Good question, and not always easy to answer. In theory, 3Ks (the norm in most apartments) should be sufficient to handle the needs of a “standard” household, with husband, wife and a child as a baseline. It’s the most common and least expensive output. With a fridge, washer, washing machine and one AC unit, you should be fine.
But should is the key word — as it often is in Italy. Depending on the wiring and the age of the appliances, 3Ks could also blow out, particularly if you run the appliances at once (hair dryers and space heaters can be lethal). In a larger apartment with several AC units, washer, dishwasher, electrical equipment (oven, heater, etc.), 3Ks is like Scotty to Kirk: “Captain, she cann’a take any more ‘a this…”
If 3K is giving you trouble, you have the option of moving up to 4.5K or 6K, which the latter giving you free range to have everything on at once.
But both 4.5K and especially 6K come with a steep surcharge, anywhere between 40 and 100 percent higher than 3K (billing is bimestrale, or once every two months). If you like keeping your AC units on high and regularly use your washer, dishwasher you could face a few thousand euros when the bill drifts in.
Get an electrician in to have a look at your fuse box (both in the apartment and the condo one, if it has one). Tell him what appliances you expect to be running and how frequently. His answer won’t be foolproof but at the very least he can tell you if 3K is asking for trouble. Italian families generally run appliances less often than North American ones, who run a lot at once without a problem. Most don’t have driers. Energy prices are lower.
Little appliances can wreak havoc. In addition to hair dryers and space heaters (stuffe), that means toasters, and microwaves. Power converters can also cause surges that bring your apartment to a standstill.
ENEL has a comprehensive site that includes an English option. You do need to register first. The area clienti or customer service pages provide pricing information. You can also call them at 800.130.330. The same holds true for the other two giants, ENI and ACEA. Smaller providers include Edison. Their toll free number is 800.141.414
If you’re living on a farm, more is power required. Again, it all starts with a visit from a qualified electrician who knows his stuff, as well as the area, and can identify your power sources and their age… the older the appliances, the more they drain.