The short answer is both. The whole-home electrical water heaters will require a 220-Volt plug that is not always available where you need it. They need this plug because there is so much power needed to heat the water that a standard 110-Volt heater will not be able to keep up. The 110-Volt units will fit a standard home wall outlet, which makes installation seamless in most cases. They draw less power, so they do not require the additional voltage that the whole-home system requires.