To calculate the amount of power to match our daily consumption needs, we need to make a detailed list of all the electric appliances we switch on regularly. For example, using the washing machine three times a week is not the same as using it once a fortnight. Equally, having night storage heating is not the same as having natural gas heating which, logically, uses far less electricity.

Consumption habits
A house of four people using a fridge, washing machine, dishwasher, oven, glass-ceramic hob, TV, basic lighting and, now and again, basic electric appliances (hairdryers, heaters and a toaster, for example), the correct amount of power needed will be around 4,400 watts: some 22 euros a month according to the Iberdrola power calculator. This calculation takes for granted that the most power-hungry appliances are not all needed at once.

We should take into account the fact that if we apply for an electric power supply of 1,100 watts, our bills will be very different than if we apply for 5,500 watts of power. Each amount of power requires a fixed monthly payment, to which the tariff (usually 2.0 for private homes) and the variable costs of our consumption must be added.

Variation in the amount of power applied for
It is possible that you have purchased a second-hand property whose electric supply is lower or higher than you currently need. To apply for the amount of power corresponding to your needs, you need to ask the electric company to make the change. To do this, you need to follow a series of steps.

Firstly, you need to write to your electric company. Then, according to the existing legislation, an authorised electrician should visit your home and issue a bolet�n de instalaciones (installation report), that confirms that the home's interior or local installation is correct and fulfils all safety requirements. This step must be carried out and paid for by the consumer before changing the amount of power supplied.

The installation report should also specify the maximum amount of power that the property can handle. The supplier will never allow us to exceed this limit without completely changing the home's electricity installation. Electric companies suggest consulting them on whether a night storage rate is applicable if you have air conditioning, night storage heaters or electric heating.

If you want to reduce the current energy supply, the new amount will come into effect from the following bill, with a maximum delay of 60 days. In the event of an increase, this will come into effect from the date the contract is modified.

Did you know�?
- Frying an egg on a glass-ceramic hob costs 0.006 euros.
- A complete washing machine cycle costs 0.054 euros.
- One hour of TV costs 0.01 euros.
- Heating up a glass of milk in the microwave costs 0.002 euros.

Average cost of appliance:
- Conventional heater: 1,200 watts.
- Oil-based heater: 1,600 watts.
- Microwave oven: 800 watts.
- Fan: 300 watts.
- Hoover: 650 watts.
- Mixer: 500 watts.
- Coffee machine: 750 watts.
- Combi fridge: 600 watts.
- Washing machine: 800 watts.
- Iron: 750 watts.
- TV: 120 watts.
- Hair dryer: 1,000 watts.
- Air conditioning: 1,850 watts.

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