those is a tariff decision — they are all things you can measure this week.
Frequently asked questions
Which of these is the biggest?
Usually water heating, because it runs all year for everybody who has it — commonly 3,000 to 5,000 kWh a year in an all-electric home. A hot tub is close behind and beats it in winter. An EV depends entirely on mileage: 10,000 miles at 3.5 miles per kWh is about 2,900 kWh, roughly the same as a water heater.
Is charging an EV at home cheaper than petrol?
Almost always, and often by a factor of three. The comparison to make is cost per mile: an EV at 3.5 miles per kWh and $0.17 per kWh is about 5 cents a mile, against roughly 12 to 15 cents for a petrol car at 30 mpg. Public rapid charging is a different question — it can cost two to four times the home rate.
Why does the calculator add a charging loss?
Because the meter counts more than the battery receives. Between the wall and the cells, the onboard charger, the cables and the battery’s own thermal management lose energy — typically 8 to 15% on AC home charging, more in cold weather. A car’s dashboard reports what went into the battery; your bill reports what left the meter.
Can a pool pump or hot tub be run more cheaply?
Both respond enormously to small changes. A pool pump on a variable-speed motor at half speed uses roughly an eighth of the power, because power rises with the cube of flow — that is the single biggest saving available on this page. A hot tub lives or dies by its cover: a waterlogged or cracked cover can double the standing cost.
How we calculate this
Sources: