208 volt and 240 volt Booster Water Heaters up to 18kW, and 480 volt in 4kW and 5kW Compact Electric Booster Water Heaters, can be ordered in single phase. While 240 volt in 24kW through 45kW and 208 volt in 24kW through 39kW Booster Water Heaters may be ordered in single phase, consultation with the factory and written confirmation is required, due to high amperage in these types of applications.