Houses using the Economy 7 tariff require a special electricity meter which provides two different readings - one for the day period and one for the night period. The night (off-peak) period lasts for seven hours, hence the name.
The wiring in the house does not need to be altered. The night storage heaters and hot water boilers are on the ordinary circuit, but only switch on when the night rate is activated. Any electrical appliance in use during this period therefore runs at a lower rate of billing, such as fridges, freezers, dish washers or a washing machine set to start using a timing device.
The specific times when Economy 7 applies vary between different regions and at different times of year. Usually the seven-hour period starts at 1:30am during summer and 12:30am in winter. Some regions use radio teleswitching to control consumers' systems and vary the timing — this uses data carried on the 198 kHz BBC Radio 4 LW signal.
As an example of price tariffs during 2006, Ecotricity charged 22.03 UK pence per kilowatt hour (kWh) for the first 728 kWh's of day usage (per annum) and 12.13 UK pence per subsequent kWh and 4.63 UK pence per off-peak kWh. Whilst Npower charged 17.25 UK pence per kilowatt hour for the first 705 kWh's of day usage, 10.89 UK pence per subsequent unit use and 3.95 UK pence per off-peak kWh. Consequently a house requires at least 20% of its consumption during the off-peak period to save money.