Electric boilers are very efficient for heating large homes because they do not have the heat loss associated with fossil fuel burning boilers. The annual fuel utilization efficiency of an electric boiler is in the 90th percentile for most modern units.
The boiler requires no exhaust vent, so it doesn't release heat as gases. The price of electricity can make gas-fired boilers a more economical choice. Boilers can deliver water throughout a home to multiple delivery devices without the heat loss from ducted systems. Outdoor units are less efficient than indoor units. Boilers can also be used to heat the hot water needed for radiant flooring.