A heat pump and an EV on one tariff

An EV is easy to please. It sits still from midnight to six, it can take 35kWh in that time on a 7kW charger, and it doesn't care that the house is asleep. So the EV tariffs put their cheap window there: Intelligent Octopus Go is 8p a kWh from 11.30pm to 5.30am, with more smart slots when the grid is quiet. The tariff comparison has the rest of them.

A heat pump is not easy to please. It works hardest when the house is coldest, which is early morning and early evening, and it can't store much of its work: a well-insulated house holds heat for a few hours, a draughty one for one. So the heat pump tariffs put their cheap windows in the day, and they charge you more than a normal tariff the rest of the time. Cosy Octopus gives you 4am to 7am, 1pm to 4pm and 10pm to midnight, then a peak rate 50% above the day rate from 4pm to 7pm. That peak is exactly when a heat pump and a cooker and a kettle all want power.

Put both in one house and every tariff is a compromise. The car is happy on an EV tariff and the heat pump pays the day rate; the heat pump is happy on a heating tariff and the car charges at 14p to 17p instead of 8p. The question is which compromise costs less, and the answer depends on how much of the heat pump's work you can push into the cheap hours.

The test is whether the cheap rate applies to the whole meter or only to the car. Four tariffs pass it.

• Intelligent Octopus Go. 8p a kWh for six hours a night, for everything in the house, plus extra smart slots when Octopus schedules the car outside the window. You need a compatible car or charger. Octopus's own tariff guide, updated on 14 September 2026, says a house with a heat pump and an EV should pick this one, because the heat pump can run in the same six hours.
• Cosy Octopus. Three windows a day, eight cheap hours in all, for the whole house. Sunsave's June 2026 comparison puts the cheap rate at 14.53p, the day rate at 33.28p and the 4pm to 7pm peak at 51.68p, though the exact numbers vary by region. You need a heat pump, electric boiler or electric radiators to join. The 10pm to midnight and 4am to 7am windows give the car five hours a night, which is 35kWh on a 7kW charger.
• British Gas Heat Power. Half price from midnight to 7am and 1pm to 4pm: 16.8p against 33.6p in Sunsave's June figures. British Gas's own page says it suits any make of heat pump, electric heating, EV and battery, and the seven-hour night window is the longest of the lot for the car. There's a £75 exit fee.
• E.ON Next Pumped. Three rates: 16.926p from 10pm to 6am, 21.298p for most of the day, and 39.853p from 4pm to 7pm, in the same June comparison. The middle rate is the interesting one: it's below the price cap, so a heat pump that can't move its work still isn't punished for it.

The one that doesn't pass is OVO Charge Anytime, 14p a kWh for the car and nothing for the house. OVO used to sell a matching Heat Pump Plus add-on at 15p, but it was withdrawn from February 2026, so an OVO household now has a cheap car and a full-price heat pump. Octopus sells Cosy and Intelligent Go as alternatives, and its guide picks Intelligent Go for a house with both.

Two numbers to start. The car does 8,000 miles at 3.4 miles per kWh, which is 2,350kWh, all of it chargeable in whatever cheap window the tariff has. The heat pump uses 3,200kWh a year, which is the typical figure in Sunsave's comparison for a house that used to burn about 12,000kWh of gas; I'd expect a big draughty house to use nearer 5,000, and a snug new one under 2,500.

The heat pump is the hard part of the sum, because you can't put all of it in the cheap hours. The table assumes 40% of its electricity falls in Intelligent Go's six night hours, with a pre-heat before 5.30am; 60% falls in Cosy's eight hours across the day, with 5% at the peak; half falls in British Gas's ten hours; and on E.ON a third goes at the night rate, most of the rest at the middle rate, and a tenth at the peak. Change those shares and the order barely moves, because the car's 2,350kWh at 8p is what wins it for Intelligent Go.

On the price cap at 26.32p, with no tariff at all, the same year is £619 for the car and £842 for the heat pump, about £1,460. Every tariff in the table beats that, and the best beats it by over £500. The rest of the house isn't in these figures: on the whole-house tariffs it pays the day rate outside the windows, which the tariff comparison works out at £100 to £220 a year for a typical 2,500kWh, and which a dishwasher timer mostly gets back.

The car is the easy half: set it to charge in the window and forget it. On Intelligent Go, Octopus schedules it for you and the whole house drops to 8p whenever the car is charging, even outside the window. The scheduling guide has the steps for each car and charger.

The heat pump takes three habits. First, pre-heat: set the thermostat to bring the house up a degree or two in the last hour of the cheap window, 4.30am on Intelligent Go, 6am on Cosy, so the fabric of the house is warm before the day rate starts. Second, don't let it go cold: a heat pump running steadily at a low flow temperature uses less electricity than one hauling a cold house back up at 5pm, so a steady 19 or 20°C beats “off all day, on at teatime”. Third, if the tariff has an afternoon window, use it: on Cosy and British Gas, 1pm to 4pm is when to run the hot water cylinder and top the house up before the peak.

A smart thermostat that knows your tariff does all three without you. If yours doesn't, two schedules on the heat pump controller, one for the cheap hours and one for the rest, get most of the way. And on the tariffs with a 4pm to 7pm peak, the cooker and the tumble dryer are dearer than the heat pump: move those first.

• Most homes with both. Intelligent Octopus Go. The car at 8p is the biggest saving on the page, the six cheap hours warm the house before dawn, and Octopus itself points a heat-pump-and-EV household here.
• Car or charger not on the smart list. British Gas Heat Power. Seven cheap hours a night and three in the afternoon, any car, any charger, and 16.8p is still half the price cap. Mind the £75 exit fee.
• Big heat pump, small mileage. Cosy Octopus. If the house uses 5,000kWh of heating and the car does 4,000 miles, the three windows suit the heating better than the night does, and the car still gets five hours at 14.53p.
• A heat pump that can't shift. E.ON Next Pumped, because its middle rate is under the price cap, so the hours you can't move cost you least.
• Already with OVO. The car is cheap at 14p and the heat pump isn't. Moving supplier is worth £200 to £300 a year on these figures, which is more than most people's reason for staying.

Whichever you choose, do the sum with your own two numbers, the car's miles and the heat pump's kWh from last winter's bills, before you switch. The Octopus comparison covers the case where Agile tempts you, and solar changes the sum again if you have panels.