There are four main types of vacuum hot water boiler equipment, The first type is a horizontal internal combustion gas-fired vacuum hot water boiler for hot water supply, The second type is a horizontal internal combustion fuel oil type vacuum hot water boiler for supplying air-conditioning hot water, The third type of horizontal internal combustion fuel vapor dual-purpose vacuum hot water boiler for supplying air-conditioning hot water. The fourth type is a horizontal electric heating type vacuum hot water boiler for supplying hot water.