7kW vs 22kW home charging: when extra power is useful

Start with three separate power limits

Our charging-time calculator uses the lowest of the vehicle AC limit, charger power and any property limit. For example, a hypothetical car accepting at most 11kW AC on a 22kW chargepoint is still limited to 11kW before any further restriction at the property. A 7.4kW car does not become a 22kW car when connected to different hardware.

Look specifically for the vehicle’s AC charging specification. A headline DC rapid-charging figure describes a different charging situation and should not be entered as the home AC limit. Manufacturer documentation for the exact variant is preferable to a generic search result for the model family. Tesla’s onboard-charger explanation is a useful reference for why the conversion inside the car matters.

References: Tesla UK — What an onboard charger does

Understand the supply question

EDF’s installation guidance distinguishes single-phase homes that can support a 7kW charger from three-phase supplies that can support higher-power charging up to 22kW. That distinction does not mean every property of either type has spare capacity for the equipment you want. The proposed load and installation still need to be assessed.

Ask the installer to confirm the supply type, available charging power and whether a proposed upgrade requires work beyond fitting a wallbox. Do not identify the supply by guessing from a photograph or opening electrical equipment. If an upgrade is proposed, ask who handles each part, what it costs and whether your vehicle will benefit after the work is complete.

References: EDF — Home charger installation and supply phases

7kW vs 22kW charging time: compare the same top-up

Use one consistent energy requirement for all options. In this worked example, a hypothetical 60kWh usable battery goes from 20% to 80%, adding 36kWh. At an assumed 90% efficiency, 40kWh is needed from the grid. Dividing 40kWh by each input power gives the simple constant-power times below. No named vehicle or measured session is being represented.

The 22kW line is only relevant if the car, chargepoint and property all allow 22kW AC. If the car is limited to 11kW, the 11kW result remains the relevant one even when comparing a more powerful wallbox. Real sessions can take longer when charging pauses or the vehicle reduces its draw.

Daily mileage can change the decision

Now consider a smaller daily requirement: 30 miles at an illustrative vehicle efficiency of 3 miles per kWh. That represents 10kWh of battery energy. At 90% charging efficiency, the grid requirement is about 11.1kWh. At a constant 7kW input it takes about 1 hour 35 minutes; at 11kW, about 1 hour 1 minute.

Both may fit easily into a long parking window. If the household’s real difficulty is a short turnaround between journeys, extra usable power may matter much more. Keep the daily-driving example separate from the occasional large top-up. Choosing around only the most extreme possible session can lead you to pay for capacity that your routine rarely needs.

Check whether the cheap-rate window is the constraint

Power matters differently when you want most charging to fit within a limited off-peak period. Suppose, purely as an example, you have four hours at the lower rate. A 7kW input can supply 28kWh from the grid in that time under constant-power assumptions, or 25.2kWh to the battery at 90% efficiency. An 11kW input could deliver 39.6kWh to the battery on the same assumptions.

This calculation gives a capacity boundary, not a prediction of what your particular tariff or car will do. Check our guide to off-peak EV charging tariffs and verify your supplier’s current schedule and any smart-charging conditions. A vehicle arriving with more charge may need much less energy than this example; a property power restriction may reduce what fits in the window.

Compare total cost with the benefit you can use

Request separate prices for the charger and any extra work needed to use its higher rating. Then write down the benefit in ordinary terms: a shorter wait, more energy within a tariff window or flexibility for another planned vehicle. Avoid translating saved charging time directly into cash unless it changes an actual cost or constraint for you.

For a hypothetical upgrade costing £900 more and reducing electricity spending by £90 a year, the simple payback would be ten years before considering maintenance, finance or changing tariffs. As shown in our detailed guide on home EV charging costs, running the numbers with your real unit rates prevents paying for hardware whose capacity you rarely utilise.

A short decision checklist

Before ordering, confirm the car’s AC rating, the assessed property limit, the charging window and a normal battery top-up. Run those numbers first using our charging time estimator. Then rerun a demanding journey scenario and compare the result with a lower-powered option. Ask what happens when other household loads are active, rather than assuming nameplate power is continuously available.

Use the calculator to expose the limiting factor, not to override an installer’s design. If vehicle or property capacity is the bottleneck, spending more on the wallbox alone may not shorten the session. Keep the written specification and assumptions with the quotation so you can compare alternatives on the same basis.