Which type of heating system does not use ducts for distribution?

Boilers represent a type of heating system that operates without the use of ductwork for distributing heat. Instead of heating air, boilers heat water, which then circulates through pipes to radiators or underfloor heating systems in a building. This hydronic heating process allows for effective distribution of warmth throughout spaces without relying on ducts, making boilers a unique option within heating systems.

In contrast, furnaces operate by using fuel to generate heat, which is then distributed via ducts throughout the home. Heat pumps can also use ductwork, typically in the form of forced air systems, to move heated or cooled air. Electric heaters usually work by converting electricity into heat and can operate in standalone units or as part of a system with ductwork, depending on the design. Therefore, the distinguishing characteristic of a boiler is its reliance on water circulation rather than air distribution through ducts.