What are condensers, economizers and condensing hot water boilers?

The economizer, condenser and economizer on coal-fired boilers are actually the same, but they are called differently. Installed at the rear of the boiler. The flue gas temperature of boiler is very high. After installing these equipment, the water of the equipment can be heated by using the flue gas temperature to increase the temperature of the boiler feed water. So as to reduce the exhaust temperature of the boiler and achieve the purpose of saving fuel.