Yes, a boiler is necessary for radiant heat. Radiant heat is a type of heating system that uses hot water or steam to warm the floor or walls of a room. The boiler is responsible for heating the water or steam, which is then circulated through pipes in the floor or walls. Boilers come in a variety of sizes and types, so it is important to choose the right one for your needs. For example, a gas-fired boiler is more efficient than an oil-fired boiler, but it may require more maintenance. Additionally, the size of the boiler should be based on the size of the space you are heating.