The short answer
Time-of-use tariffs charge different unit rates at different times of day. Whether one suits you depends on when your air conditioning and the rest of your home use electricity, and how those rates compare with what you pay now.
On this page
Some air conditioning use can move to a different time and some can't: a bedroom can be cooled before bed, but a hot afternoon in a sunny living room happens when it happens. A tariff change also applies to everything else in your home, so the sums need to cover both.
How they work
A time-of-use tariff needs a meter that records when you use electricity, not just how much. That's usually a smart meter, which records use in half-hour periods. Older two-rate tariffs use a meter with separate day and night readings.
| Type | How the price varies |
|---|---|
| Two-rate, such as Economy 7 | A cheaper rate for a set block of hours overnight |
| Peak and off-peak | Cheaper overnight, pricier in a late afternoon and early evening peak |
| Dynamic | A different price for each half hour, published in advance |
| Cheap-window tariffs | Set cheap periods, sometimes only for homes with an electric car, battery or heat pump |
Rates, hours and conditions differ between suppliers, so read the details rather than relying on a tariff's name. If a tariff is limited to certain equipment, check whether your system qualifies. Northern Ireland has a separate energy market, so the tariffs on offer there are different.
When air conditioning uses electricity
- Cooling is needed most in the afternoon and evening, which can overlap with a late-afternoon peak. Cooling a bedroom through the night can fall largely in the cheaper hours of a tariff with an overnight rate.
- Heating is needed most in the early morning and the evening, and the evening part can overlap with a peak too.
- Pre-cooling or pre-heating means running the unit before a peak so it can do less during it. A cooler room gains heat faster and a warmer one loses it faster, so this uses some extra energy. It only helps when the price gap is wide enough, and works best with blinds, curtains and doors closed.
Timers and schedules and smart controls and apps make it easier to run the unit at the right times without having to remember.
Working out whether it helps
- Find out when your household uses electricity. With a smart meter, your supplier may be able to show your half-hourly use.
- Estimate how much the air conditioner uses, and when. How much does air conditioning cost to run? explains the method.
- Price all of your use on each tariff you're considering, including the standing charges.
The example below uses made-up rates: a single-rate tariff at an example 25p per kWh, and a time-of-use tariff at an example 12p overnight, 22p in the day and 35p in an evening peak. It compares two ways a unit might use the same 4 kWh in a day. Pattern A is like a bedroom cooled overnight, with a little use in the day and evening; pattern B is like a living room that needs cooling in the evening sun.
| Period | Example rate | Pattern A | Pattern B |
|---|---|---|---|
| Overnight | 12p | 2 kWh | 0 kWh |
| Daytime | 22p | 1 kWh | 1 kWh |
| Evening peak | 35p | 1 kWh | 3 kWh |
| Cost | 81p | £1.27 |
On the single-rate tariff, both patterns cost £1.00. On the time-of-use tariff the same energy comes to 81p in one pattern and £1.27 in the other, which is why the timing of your use decides the result. Real tariffs differ in their rates and their hours, so check your own tariff and repeat the sum with its figures.
Before you switch
- Standing charges can differ between tariffs, so include them in the comparison.
- The rest of your home moves to the new rates too, including cooking, laundry, electric showers and any electric car charging.
- Contract terms, including any exit fees, affect how easily you can change your mind.
- Dynamic prices can be high when demand is high, so they suit people who check them or can automate their use.
- Comfort comes first in a heatwave. In very hot weather, follow the NHS's advice on keeping cool rather than waiting for a cheaper hour.
Related guides
- How much does air conditioning cost to run?Multiply the electricity it uses, in kWh, by your unit rate. How much a unit uses depends on the room, the weather, the temperature you set and its efficiency, so estimate it from its average power draw and the hours it runs.
- Timers and schedulesMost systems have on and off timers that count down a set number of hours, and many controllers and apps add clock times and weekly schedules. Used well, they have a room comfortable when you need it and the system off when you don't.
- Air conditioning and solar panelsSolar panels can supply some or all of an air conditioner's electricity while they're generating, which suits cooling on sunny days far better than heating in winter. Solar electricity you use yourself costs you any export payment you'd otherwise have earned.
- How to cut running costsSet a moderate temperature, stop heat getting in (or out, in winter), run the unit only where and when you need it, and keep the filters and outdoor unit clean. Your tariff matters too.