What is the energy voltage in United States houses?

I think you mean "what is the voltage of the electric power distribution in US houses" It's called 240 volt single phase, which is a misnomer, as it is actually two phases of 120 volts each. Most outlets are connected to one of those phases and supply 120 volts to appliances. Some appliances that require more power connect to both phases for 240 volts.

Addendum to the answer:

The answer above might look a bit vague, the voltage in the US is 120V (same as Canada, most of Europe is 220-240 V), the electrical frequency is 60 Hz. Plugs used are A or B.